Principles of Inheritance PDF

Genetics AND Evolution ----------------------The work of Mendel and others who followed him gave us an idea of_____________ _____________________________. However the nature of those ____________________which determine the ______________________was not very clear. As these ‘_________________’ repre...

Genetics AND Evolution ----------------------The work of Mendel and others who followed him gave us an idea of_____________ _____________________________. However the nature of those ____________________which determine the ______________________was not very clear. As these ‘_________________’ represent the_______________ _______________________________, understanding the structure of _____________________________and the structural basis of ___________________and ______ _________________conversion became the focus of attention in biology for the next century. The entire body of molecular biology was a consequent development with major contributions from -------------------- 1. Watson, 2. Crick, 3. Nirenberg, 4. Khorana, 5. Kornbergs (father and son), 6. Benzer, 7. Monod, 8. Brenner, etc. A parallel problem being tackled was____________________________________. Awareness in the areas of 1. molecular genetics, 2. structural biology and 3. bio informatics have enriched our understanding of the molecular basis of evolution. In this unit the structure and function of DNA and the story and theory of evolution have been examined and explained. _________________________________was born in Chicago on 6 April 1928. In 1947, he received B.Sc. degree in Zoology. During these years his interest in bird- watching had matured into a serious desire to learn genetics. This became possible when he received a Fellowship for graduate study in__________________________________ ___________________________, Bloomington, where he received his Ph.D. degree in 1950 on a study of the___________________________________________________ ______________________________. He met Crick and discovered their common interest in____________________________________________. Their first serious effort, was unsatisfactory. Their second effort based upon more experimental evidence and better appreciation of the nucleic acid literature, resulted, early in March 1953, in the proposal of the_______________________________________________________________ ______________________________. _____________________________________________________was born on 8 June 1916, at Northampton, England. He studied physics at University College, London and obtained a B.Sc. in 1937. He completed Ph.D. in 1954 on a thesis entitled “X-ray Diffraction: Polypeptides and Proteins”. A critical influence in Crick’s career was his friendship with J. D. Watson, then a young man of 23, leading in 1953 to the proposal of the____________________________________________________________ _______________________________________. Crick was made an F.R.S. in 1959. The honours to Watson with Crick include: the John Collins Warren Prize of the Massachusetts General Hospital, in 1959; the Lasker Award, in 1960; the Research Corporation Prize, in 1962 and above all, the Nobel Prize in 1962. CHAPTER 4 PRINCIPLES OF INHERITANCE AND VARIATION Have you ever wondered why an elephant always gives birth only to a baby elephant and not some other animal? Or why a mango seed forms only a mango plant and not any other plant? Given that they do, are the offspring identical to their parents? Or do they show differences in some of their characteristics? Have you ever wondered why siblings sometimes look so similar to each other? Or sometimes even so different? These and several related questions are dealt with, scientifically, in a branch of biology known as Genetics. This subject deals with_____________________________, as well as the variation of characters from___________________________________. Inheritance is the process by which characters are passed on____________________ __________________________; it is the______________________________. Variation is the degree by________________________________________________. Humans knew from as early as ____________________________that one of the causes of variation was_____________________________________________________________. They _______________________________________that were _____________________ in the _________________________________________________________________to _____________________________and _____________________________that possessed desirable characters. For example, through ___________________________and ______________________ from ancestral wild cows, we have well-known Indian breeds, e.g.,_____ ____________________________________. We must, however, recognise that though our ________________________________ about the___________________________________________________________, they had very little idea about_______________________________________________________. MENDEL’S LAWS OF INHERITANCE It was during the mid-nineteenth century that headway(means progress ) was Commented [MO1]: made in the__________________________________________________. Gregor Mendel, conducted _________________________________________ ____________________for seven years (___________________________) and proposed_______________________________________________________________. During Mendel’s investigations into inheritance patterns it was for the first time that ________________________________and ___________________________________ were applied to_________________________________________. His experiments had a_______________________________________, which gave greater credibility(means capacity for belief) to the_______________________________________. Also, the confirmation of __________________________________________________on successive_______________________________________________________, proved that his results _____________________________________________________________rather than being unsubstantiated ideas. Mendel investigated characters in the garden pea plant that were______________ ________________________, e.g., __________________________,_____________ ________________________. This allowed him to set up a basic framework of___________________________ _______________________, which was _______________________________________ to account for ______________________________________________________ and the __________________________________in them. Mendel conducted such _____________________________/_________________________ experiments using several true-breeding pea lines. A truebreeding line is one that, having__________________________________________, shows ------------- the ________________________________________________________and ____________________________________________________________. Mendel selected______________________________________________________ ______________________, as pairs which were similar except for _________________ _______________________________________________________________ Some of the contrasting traits selected were ---------------- _________________________________________, ____________________________________________, _____________________________________(full) or ____________________________________________________________and ______________________________________________ (Figure 4.1, Table 4.1). 2 INHERITANCE OF ONE GENE Let us take the example of one such hybridisation experiment carried out by Mendel where he ____________________________________________________to study the inheritance of one gene (Figure 4.2). He ______________________________produced as a result of _______________ and ______________________to generate plants of the____________________ ______________________.  This generation is also called___________________________________________. Mendel observed that all ___________________________________were tall, like______________________________; ________________________(Figure 4.3). He made similar observations for the_____________________________________– he found that the ___________________________________________either one of the parents, and that the _____________________________________was not seen in them. Mendel then _______________________________________________________and to his surprise found that__________________________________________ ___________________________; the character that was not seen in the F1 generation was now________________________________. The proportion of plants that were dwarf were ____________________________________________________-while _______________________________________________were tall. _________________________________________________________________to their parental type and did not show any blending, that is all the _________ _________________either_______________________________, none were of in _____________________________ (Figure 4.3). Similar results were obtained with the other traits that he studied: only one of the parental traits was expressed _________________________________________ while at the _____________________________________________were expressed in the ______________________________________ The contrasting traits did not show any blending at either _____ ____________________________ Based on these observations, Mendel proposed that something was being _____________________________________, ______________________________________, from ________________________________through the__________________, over________________________________________________. He called these things as ‘factors’.  Now we call them as genes. _____________________, therefore, are the_________________________________. _________________________________-that is required to express a particular____ _________________________________________. Genes which code for a pair of____________________________________ _____________________________, i.e., they are slightly__________________ ___________________________. If we use alphabetical symbols for each gene, then the capital letter is used for the _____________________________ ______________________________and the small alphabet for___________________________________. For example, in case of the character of height, T is used for ________________________________________and t for ________________________________and T and t are___________________________________. Hence, in plants _________________________for height would be _________ ____________________ Mendel also proposed that in a_________________________, tall or dwarf pea variety the allelic pair of genes for height are __________________________or____ ___________________________, ____________and_______________, respectively. _____________________________called the _____________________ of the plant while the descriptive terms _______________________________are the____________________________. What then would be the phenotype of a plant that had a genotype Tt? As Mendel found the ______________________of the _______________________ Tt to be exactly like the TT_____________________________________________, he proposed that in -------------- a pair of__________________________________________, one ______________________________________(as in the F1 ) and hence is called the ____________________________while the other factor is ______________________________________.  In this case T (for tallness) is dominant over t (for dwarfness), that is__________ __________________________. He observed _________________________________for all the other ___________________________/______________________ that he studied. It is convenient (and logical) to use the _____________________________ ___________________________________to remember this concept of _____ ___________________________and_______________________________________. (Do not use T for tall and d for dwarf because you will find it difficult to remember whether T and d are alleles of the same gene/character or not). ____________________________________________as in the case of _________ ________________________________or can _____________________________ _____________________the case of the____________________________________. Since __________________________________________for genes controlling one character (height), it is a monohybrid and the cross between _______and _____is a_______________________________________________. From the observation that the ___________________________________________ is expressed without any blending in the___________________________________, we can infer that,--------------- when the________________________________________________, by____________________________________________________, the _____________________________________________________or segregate _____________________________________________and only _________________________________________________to a gamete. This ________________________________________is a random process and so there is a _________________________________________containing either allele, as has been verified by the______________________________________________. In this way the _____________________________________________________have the allele T and the _______________________________________________plants have_____________________________________.  During fertilisation the_________________________________, ______________________________________________say, ___________________________________________________, and _______________________________________________________, __________________________________________, are united to ___________________________________________that have one _______________________and one____________________________. The__________________________________________. Since these hybrids contain alleles which express_____________________________, the___________________________________________. The production of gametes by the parents, _______________________________ , ______________________________________________can be understood from a diagram called _______________________________as shown in Figure 4.4 1. It was developed by a____________________________, ____________________________________________. 2. It is a graphical representation to calculate the probability of all possible_______________________ _____________________________________________. 3. The ____________________________ are written on____________________________, usually the___________________________________________. 4. All possible combinations are represented in__ _____________________________________________, which generates a square output form. 5. The Punnett Square shows the _________ ____________________________________(male) and _________________________________(female) plants, the ______________________________________and, the F1 Tt progeny. 6. The F1 plants of____________________ ___________________________________________. The symbols are used to denote the __________________(_________) and ___________(________________) of the___________ ________________________, respectively. The F1 plant of the_______________________________ , ___________________________ of the genotype ________and __________in equal proportion. When fertilisation takes place, the ____________________________of _____________ have a _____________________________chance to___ ______________________________________________, as well as of_____________________________________. Also _______________________________________ ______________________________have a 50 per cent chance of_____________________________________ , as well as____________________________________. As a result of random fertilisation, the resultant ___________________________________________ ______________TT, Tt or tt. From the Punnett square it is easily seen that------------------ ___________________random __________________lead to_____________, ____________lead to ________and _________to__________. Though the F1 have a genotype of Tt, but the __________________ _____________________________________‘_______________’. At F2 , 3/4th of the plants are tall, where some of _______________ __________________while___________________________________. Externally it is not possible to distinguish between the_______________ _____________________________________________________. Hence, within the genopytic pair________________________________ __________________________________. Hence the character T or ‘tall’ is said to dominate over ____________ _____________or ‘_______________’ character. It is thus due to this dominance of one character over the other that all the ___________________________(though the genotype is Tt) and in the ____________________________________________________ (though genotypically 1/2 are Tt and only 1/4th are TT). This leads to a__________________________________________________: (____________________________) and______________________________, i.e., a 3:1 ratio, but a__________________________________________. The 1/4 : 1/2 : 1/4 ratio of TT: Tt: tt is------------- mathematically condensable to the form of the ___________________ (__________+_________)_______, that has the gametes bearing genes ____________________________________________________. The expression is expanded as given below : (___________________________) 2 = (_________________________) X (___________________________) = ________________+ _________ + ________________________  Mendel self-pollinated ____________________and found that ________ _________________continued to generate ____________________ _________________________.He concluded that the _______________ ______________________________________________________________ What do you think he would have got had he self- pollinated a tall F2 plant? From the preceeding paragraphs it is clear that though the ____________ ________________________________can be calculated using____________ ___________________________________, by simply looking at _the_________________________________________________________, it is not possible to know the genotypic composition. That is, for example, whether a ____________________________ _______________________has _______or ________composition, cannot be predicted. Therefore, to determine the genotype of a tall plant at F2 , Mendel crossed the__________________________________________ _____________________. This he called a__________________________. In a typical ______________________________________(pea plants here) showing a ________________________________(and whose genotype is to be determined) is crossed with the _________ ___________________instead of____________________. The progenies of such a cross can easily be analysed to predict the________ ______________________________________________________________.  Figure 4.5 shows the results of _________________________________ where violet colour flower (W) is dominant over white colour flower (w). Using Punnett square, try to find out the nature of offspring of a test cross. What ratio did you get? Using the genotypes of this cross, can you give a general definition fora test cross? Based on his observations on monohybrid crosses Mendel proposed two general rules to consolidate his understanding of___________________________ ___________________________________________. Today these rules are called the Principles or Laws of Inheritance: ------------------- 1. the First Law or _______________________________________and 2. the Second Law or____________________________________________. 4.2.1 Law of Dominance (i) Characters are controlled by___________________________________________. (ii)___________________________________________. (iii) In a dissimilar pair of factors ___________________________________________ (___________________) the other (____________________________). The law of dominance is used to explain the expression of only one of the _________________________________________________________________in the F1 and___________________________________________________________. It also explains the____________________________________________________________ _____________. Law of Segregation This law is based on the fact that the ____________________________________ and that both the __________________________________________________ though one of these is not seen at the F1 stage. Though the parents contain_____ ____________________________________________, the __________________or ______________________________________from each other such that a gamete__________________________________________________________. Of course, a _______________________________________produces all gametes that _____________________________while a ________________________one produces ___________________________________________________each having ________ _____________________________________________ Incomplete Dominance When experiments on peas were repeated using other traits in other plants, it was found that sometimes the _________________________________________that did not ________________________________________________________________and was in between the two. The _________________________________________________________ (_____________________________________________________________)is a good example to understand incomplete dominance. In a cross between _______________________________________________(RR) and _________________________________________________________________(rr), the F1 (Rr) was pink (Figure 4.6). When the _______________________________ __________________________________________________________________ (RR) Red: 2 (Rr) Pink: 1 (rr) White.  Here the ______________________were exactly as we would expect in any___ _________________________________, but the phenotype ratios had changed from the_________________________ :________________________________. What happened was that R was not completely dominant over r and this made it possible to distinguish Rr as pink from RR (red) and rr (white). Explanation of the concept of dominance: What exactly is dominance? Why are some alleles dominant and some recessive? To tackle these questions, we must understand what a gene does. Every gene, as you know by now, contains the _________________ ______________________________ _________________________ In a diploid organism, there are two copies of each gene, i.e.,_______ _______________________________. Now, __________________________________need not always be_______________, as in a____________________________. One of them may be different due to some changes that it has undergone (about which you will read further on, and in the next chapter) which modifies the____ ____________________________________________________________________. Let’s take an example of a gene that contains the information for producing an enzyme. Now there are two copies of this gene,____________________________________. Let us assume (as is more common) that ---------------------- the normal allele produces the normal enzyme that is needed for the transformation of a substrate S. Theoretically, the modified allele could be responsible for production of – (i) the __________________/_____________________________________, or (ii) a__________________________________________________________, or (iii) ________________________________________________In the first case, the ___________________is equivalent to the_____________________, i.e., it will produce the _________________________/_____________, i.e., result in the_____________________________________________________. Such equivalent allele pairs are very common. But, if the allele produces a __________________________________________or____________________ , the_____________________________________________. The phenotype/trait will only be dependent on the_______________________ __________________________________________________. The unmodified (functioning) allele, which represents the original phenotype is the ___________________________________and the modified allele is generally the________________________________. Hence, in the example above the ________________________________________due to ______________ _________________________or because ___________________ ________________________is produced. Co-dominance Till now we were discussing ___________________________________________either of the __________________________(dominance) or was ____________________ (incomplete dominance). But, in the case of ____________________________________________________ ______resembles both parents. A good example is different types of ____________________________________ ______________________________________in human beings. ABO blood groups are controlled____________________________________. The plasma membrane of the red blood cells has ___________________________ that ______________________________________and the kind of______________ ______________________________________________________________________. The gene (I) has three alleles I A , I B and i. The alleles I A and I B produce ________________________________ while______________________________________________________________. Because________________________________________________________, each person possesses any________________________________________________. I A and I B ________________________________________________________i, in other words when ____________________________________________________ (because i does not produce any sugar), and when _________ _____________________________________________________I B expresses. But when I A and I B are present together they both_____________________ ____________________________________: this is because of__________________. Hence red blood cells have both A and B types of sugars. Since there are three different alleles, there are ________________________ ____________________-of these________________________________________, and therefore, a total of _____________________________________________ _____________________________________(Table 4.2). How many phenotypes are possible? Do you realise that the example of ______________________________also provides a good example of__________________________? Here you can see that there are more than ___________________________ ___________________________________________________ Since in an individual only_____________________________________ ______________________________, ______________________________ only when population studies are made. Occasionally, a _______________________________________________may produce____________________________________________. For example, _________________________in pea seeds is_____________________ _____________________. It has ___________________________(B and b). _____________________________effectively by ____________________ ________________________and therefore, __________________ ________________________are produced. In contrast, ____________________________have lesser efficiency in _______________________________and produce__________________ _______________________________.  After maturation of the seeds, B B seeds _______________________and the b b seeds_________________________. Heterozygotes produce_____________________________, and so B seems to be the________________________________. But, _____________________ produced are of___________________________________________________. So if _______________________________is considered as_________________ , then from this angle, the alleles show_________________________________. Therefore, ____________________________________________________________of a gene or the product that it has information for. It depends as much on the ____ __________________________________________________________from this product as it does on the particular phenotype that we choose to examine, in case more than__________________________________________________________ ___________________________. INHERITANCE OF TWO GENES Mendel also worked with and _____________________________that differed in___ _________________________, as is seen in the cross between a pea plant that has seeds--------------- with ________________________________and ______________________________and _________________________________________________and _________________________ (Figure 4.7). Mendel found that the seeds resulting from the crossing of the parents, had____ ________________________________________. Here can you tell which of the characters in the pairs yellow/ green colour and round/wrinkled shape was dominant? Thus, ____________________________________over __________________ _______________dominant__________________________________. These results were identical to those that he got when he made separate _______________________________between _________________________ plants and between _________________________________________________plants. Let us use the genotypic symbols -------------- Y for _____________________________________and y for____________________________________________________, R for ____________________________________________________and r for__________________________________________________. The genotype of the parents can then be written____________________________. The cross between the two plants can be written down as in Figure 4.7 showing the genotypes of the parent plants. The ____________________________________________________on fertilisation to produce________________________________________. When __________________________________________________________he found that ----------------------- ____________________________________________had yellow seeds and _________________________________________________. The______________________________________________________________. ____________________________________________________ ______________________________________; just like in a monohybrid cross. Law of Independent Assortment In the dihybrid cross (Figure 4.7), the phenotypes round, yellow; wrinkled, yellow; round, green and wrinkled, green appeared___________ __________________. Such a ratio was observed for _________________ __________________________that Mendel studied. The ratio of ______________________________________as a combination series of_________________:,___________________:______________________. This derivation can be written as follows: (_____________________________) (___________________________) = 9 Round, Yellow :__________________, Yellow:_________________, Green :____________,  ______________________upon such observations on ______________________ _(crosses between plants differing in two traits) Mendel proposed a ________________________________________________that we call_____________________________________________________________ ______________________________________. The law states that ‘when two pairs of traits are_____________________________ , segregation of one pair of ____________________________________________of the_________________________________________________________’. The Punnett square can be _________________________________________ the independent segregation of the two pairs of genes during ________________ and _______________________________and pollen in_____________________. Consider the segregation of__________________________________________. ____________________________________________have the gene R and the other ________________________r. Now besides each gamete having either________________, it should also have the____________________________. The ______________________________________________________here is that _____________________of 50 per cent R and 50 per cent r is _____ __________________from the __________________________of 50 per cent Y and 50 per cent y. Therefore, 50 per cent of the ______________________________________and the other_____________________________________________________. Similarly, 50 per cent of the _______________________________________and the other________________________________________. Thus there are ____________________________________________________ (four types of pollen and four types of eggs). The four types are_____, ______, ________and _________each with a frequency of __________ or ____________ the total gametes produced. When you write down the four types of eggs and pollen on the two sides of a Punnett square it is very easy to ____________________________________ that give ________________________________________________(Figure 4.7). Although there are 16 squares how many different types of genotypes and phenotypes are formed? Note them down in the format given. Can you, using the Punnett square data work out the genotypic ratio at the F2 stage and fill in the format given? Is the genotypic ratio also 9:3:3:1? 4.3.2 Chromosomal Theory of Inheritance Mendel published his work on inheritance of characters in 1865 but for several reasons, it remained______________________________. Firstly, ______________________was not easy (as it is now) in those days and his work could not be__________________________. Secondly, his ___________________________(or factors, in Mendel’s words) as stable and discrete units that controlled _________________________________ and, of ______________________________________________________‘blend’ with each other, was not _______________________________________________ as an explanation for the apparently___________________________________ _____________________________________. Thirdly, Mendel’s approach of using ___________________________________ ______________________________was totally new and unacceptable to many of the biologists of his time. Finally, though Mendel’s work suggested that ____________(genes)________ ________________________________, he could not provide any physical proof for the ______________________________________or say what they were made of. In 1900, three Scientists 1. ___________________________, 2. _________________________and 3. ___________________________. independently rediscovered Mendel’s results on the inheritance of characters. Also, by this time due to ____________________________________________ that were taking place, scientists were able to carefully____________________. This led to the discovery of structures in the nucleus that appeared to _______ and____________________________________________________________. These were called _____________________________(_____________________ , as they were visualised by staining). By 1902, the ______________________________________________had been worked out. _________________________________and _______________________ noted that the behaviour of ______________________________was parallel to the ______________________________________________and used ________________________________________________(Figure 4.8) to explain Mendel’s laws (Table 4.3). Recall that you have studied the behaviour of chromosomes during mitosis (equational division) and during meiosis (reduction division). The important things to remember are that _________________________as well as _______________________occur in pairs. The _______________________________________________are located on ________________________________on____________________________ _____________________ During Anaphase of meiosis I, the ____________________________________can align at the ___________ ____________________________independently of each other (Figure 4.9). To understand this, compare the chromosomes of _____________________ ____________________________________________________________. In the left column (Possibility I) _____________________________________ _______________________together. But in the right hand column (Possibility II) the ___________________________________________________________with the___________________________________________. ____________________________________argued that the pairing and separation of a ___________________________________would lead to the ________________________________________________________they carried. Sutton united the knowledge of _____________________________________ ______________________________and called it the _____________________ __________________________________________. Following this synthesis of ideas, experimental verification of the ____________ ____________________________________________________________and his colleagues, led to discovering the basis for the variation that _____________ _______________________________. Morgan worked with the _________________________________________ ______________________(Figure 4.10), which were found very suitable for such studies. They could be grown on _________________________________________in the laboratory. They complete their life cycle in______________________________, and a ____________________________________________________a large number of progeny flies. Also, there was a clear differentiation of the sexes – the male and female flies are easily distinguishable. Also, it has many types of _________________________ ___________________that can be seen with_________________________. 3 Linkage and Recombination Morgan carried out _______________________________________________in Drosophila to study genes that were___________________________. The ___________________________________________________________ carried out by Mendel in peas. For example ----------------------- Morgan hybridised_____________________________, ______________________ to_____________________________, _________________________________ and intercrossed their F1 progeny. He observed that the ____________________________________________ ______________________of each other and the ___________________________ very significantly from the ________________________________(expected when the______________________________________________________________). Morgan and his group knew that ________________________________________ (Section 4.4) and saw quickly that when the ________________________________ were situated on the____________________________________, the proportion of __________________________________________________were much higher than the______________________________________. Morgan attributed this due to ---------------------- the __________________________________or ___________________________________________________________and ____________________________________________to describe this physical association of _________________________________________and the term recombination to describe the _________________________ ____________________________________________________(Figure 4.11). Morgan and his group also found that even when __________________ ________________________on the__________________________________, some genes were very ______________________________(showed very low recombination) (Figure 4.11, Cross A) while __________________________ (showed higher recombination) (Figure 4.11, Cross B). For example he found that the _____________________________________ __________________________and showed only __________________ _________________________while ________________________________ showed__________________________________________________________. His student Alfred Sturtevant used the frequency of-------------- recombination between ___________________________________________ as a measure of the ___________________________________________and ‘_______________________’ their position on the___________________. Today genetic map sare extensively used as a ________________________ __________________________of whole genomes as was done in the case of the Human Genome Sequencing Project, described later. POLYGENIC INHERITANCE Mendel’s studies mainly described those traits that have distinct alternate forms such as___________________________________________________________. But if you look around you will find that there are many traits which are not so distinct in their _________________________and are___________________ _____________________. For example, in humans we don’t just have tall or short people as two distinct alternatives but a_____________________________________________________. Such traits are generally controlled by three or more genes and are thus called as polygenic traits. Besides the involvement of __________________________________________ ________________________________also takes into account the influence of environment. Human ____________________________is another classic example for this. In a polygenic trait the phenotype reflects the_____________________ ________________________, i.e., the__________________________________ _________________________. To understand this better let us assume that __________________________ ___________________________________in human with the ________ _________________________________responsible for dark skin colour and the ____________________________________________for light skin colour. The genotype with all the dominant alleles (AABBCC) will have ____________________________ _______________________________and that with all the ________________________________________(aabbcc) will have the_________________________________________. As expected the genotype with ------------------------ __________________________________________and _________________ __________________________________will have an intermediate skin colour. In this manner the number of each type of alleles in the genotype would determine ________________________or ___________________________ in an individual. PLEIOTROPY We have so far seen the effect of a gene on a___________________________. There are however instances where a________________________________ ________________________________________________________________. Such a gene is called_____________________________________. The underlying mechanism of pleiotropy in most cases is the effect of a __________________ __________________________which contribute towards__________________ _____________________________-. An example of this is the disease______________________________________, which occurs in humans. The disease is caused by ____________________________________________that codes for the ________________________________________________________ (single gene mutation). This manifests itself through phenotypic expression characterised by ________ _____________________and a ____________________________________and__ _________________________________-. SEX DETERMINATION The ____________________________________________________________has always been a puzzle before the_________________________. The initial clue about the _________________/___________________________ __________________________ can be traced back to some of the experiments carried out in___________________. In fact, the ___________________________________________made in a ____ ___________________led to the development of the concept of____________ ________________________________________________________________. ________________(1891) could trace a specific nuclear structure all through __________________________________in a few insects, and it was also observed by him that _______________________________________________________this structure after spermatogenesis, whereas the_____________________________ __________________________________________--. Henking gave a name to this structure as the _________________________but he could not explain its significance. Further investigations by other scientists led to the conclusion that the ‘__________________’ of ______________________________________________ ___________________ and that is why it was given_____________________________________________. It was also observed that in a large number of insects the_________________ __________________________________________________________, i.e., all eggs bear an ____________________________________________besides the other chromosomes (autosomes). On the other hand, some of the ___________________________________ ____________________________whereas some do not. Eggs fertilised by ___________________________________________ become females and, those fertilised by sperms that do not have _________ __________________________________________ Do you think the number of chromosomes in the male and female are equal? Due to the ________________________________________________________in the determination of sex, it was_________________________________________ , and the rest of the chromosomes were named____________________. ___________________________is an example of XO type of sex determination in which the ____________________________________ besides the autosomes, whereas___________________________________ ___________________. These observations led to the ___________________________________ to understand the_____________________________________________. In a number of other insects and mammals including man, ____________ _________________________is seen where both male and female have same_________________________________________. Among ________________________________________________________is present but its counter part is distinctly _______________________and called the______________________________________. Females, however, have a_________________________________________. Both males and females bear same number of________________._ Hence, the males have_____________________________________, while female have______________________________________________________. In human beings and in Drosophila the males have _______ chromosome, whereas females have a _____________________________besides _________________________(Figure 4.12 a, b). In the above description you have studied about two types of sex determining mechanisms, i.e., _________type and _________type. But in both cases males produce two different types of gametes, (a) either _______________________________________________________or (b) some gametes with __________________and some with________________. Such types of sex determination mechanism is designated to be the example of_____________________________________. In some other organisms, e.g., birds, a different mechanism of sex determination is observed (Figure 4.12 c). In this case the total number of ___________________________________in both males and females. But ______________________________________________in terms of the sex chromosomes, are_______________________________________, i.e., female heterogamety. In order to have a _______________________________________ ___________________________described earlier, the two different sex chromosomes of a female bird has been _____________________ _________________________________________________________________ In these organisms the females have ________________________________and__ ___________________________, whereas males have a pair of _______________________________________besides the autosomes. Sex Determination in Humans It has already been mentioned that the ________________________________ in case of____________________________________________________. Out of 23 pairs of chromosomes present,_____________________________ ____________________________________________________________; these are the autosomes. A ___________________________________________________in the female, whereas the presence of an _______________________________________are determinant of the_______________________________________________. _____________________________________among males,_________________ __________________________________. _________________________ _______________________________produced carry the X-chromosome and the rest _____________________________________________besides the autosomes. Females, however, produce only one type of________________________ ___________________. There is an _____________________________________ of the ovum with the sperm _________________________________________ or____________________________________. In case the _________________________________________________ the zygote develops into ____________________(XX) and the _________ _________________________________________________________carrying sperm results into a male offspring. Thus, it is evident that it is the genetic makeup of the________________ _____________________________________________. It is also evident that in each pregnancy there is always __________________ of either a______________________________________________. It is unfortunate that in __________________________________________ ______________________________ and have been ostracised and ill- treated because of this false notion. Sex Determination in Honey Bee The sex determination in honey bee is based on the number of____________ __________________________________. An offspring formed from the _________________________________and an __________________________________________________(queen or worker), and an _____________________________________________(drone) by_____________________________________________________________. This means that the ______________________________________________ than________________________. The females are ____________________having ________________________ and males are__________________, i.e., having_________________________. This is called as ____________________________________________________ and has special characteristic features such as the ____________________ ______________________________________(Figure 4.13), they do not ______ ________________and thus cannot_________________, but have a ________ ___________________and can have grandsons. How is the sex-determination mechanism different in the birds? Is the sperm or the egg responsible for the sex of the chicks? MUTATION Mutation is a phenomenon which results in _________________________ ____________________and consequently results in ____________________ _____________________and_______________________________________. In addition to________________________________, mutation is another phenomenon that leads to_________________________________________. As you will learn in Chapter 5, one _____________________________ continuously from one end to the other in___________________ , in a________________________________________. Therefore _______________(_____________________) or __________(______________/_ ___________________) of a segment of DNA, result in_____________________ ______________________________. Since genes are known to be_________________________________________ , alteration in chromosomes results in___________________________________ ____________________________. _______________________________________________are commonly observed__________________. In addition to the above, __________________ _________________due to change in a_________________________________ __________________. This is known____________________________________. A classical example of such a mutation is___________________ _________________________. Deletions and insertions of base pairs of DNAcauses_____________ _______________________________________________(see Chapter 5). The mechanism of mutation is beyond the scope of this discussion, at this level. However, there are many chemical and physical factors that_________________ _______________________. These are referred to as_______________________. _________________________________________________________mutations in organisms – it is a mutagen. GENETIC DISORDERS 1. Pedigree Analysis The idea that _________________________________________has been prevailing in the human society since long. This was based on the ____________________ ____________________________________________________in families. After the rediscovery of Mendel’s work the practice of analysing ________________________________________________in human beings began. Since it is evident that _________________________________________ ___________________________________or some other organisms, are not possible in case of human beings, study of the _______________________ __________________________________of a particular trait provides an alternative. Such an __________________________________in a several of generations of a family is called the_______________________________________________. In the pedigree analysis the _____________________________________ is represented in the__________________________________________________. In human genetics, ____________________________________________ _________________________________, which is utilised to trace the inheritance of a_________________________, ______________________or_____________. Some of the important standard symbols used in the pedigree analysis have been shown in Figure 4.13 As you have studied in this chapter, each and every feature in any _____________ ________________________________________________________ by one or the other gene ___________ ________________________________present in the chromosome. DNA is___________________________________________________________ It is hence transmitted from one generation to the other without any ____ ______________or________________________. However, changes or alteration do_______________________________. Such an alteration or change in the ______________________is referred to_________________________. A number of disorders in human beings have been found to be associated with the _____________________________________________or ___________________ or__________________________________. 2. Mendelian Disorders Broadly, genetic disorders may be grouped into two categories – ____________________________disorders and _______________________________disorders. Mendelian disorders are mainly determined by _____________________ ______________________________________________________ These disorders are transmitted to the ___________________________ as we have studied in the principle of inheritance. The pattern of inheritance of such ____________________________________ in a family by_____________________________________________. Most common and prevalent Mendelian disorders are --------------------- ______________________________, ________________________________, _________________________________, _________________________________, __________________________________, _________________________________, etc. It is important to mention here that such Mendelian disorders may be _____________________________________________________________ __________________________________________________________whether the trait in question is dominant or recessive. Similarly, the trait may also be ___________________________________ as in case of__________________________________. It is evident that this X-linked recessive trait shows transmission from_________ ________________________________________________________. A representative pedigree is shown in Figure 4.14 for dominant and recessive traits. Discuss with your teacher and design pedigrees for characters linked to both autosomes and sex chromosome. 3. Colour Blidness : It is a ___________________________________________________________due to defect in either ______________________________________________resulting in _______________________________________________between red and green colour. This defect is due to mutation in certain genes___________________________ ____________________________. It occurs in about _____________________ and only about_____________________________________________________. This is because the genes that lead to___________________________________ ___________________________. Males have only ______________________ and______________________________________. The son of a woman who carries the ______________________________ ________________________colour blind. The mother is not herself colour blind because__________________________. That means that its effect is__________________________________________ _______________________________________. A daughter will not normally be colour blind, unless her ____________________________________________and her father is___________________________________. Haemophilia : This ____________________________________________disease, which shows its transmission from __________________________________________________to _______________________________________________has been widely studied. In this disease, a single protein that is a part of the ______________ __________________________________________________________is affected. Due to this, in an affected individual a simple cut will result______________ __________________. The ______________________________________(carrier) for haemophilia may transmit the disease to sons. The possibility of a ___________________________________________________is extremely rare because mother of such a _______________________________ _________________________________and the father should be _______________ (______________________________________________________________). The _____________________of Queen Victoria shows a number of _____________________________________________________________as she was a___________________________________________. Sickle-cell anaemia : This is an ___________________________________________________that can be transmitted from _________________________________________________when both the partners are ________________________________________________ (or heterozygous). The disease is controlled by a single pair of ____________________________, ________________________and _____________________. Out of the ___________________________________________________ individuals for ________________________________________________show the diseased phenotype. ____________________________(HbAHbS ) individuals appear apparently ______________________but they are ________________________________ as there is ________________________________________________________of the____________________________________________________, thus exhibiting sickle-cell trait (Figure 4.15). The defect is caused by ___________________________________________(Glu) by _____________________(Val) at the _____________________________ ______________________of the haemoglobin molecule. The substitution of _______________________________________________ results due to the single base substitution at the ________________________ __________________gene from________________________________________. The mutant haemoglobin molecule undergoes _______________________ ___________________________causing the change in the shape of the RBC from _________________________________________________________(Figure 4.15). Phenylketonuria : _____________________________________________________is also inherited as the________________________________________. The affected individual lacks an enzyme that converts the______________________________ _______________________________________. As a result of this _________________________________________________and converted into______________________________________________________. Accumulation of these in brain results in_________________________________. These are also excreted through urine because of its_________________________ _______________________________. Thalassemia : This is also an _____________________________________________________ transmitted from parents to the offspring when both the partners __________ _____________________________________________________(or heterozygous). The defect could be due to either ___________________________________which ultimately results in reduced rate of synthesis of __________________________ (________________________________) that make________________________. This causes the ________________________________________________ resulting into anaemia___________________________________________. _______________________________can be classified according to which chain of the_____________________________________________________________. In________________________, production of _______________________ __________________________________while in_____________________ ______________________, production of______________________________. α Thalassemia is controlled by two closely linked genes ______________________________________________________of each parent and it is observed due to mutation or deletion of___________________________ _______________________. The more genes affected, the ___________________________________produced. While β Thalassemia is controlled by a single gene __________ _______________________________and occurs due to mutation of one or both the genes. Thalassemia differs from _______________________________________in that the former is a quantitative problem of ___________________________ _______________________while the latter is a qualitative problem of synthesising an________________________________________________________________. Chromosomal Disorders The chromosomal disorders on the other hand are caused due to ______________________or _______________________or abnormal arrangement of_______________________________________. ________________________________________________________during cell division cycle results in the _______________________________________(s), called____________________________. For example, ____________________________results in the gain of extra copy of chromosome 21. Similarly, _______________________________results due to loss of an X chromosome in human females. ________________________________after telophase stage of cell division results in an increase in a _________________________________________________and, this phenomenon is known as___________________________. This condition is often seen____________________________________. The total number of chromosomes in a normal __________________________ (_________________). Out of these ___________________________________ and one pair of____________________________________________________. Sometimes, though rarely, either an additional copy of a chromosome may be included in __________________________________________________may lack one of any one pair of chromosomes.  These situations are known as_______________________________ , respectively. Such a situation leads to very serious consequences in the individual. ______________________________________, ______________________________________, _________________________________________. are common examples of chromosomal disorders. Down’s Syndrome : The cause of this genetic disorder is the presence of an additional copy of the _____________________________________________________(______________ _____________). This disorder was first described by___________________________(__________). The affected individual is ---------------------- ______________________________________________, __________________________________and ___________________________________ (Figure 4.16). Palm is______________________________________________________. __________________, ______________________and ______________ _______________________is retarded. Klinefelter’s Syndrome : This genetic disorder is also caused due to the presence of an additional copy of __________________________________________________________, XXY. Such an individual has overall _________________________________--, however, _______________________________ (development of_______________, i.e.,______________________________) is also expressed (Figure 4.17 a). Such individuals are________________________. Turner’s Syndrome : Such a disorder is caused due to the___________________________________, i.e., ______________________, Such ______________________________as ___________________________________________________________ other _______________________________________ (Figure 4.17 b)