Chapter 20: Inheritance (PDF)

Ôj úoHdj Biology Inheritance 20.1 Diversity among organisms 20 You know that there are large numbers of plant or animal species in the bio...

Ôj úoHdj Biology Inheritance 20.1 Diversity among organisms 20 You know that there are large numbers of plant or animal species in the biosphere. One species can be identified separately from another species by observing their external features. We get this ability as these species possess inherited features. Inherited characters are the features that transmit from generation to generation. Although there are common characteristics for a species all the organisms belong to a single species are not similar. The body features of every human is not similar. There are many differences among them. (Fig - 20.1) Figure 20.1 - Diversity of human living in different areas in the world You can identify differences within species like cats and parrots. Figure 20.2 - Diversity of cats and parrots 169 For free distribution y 5RVHDQG2UFKLGSODQWVWKDWJURZLQ\RXUKRPHJDUGHQDOVRSURGXFHÀRZHUV with different colours and sizes. (Fig-20.3) Figure 20.3 - Roses and Orchids of different colours & sizes You can observe Tomato and Brinjal plants that grow in your home garden with fruits of different shapes. (Fig-20.4) Figure 20.4 - Different varieties of Tomatoes and Brinjals We will consider few common inherited characteristics of human species. 170 For free distribution ² Common inherited characteristics in human population We will identify different common inherited characteristics observed in human in the pictures below. Figure 20.5 - Skin colour (Complexion) -white, fair, dark Figure 20.6 - Curly and straight hair Figure 20.7 - Fused or free earlobes Figure 20.8 - Ability to fold the tongue Figure 20.9 - Position of the thumb Figure 20.10 - Dimpled and normal cheeks ZKHQWKH¿QJHUVDUHFURVVHG 171 For free distribution  Figure 20.11- Straight and curved thumb Figure 20.12 - Widow's peack on forehead Activity 20.1 y Prepare a table using above inherited characteristics of your mother’s and father’s relatives. y Using above information identify characteristics and skills that have transmitted from generation to generation. y Study whether you or your brother, sister or any other relative has got a new characteristic which was not found in any relative of the generation. According to the observation of the above activity it is revealed that most of the mother’s and father’s characteristics have passed to the next generations. But you may have found new characteristics in your brother, sister or any other relative which is not found in any relative. If you further study previous generations you PD\¿QGWKDWSDUWLFXODUFKDUDFWHULVWLFLQWKHP,WLVFOHDUWKDWLQKHULWHGFKDUDFWHULVWLFV may pass evading from one generation to the next. There are some rare inherited characteristics. Identify them using the pictures bellow. 172 For free distribution  Figure 20.13 - - Syndactyly Figure 20.14 - -Polydactyly Figure 20.16 - -Brown or blue eyes Figure 20.15 - -Albinism Transmission of inherited characteristics is common to all organisms. Other than human other plants and animals possess inherited characteristics. Do the assignment 20.1 to determine those characteristics. Assignment 20.1 y Select few plants or animals found in your home garden. y Record few characteristics of them which have not changed for the past time period. It is clear that according to the collected information the nature of complexion, ears, teeth, foot, wings, skin pattern, beak are inherited characteristics. Taste of fruits, FRORXURIÀRZHUVQDWXUHRISRGVDQGVHHGVDQGKHLJKWRIWKHSODQWDUHDOVRLQKHULWHG characteristics. dggee For extra knowled Figure 20.17 - Growth of muscles due to exercises 173 For free distribution  7KH¿UVWSHUVRQWRVWXG\DERXWWKHWUDQVPLVVLRQ of inherited characteristics is an Austrian priest, and a science graduate Gregor Mendel. He is honoured as the father of genetics. Figure 20.18 - Gregor Mendel 20.2 Mendel’s experiments about inheritance He used the garden pea (Pisum sativum) plant for his experiments in 1865. He has used that partcular plant for his experiment because of its special features. The reasons to select the garden pea plant for his experiment are as follows. y Can be easily grown y Can obtain the yield within a short time period y Can obtain pure breeding plants. (The selected characteristics are not changed for many generations) y Naturally self pollinating. When necessary cross pollination is also possible y Ability to obtain off springs by breeding and can continue the generations y He observed 7 contrasting characters and tested one character at a time The procedure he followed for the tall and short character was as follows, Œ Cultivation of pure breeding tall and short plants. These parental generation was known as P Œ Pollens of tall plants were deposited on stigma of short plants, and vice versa Œ Obtain new seeds by cross-pollination and plant them to obtain the next generation. All plants were tall and they are referred to as F1 generation Œ Allow self-pollination to take place within F1 generation Œ The resultant seeds were planted to obtain the F2 generation. The tall to short plant ratio was 3 : 1. 174 For free distribution Œ It was a question to Mendel, that what has happened to short character in F1 generation. According to Mendel’s opinion, the tall character was dominant and short was recessive. Assignment 20.2 Mendel has used large number of samples and repeatedly done the experiments WRFRQ¿UPKLVFRQFOXVLRQV$QDO\VHKRZ0HQGHOKDVFDUULHGRXWKLVH[SHULPHQW DFFRUGLQJWRVFLHQWL¿FPHWKRG The feature which was recessive in F1 generation reappear in F2 generation. It was an important observation. As Mendel used a single pair of contrasting characters at a time, it was known as Monohybrid cross. y The inherited pattern of a Monohybrid cross The results obtained from the Mendel monohybrid cross using 7 different contrasting characters are given in the below table. Table 20.1- The results of the experements of Mendel Character Cross F1 F2 generation Closest generation Dominant Recessive ratio Colour of the Purple x white Purple Purple 705 White 224 3:1 ÀRZHU Colour of the Yellow x Green Yellow Yellow 6022 Green 2001 3:1 seed Shape of the Round x Wrinkled Round Round 5474 Wrinkled 3:1 seed 1850 Shape of the ,QÀDWHG[ ,QÀDWHG ,QÀDWHG Constricted 3:1 Pod Constricted 299 Colour of the Green x Yellow Green Green 428 Yellow 152 3:1 Pod Position of Axial x terminal Axial Axial 652 Terminal 207 3:1 ÀRZHU Height of the Tall x Short Tall Tall 787 Short 277 3:1 plant 175 For free distribution It is clear that all above characters, are inherited in the same manner. One feature is completely hidden in F1 generation and it reappears in F2 generation. This is the recessive feature. In both generations all the plants were with the features of P generation. No pea plants were with intermediate characters. Mendel assumed that it was because two different factors determine a single characteristic. In genetics, symbols are used to denote those factors. The standard is that the dominant factor is denoted by a capital letter and the recessive by a simple letter. Accordingly, » For tall feature T, » For Short feature t is used For each inherited feature 2 factors are involved. y Pure breeding Tall plants TT y Pure breeding short plants tt. y The tall plants with recessive short feature Tt. When two factors are similar, they are known as homozygous, (TT, tt) when the factors are not similar they are known as heterozygous (Tt).The monohybrid cross of pea plant, considering tall and short character can be expressed using symbols as below. (Fig - 20.19 (a)) Punnett square (Fig - 20.19 (b) )which was introduced by a scientist called Punnett can be used to show the occurrence of F2 generation. P Generation TT tt P Generation TT x tt Gametes Gametes T t F1 Generation F1 Generation Tt x Tt Tt Gametes Gametes T t T t F2 Generation TT Tt F2 Generation TT Tt Tt tt (a) Tt tt (b) Figure 20.19 - Monohybrid cross of Pisum sativum 176 For free distribution  Assignment 20.3 y Select another pair of contrasting feature of pea plant using 20.1 table. y State pure breeding dominant character or pure breeding recessive character using symbols. y Build up a punnett square to show the inheritance of this monohybrid character. y Explanation of patterns of inheritance using probability When any two different objects combine randomly, the result will take place according to a particular pattern. As an example consider random combination of X & Y objects. (x + y) (x + y) Two characters present in parents inherit into off springs randomly. Carryout below activity to identify the probability xx + xy + xy + yy (Probability means the ability of an incident to happen.) Do you know ? The probability of getting the head or the tail when tossing a coin is 1/2 The bead experiment is similar to relationships of probabilities using WZRFRLQVDWDWLPH7R¿QGRXW+HDG±+HDG+HDG±7DLO7DLO±+HDG 7DLO±7DLOSUREDELOLWLHVWKHSUREDELOLWLHVREWDLQHGIURPHDFKFRLQKDVWR be multiplied. Then the probability is 1/2 × 1/2 = 1/4 :KHQWKHVDPHLQFLGHQWWDNHVSODFHLQWZRZD\V (JJHWWLQJ+HDG±7DLO DQG7DLO±+HDG LVWKHWRWDORIVHSDUDWHO\WDNHQSUREDELOLWLHV That is 1/4 + 1/4 = 1/2 177 For free distribution  Activity 20.2 ,GHQWL¿FDWLRQRISUREDELOLW\SDWWHUQVREWDLQHGE\DEHDGH[SHULPHQW y Divide the class into 4 to 5 groups. y Provide 2 vessels with mixture of 50 white beads (W) & 50 red beads (R) to each group (instead of beads, can use buttons or seeds with two different colour can be used) y Take out a bead from two vessels at a time & note the colour of two beads with tally marks in the relevant column and return them into the same vessels. y Likewise continue it for 50 times & tabulate results. y Present the results to the class. RR RW WR WW 1 st Group 2 st Group ''' ''' ''' ''' Total ''' ''' ''' ''' Fill the above table using results obtained by the above practical using tally marks Calculate, I. Times of Red - Red beads & probability of getting Red - Red. ii. 7LPHVRI5HG±:KLWH 3UREDELOLW\RIJHWWLQJ5HG±:KLWH iii. 7LPHVRI:KLWH±5HG 3UREDELOLW\RIJHWWLQJ:KLWH±5HG iv. 7LPHVRI:KLWH±:KLWHDQGSUREDELOLW\RIJHWWLQJ:KLWH±:KLWHEHDGV 8VLQJWKRVHSUREDELOLW\YDOXHV¿QGRXWWKHUDWLRRI555::5:: Let’s analyse the Mendel’s results using the probability results obtained by the bead experiment. 178 For free distribution From 1st & 2nd vessels. L 7KHSUREDELOLW\RIJHWWLQJ5HG±5HG  ii) The probability of getting White - White = 1/4 LLL  7KHSUREDELOLW\RIJHWWLQJ5HG±:KLWH  LY  7KHSUREDELOLW\RIJHWWLQJ:KLWH±5HG  rd th In (iii) & (iv) instances, both show the same incidence, both vessels, L 7KHSUREDELOLW\RIJHWWLQJ5HG±5HG  LL  7KHSUREDELOLW\RIJHWWLQJ:KLWH±:KLWH  LLL  7KHSUREDELOLW\RIJHWWLQJ5HG±:KLWH   The ratio between probability is = 1/4 : 2/4 : 1/4 1 : 2 : 1 According to Mendel’s monohybrid cross, the ratio of F2 genotypes, TT, Tt, tt is 1:2:1 Similarly the probability ratio of bead experiment compatible with the genotypes of F2 generation. 20.3 Basic concepts of genetics y Gene concepts about inheritance Mendel said that the features of an organism is determined by a special particular IDFWRUV7KHLGHQWL¿HGSDUWLFXODUIDFWRULVQDPHGDVJHQHVODWHU In gene concept, as a standard the dominant feature is denoted by a capital letter and the recessive by a simple letter. We have already used these letters in Mendel monohybrid cross. If two genes are similar for a given feature of an organism, it is said that this organism is homozygous for that feature, or else that organism possess homozygous genes. If two genes are not similar then that organism is heterozygous, or else that organism possesses heterozygous genes. Example :- Gene for round seed is R, Gene for wrinkled seed is r y Homozygous situations, RR or rr y Heterozygous situations Rr 179 For free distribution y Gene expression The combination of a gene pair for a particular character is known as gene expression of that organism. Example :- Rr, rr, Rr y Phenotype & Genotype The feature that externally appears is known as phenotype. The gene composition to determine that feature is known as genotype. Examples :- y The phenotype of round seed heterozygote is round. The genotype is Rr y The phenotype of round seed homozygote is round. The genotype is RR y The phenotype of wrinkled seed homozygote is wrinkled. The genotype is rr ‡ Nature of genetic material & genes 6FLHQWLVWV KDYH LGHQWL¿HG WKDW WKH 'HR[\ ULER 1XFOHLF $FLG '1$  SUHVHQW LQ chromosomes acts as the genetic material that transmits features of organisms from generation to generation. 7KHGRXEOHKHOLFDOVWUXFWXUHRI'1$ZDV¿UVWGLVFRYHUHGE\WZRVFLHQWLVWVQDPHG Watson & Crick in 1953. According to the sequence of base pairs in DNA strand, different genetic information are stored. The features of organisms are determined by the sequence of base pairs. Accordingly DJHQHLVDVSHFL¿FEDVHVHTXHQFHLQD'1$PROHFXOHUHVSRQVLEOHIRUDSDUWLFXODU FKDUDFWHU,QRWKHUZD\JHQHLVDVSHFL¿FVHJPHQWRI'1$IRUDSDUWLFXODUFKDUDFWHU The genes that determine large number of features in an organism and transmit them from generation to the next are present in chromosomes. Each gene has a particular location in a chromosome. 180 For free distribution  For extra kowledge A DNA DNA mo mole le lecu cule le iiss a cl cloc ockw kwisisee tw twin twined ined ed ddou oublble ble he heli lica call st stru ruct ctur cturee of ttwo wo sstr tran trands ds ttha that hatt ru runn an anti ti parall para llel el ttoo ea each ch ooth therer.. Th Thee tw twoo st stra rand ndss ar aree jo join ined ed bbyy Ad Adeneninine, e, T Thyhymi mine ne C Cytytos osin inee & Gu Guananin inee nitr ni trog ogen enououss ba base se ppai airs rs.. Th Thes esee co comb mbininat atio ions ns iinn DN DNA A ar aree de denonote tedd as A – T T,, C – G (F(Fig ig - 220. 0.20 20)) A fo forr Ad Aden enin ine, e, T ffor or T Thyhymi mine ne,, C foforr Cy Cyto tosi sine ne & G ffor or GGuauani nine ne.. Two strands with sugar and phosphate grups Phosphate group Sugar groups Base pairs Figure 20.20 - Double helical model of a DNA molecule ‡ Gene linkage A pair of chromosomes that are arranged to the same sequence of characters are known as homologous chromosomes. They are same in length, width and the location of centromere. An organism receives this homologous chromosomes from its parents, one from mother and the other from father. A pair of genes that determine a particular character are present in complementary locations of homologous chromosomes. It is clear in Mendel’s experiment that during gamete formation, these genes, independently segregate. A scientist called Morgon also did experiments about genetics. He got unexpected phenotypic ratios, and found out that, the genes do not segregate always independently. The genes that present in the same chromosome which are not segregated independently are known as linked genes. Morgon discovered the gene linkage. 181 For free distribution 20.4 Heredity of human Transmission of inherited characters to next generation is known as heredity. The process by which those characters transmit is known as inheritance. You have already learnt that the characters of organisms pass to the next generations by the genes of chromosomes. The behaviour of genes & chromosomes during inheritance has mentioned above in gene linkage & meiosis. The behaviour of chromosomes during sex determination of human is discussed under inheritance. Even though the chromosomes in a nucleus of a cell are different in shape & size, the number of them is constant for a species. It is a unique feature of a species. Below are the number of chromosomes present in nuclei of different organisms. Table - 20.2 Number of Paddy 24 Organism chromosomes Tomato 24 E. Coli Horse 1 33 Bacteria Mouse 40 Garden 14 Pea Human 46 Onion 16 Chimpanzee 48 Maize 20 Carp 104 20.5 Sex determination of human You may prefer to know how your gender is determined. This incidence is known as sex determination. We will look at how the sex is determined. There are 46 chromosomes, or 23 pairs of chromosomes, in a human cell. Out of those 23 pairs, 22 pairs are autosomal chromosomes and the remaining pair is the sex chromosomes. 182 For free distribution  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 X Y Figure 20.21 - 22 pairs of Autosomal chromosomes Figure 20.21 - 22 pairs of Autosomal chromosomes and sex chromosome pair of a female and sex chromosome pair of a male Two sex chromosomes of a female are similar in structure & shape. They are known as X chromosomes. The sex chromosomes of a male are different from each other. They are known as X & Y chromosomes. The Y chromosome is smaller than X. The X chromosome of males is similar to the X chromosome of females. During formation of an egg from an egg mother cell and sperms from sperm mother cell the pair of sex chromosomes separate. A sperm contains 22 autosomal chromosomes & only a single sex chromosome. An egg possesses only a X chromosome & a sperm contains a X or a Y chromosome. When an egg gets fertilized with a sperm, there may be two X chromosomes or X & a Y chromosomes in the zygote. A zygote with two X chromosomes produces a girl & X & Y chromosomes produces a boy, Accordingly the factor that needs to determine a boy is received from the father and not the mother. The sex determination is shown in the diagram 20.23. The probability of getting a girl or a boy is 50%. 183 For free distribution  Egg mother Sperm mother cell cell x x x y Eggs Sperms x x x y xx xx xy xy Female Female Male Male 50] 50] Figure 20.23 -Sex determination of human Assignment 20.3 How the females to males ratio will affect the composition of population in a country ? Discuss with your teacher using data of past census. 20.6 Human inherited disorders y Genetic disorders due to sex linked inheritance Even though X & Y chromosomes determine the human sex, all the genes present on those sex chromosomes, are not used in determination of sex. Most of the genes on X & Y chromosomes, determine other features as autosomal chromosomes. As Y chromosomes is shorter than X chromosome, most of the genes complementary for X are absent in Y. Accordingly, in males for most of the X linked genes, there are no complementary genes in Y. 184 For free distribution Therefore most of the genes in X, whether they are dominant or recessive, they are phenotypically expressed in males. But as females possess a pair of X chromosomes, X linked genes are paired. They phenotypically express a recessive character only when they are present as double recessive genes. We will consider several genetic disorders, occur due to sex linked recessive genes. y Haemophilia Carrier Haemophilia which occurs due to a X Healthy uj mother mshd linked recessive gene only present in father males in the population. When a wound or cut occurs, it is essential to clot blood. At that time when a blood clot is formed, it stops excessive bleeding. Haemophilic patients, blood does not clot. Therefore they die because of bleeding. Females act as carriers for this disease. Healthy Healthy Carrier Diseased frda.S daughter son daughter son - ecessive gene for Haemophilia h-R H - - Dominant gene of the recessive gene for Haemophilia Figure 20.24 - Inheritance of Haemophilia y Colour blindness (Red – Green colour blindness) This is the most common sex linked inherited disease. The reason for this disease is, a recessive gene in X chromosome. The sufferer cannot distinguish red colour from green colour. This is common among males rarely occur in females. When a colour blind female is married to a healthy male the inheritance of colour blindness is given in the below diagram. The chance to show the sex linked inherited diseases in females is low, the chance of getting those diseases in female children is high if they are married to blood relatives. The reason for that is the female that joined the family is most probably a carrier. 185 For free distribution  Diseased Healthy mother uj mshd father c - Recessive gene for colour blindness C - Dominant gene of the recessive gene for colour blindness Carrier Diseased Carrier Diseased daughter son daughter son Figure 20.25 - Inheritence of colour blindness y Gene mutations & related inherited disorders Due to a change in DNA of a chromosome, the mutations occur in a single gene, are known as gene mutation. When a naturally active gene is mutated, it gets inherited, we will look at few genetic disorders that occur due to a mutated gene. Do you know ? Occurence of gene mutations takes place due to several reasons. They are y Spontaneous without any external effects y Due to radiations y Due to chemicals y Albinism Natural complexion is due to a pigment called Melanin. This disorder occurred due to a mutation of the gene is responsible for the production of the above pigment present in an autosomal chromosome. The features of this disorder are the abnormal white colour of skin, hair and eye lashes. Albinism occurs when gene is present as recessive homozygous condition. Not only human but also animals become albino. (Fig - 20.26) 186 For free distribution  Figure 20.26 - Albone child & Albone peacock y Thalassemia This is a condition that occurs due to a mutation in a gene responsible for the production of haemoglobin. Haemoglobin is a protein that acts as a carrier for O2 transportation in blood. Due to reduction of haemoglobin production in thalassemic patients, the main symptom is anaemia. Homozygous recessive tt, condition is diseased. Heterozygous Tt condition is the carrier. There are several areas in Sri Lanka with higher number of thalassemic patients. The reason for that may be the marriages between blood relatives. For extra knowledge ‡ Application of knowledge of inheritance Since long time man has understood that by selecting animals and plants with better qualities, can produce quality hybrid plants and animal varieties. Cows that can produce higher volume of milk, hens that produce large number of eggs, chicken ZLWK KLJKHU JURZWK UDWH FURSV ZLWK KLJK \LHOG RU SHVW UHVLVWDQW ÀHVK\ VHHGOHVV 187 For free distribution fruits (Fig-20.27) are examples of genetic applications to improve quality of animal or plant products. Figure 20.27 - Improved seedless oranges :KHQ SULQFLSOHV RI JHQHWLFV ZHUH LGHQWL¿HG SURGXFWLRQ RI K\EULG SODQWV DQG DQLPDOVEHFRPHVDWHFKQRORJ\,WZDV¿UVWDSSOLHGDPRQJVRPHZKHDWFXOWLYDWRUVLQ America. The economy was developed as they have used improved wheat varieties. Now in Sri Lanka, crop research centres and breeding centres have achieved a considerable development in gene technology. Large sized fruits or vegetables, improved grains and livestock have been used WR IXO¿OOLQJ WKH QHHGV RI WKH JUHDWO\ LQFUHDVLQJ SRSXODWLRQ ,I ZH KDYH QRW XVHG JHQHWLFDOO\PRGL¿HGKLJKTXDOLW\SURGXFWVZHZRXOGQRWEHDEOHWRIXO¿OOWKHKLJK demand of food. Figure 20.28 - Improved vegetables & fruits 20.7 Genetic engineering New technology is being used to produce a recombinant DNA molecule, which is IRUPHGE\FRPELQLQJ'1$IUDJPHQWVRIGLIIHUHQWVRXUFHV7KLV¿HOGLVNQRZQDV 188 For free distribution Recombinant DNA technology. 7KLV¿HOGLVKLJKO\SRSXODUL]HGDVJHQHWLFHQJLQHHULQJRUJHQHWHFKQRORJ\ The genotype of an organism can be altered by removing or adding extra DNA fragments into genome. We will look at the application of gene technology in food and agriculture, medical DQGLQGXVWULDO¿HOGV y )RRGDQG$JULFXOWXUDO¿HOG 01. Production of high productive plants and animals Examples for plants and animals with better qualities that has produced using recombinant DNA technology. y Weedicide resistant crops - By inserting a gene obtained from a bacterium. y Pest resistant crops - By inserting a gene obtained from a soil bacterium. y Rice enriched with vitamin A (Golden rice) A gene that produces vitamin A in carrot is obtained and inserted into paddy. y $WRPDWRUHVLVWDQWWRFROGZHDWKHU%\LQVHUWLQJDJHQHREWDLQHGIURPD¿VK living in mud of cold countries. y +LJK SURGXFWLYH ÀHVK DQG PLON  FDWWOH DQG PLON ZLWK KLJK QXWULWLRXV YDOXH )RRGSURGXFHGE\JHQHWLFDOO\PRGL¿HGRUJDQLVP *HQHWLFDOO\PRGL¿HGIRRG   ,QGXVWULDO¿HOG Below are some instances where bacteria produced by gene technology are being XVHGLQLQGXVWULDO¿HOG y Production of enzymes such as Amylase. y Production of some amino acids. (To produce MSG - Monosodium Glutamate.) y Production of vitamins by (Cyanobacteria Eg :- vitamin B12 and E) 189 For free distribution y As a remedy to the pollution by fossil fuel combustion and other waste material'  0HGLFDO¿HOG *HQHWHFKQRORJ\LVXVHGLQGLIIHUHQWVHFWLRQVRIPHGLFDO¿HOG y Production of Insulin - Human gene related to Insulin production is inserted into E coli bacteria. y 3URGXFWLRQRISURWHLQVLQFOXGLQJJURZWKKRUPRQHV±%\LQVHUWLQJUHOHYDQW gene into a bacterium. y Use of developed bacteria and fungi in production of antibiotics. y Insertion of genes that is responsible for the formation of arteries in the embryo into patients with artery blockages (patients to carryout bypass surgery) to induce growth of new arteries. y Replacement of the diseased gene by a healthy gene. (gene therapy) y 8VH RI '1$ WHFKQRORJ\ WR FRQ¿UP WKH LGHQWLW\ RI D SHUVRQ LQ IRUHQVLF PHGLFLQH)RUWKHLGHQWL¿FDWLRQRIDFULPLQDOEORRGVDPSOHVHPHQKDLURU DNA of any other part of the body obtained from a site of crime are used. ,GHQWL¿FDWLRQRIWKHFULPLQDOE\FKHFNLQJWKHFRPSDWLELOLW\RIWKH'1$RI those samples mp with the suspects, pe s, DNA. Summary ‡ The diversity among organisms in the biosphere is because of the inherited features of each species. ‡ Inherited features are the characters that transmit from generation to generation. ‡ Within the same species too the organisms possess differences. ‡ There are common and rare inherited characters in human populations. ‡ 7KH ¿HOG WKDW VWXG\ DERXW WKH ZD\ WKDW WKH LQKHULWHG FKDUDFWHUV DUH transmitted is known as genetics. ‡ *UHJRU0HQGHOZDVWKH¿UVWSHUVRQWRFDUU\RXWH[SHULPHQWVUHJDUGLQJ inherited characters of plants. ‡ Mendel concluded that two factors, different to each other which are responsible for determining, a character of the pea plant. ‡ 7KHVHIDFWRUVWKDWGHWHUPLQHFKDUDFWHUVODWHULGHQWL¿HGDVJHQHV2QHRI these is a dominant gene and the other is a recessive gene. ‡ The pattern of inheritance of a monohybrid cross can be expressed in a chart. ‡ The pair of genes, responsible for a particular feature can be shown in a gene expression. 190 For free distribution  ‡ The externally expressed feature of an organism is phenotype. ‡ The gene composition that determines a particular phenotype is the genotype. ‡ The material that transmits features from generation to generation is the DNA in chromosomes. ‡ $VSHFL¿FQLWURJHQRXVEDVHVHTXHQFHRI'1$LVNQRZQDVDJHQH ‡ The number of chromosomes in nucleus is constant for a species. ‡ The pair of chromosomes that are similar in length, width and location of centromere is known as the homologous chromosome. ‡ The pair of genes responsible for a particular character present in complementary locations of the homologous chromosomes. ‡ The genes that are present in the same chromosome and that cannot be segregated independently are known as linked genes. ‡ The sex of human is determined by the way of association of sex chromosomes during fertilization. ‡ A zygote with two X chromosomes gives rise to a girl and a zygote with X and a Y chromosome gives rise to a boy. Exerices  5HG±JUHHQFRORXUEOLQGQHVVLVDQLQKHULWHGGLVHDVH6HOHFWWKHFRUUHFWJHQRW\SH of a carrier female. 1) XoXo 2) XcXo 3) XcY 4) XcXc 2. What is the percentage of parental genotypes received to the progeny if BB x bb cross is done ? 1) 100% 2) 75% 3) 50% 4) 0% 3. Parents with normal complexion, got a child with white skin. i) Is it possible to happen? ii) Explain your answer with the knowledge of genetics. 191 For free distribution 4. An improved organism by recombinant DNA technology has, i) Changed its genotype only ii) Changed its phenotype only iii) Changed its genotype and phenotype both iv) No effect on genotype and phenotype both 5. If you are given with a homozygous yellow seed plant where the green colour * LVGRPLQDQWDQG\HOORZFRORXU J LVUHFHVVLYH+RZGR\RX¿QGRXWWKH genotype of the green coloured seed plant? Explain your answer. 6. Sum of the genes in an organism is known as “genome”. Under human genome project, it has started to arrange the base sequence of genes (map) in chromosomes. Which is the statement that shows the harmful effect of the above to human? 1. Use of gene technology as a remedy for genetic disorders. 2. Ability to produce human with special features.  $ELOLW\RIWKHOLIHLQVXUDQFH¿UPVWRLGHQWLI\WKHDSSOLFDQWVKHDOWKFRQGLWLRQV easily. 4. As a remedy for food problem using improved plants and animals by gene technology. Technical terms Inhertance - m%fõ‚h- - y¨}{rÍ~ „• Heredity -- wdfõ‚h -- ]¨i\Wƒ Genetics -- m%fõ‚ úoHdj -- xŠƒx͊„5 Chromosome -- j¾Kfoayh -- xŠƒx͊˖£}xÊM Gene -- cdkh -- xŠƒx͊\ËWÊJ{ Gene expression -- cdk m%ldYkh -- y¨}{rÍ~ „“75r„ xÊX}{ Gene linkage -- cdk m%;snoaOh -- %‘=2]P„ƒ Sex determination -- ,sx. ks¾Kh -- ~Š{rÍ~ Genetical disorders -- cdkuh wdndO -- ~Š{–\ËWÊJ{ 192 For free distribution