IFY Week 1 Lecture-5 PDF

2/13/2024 BIOLOGY Ass. prof. Marium Shamaa Associate professor of Biochemistry and Molecular Biology, College of Pharmacy, AASTMT 1 DIFFERENCE BETWEEN GENOTYPE AND PHENOTYPE A person’s genotype is their unique sequence of DNA. More specifically, this term is used to refer to the two forms a person h...

2/13/2024 BIOLOGY Ass. prof. Marium Shamaa Associate professor of Biochemistry and Molecular Biology, College of Pharmacy, AASTMT 1 DIFFERENCE BETWEEN GENOTYPE AND PHENOTYPE A person’s genotype is their unique sequence of DNA. More specifically, this term is used to refer to the two forms a person has inherited from their mother and father, for a particular gene. Phenotype is the observable expression of this genotype – a person's presentation. A person’s phenotype results from the interaction between their genotype and their environment. 2 1 2/13/2024 DIFFERENCE BETWEEN GENOTYPE AND PHENOTYPE The terms Genotype and phenotype may sound similar, but there is a huge difference between genotype and phenotype. The genotype is a set of genes in DNA responsible for unique traits or characteristics, while the phenotype is the physical appearance or characteristic of an organism. Genotype The human genetic code could be found by their genotype. It determines the traits which will be expressed. Organisms that look the same do not have the same genotype. Biological tests can determine genotype Phenotype As discussed earlier, both the genotype and phenotype sound similar but have differences. The phenotype is determined by an individual’s genotype and expressed genes or by visible traits, for instance, hair colour or type, eye colour, body shape, and height. It depends on the genotype but is also influenced by environmental factors. 3 DIFFERENCE BETWEEN GENOTYPE AND PHENOTYPE Following are the important difference between genotype and phenotype. Genotype Phenotype The hereditary information of the organism is in the form The characteristics of an organism which are visible are of genes in the DNA and remains the same throughout known as phenotypes. the life. The same genotype produces the same phenotype. The same phenotype may or may not belong to the same genotype. Present inside the body as genetic material. Expression of genes as the external appearance. The genotype is inherited from the parent to the The phenotype is not inherited from the parent. offspring. It can be determined by scientific methods such as the It can be determined by observing the organism. polymerase chain reaction. It is affected by genes. It is affected by genotype and environmental conditions. For e.g., Blood group, eye colour, height, and genetic For e.g., Weight, physique, and beak of birds diseases. 4 2 2/13/2024 Chromosome, gene and allele Alleles are different forms of same gene. Genes are linearly arranged on chromosomes. Chromosomes contain genetic material of cell i.e. DNA. So chemically alleles, genes, chromosomes are all DNA ! 5 homozygosity and heterozygosity Homozygosity is the condition of having two identical alleles at a locus Heterozygosity describes a single gene having two different alleles. An individual is called homozygous for the trait when the two alleles of its genotype are identical (e.g. AA or aa). An organism that is homozygous for the recessive Allele only expresses recessive traits. Alternatively, if the two alleles are different in the genotype (e.g. Aa), the individual is called heterozygous. In heterozygous individuals, the only allele that is expressed is the dominant trait. The recessive allele is present, but its expression is hidden. 6 3 2/13/2024 homozygosity and heterozygosity Key Points If the two alleles are identical, the individual is called homozygous for the trait; if the two alleles are different, the individual is called heterozygous. Dominant alleles are expressed exclusively in a heterozygote, while recessive traits are expressed only if the organism is homozygous for the recessive allele. 7 homozygosity and heterozygosity Homozygous: of an organism in which both copies of a given gene have the same allele Heterozygous: of an organism which has two different alleles of a given gene Recessive: able to be covered up by a dominant trait Dominant: a relationship between alleles of a gene, in which one allele masks the expression (phenotype) of another allele at the same locus Allele: different types of the same gene on a chromosome Genotype: the characteristics coded for by alleles 8 4 2/13/2024 What is Continuous variation vs disContinuous variation in genetiCs? Variations are classified either as continuous, or quantitative (smoothly grading between two extremes, with the majority of individuals at the centre, as height varies in human populations); or as discontinuous, or qualitative (composed of well-defined classes, as blood groups vary in humans). Variation Variation is all the differences that exist in a population of the same species. These differences are caused by: Genetic variation - these are differences between individuals that are inherited from parents, such as the colour of your eyes, hair and skin. Environmental variation - these are differences between individuals that are not inherited but caused by the environment that the organism lives in, including scars and tattoos. Genetic and environmental variation - differences between individuals that are caused by both genetic and environmental factors, such as height and weight. 9 What is Continuous variation vs disContinuous variation in genetiCs? Continuous variation Surveys of continuous variation give us results that come in a range. Human height is an example of continuous variation. It ranges from that of the shortest person in the world to that of the tallest person. Any height is possible between these values, so this is continuous variation. For example, you can be 150 cm tall, 151 cm tall, or any height in between this - if you had a ruler that could measure small enough values. So, a characteristic that changes gradually over a range of values shows continuous variation. Examples of such characteristics are: height arm span weight Results from surveys of continuous variation are presented in line graphs or bar charts with a line of best fit drawn through them. If you record the heights of a group of people and draw a graph of your results, it usually looks something like this: 10 5 2/13/2024 What is Continuous variation vs disContinuous variation in genetiCs? Normal distribution Surveys of continuous variation often give us results in a characteristic shape seen in the green line on the graph above. If there are fewer readings at either ends of the scale and far more in the middle, we see a bellshaped graph of normal distribution. The more people you measure and the smaller the categories you use, the closer the results will be to this shape Figure caption, A bar chart to represent variation in height 11 What is Continuous variation vs disContinuous variation in genetiCs? Discontinuous variation Surveys of discontinuous variation give us values that come in groups rather than a range. Human blood groups are an example of discontinuous variation. In the ABO blood group system, only four blood groups are possible - A, B, AB or O. You cannot have a blood group in between these four groups, so this is discontinuous variation. Here are some examples: blood group eye colour Results from surveys of discontinuous variation are presented in charts. These is no line of best fit drawn because the values on the x-axis - blood groups in the graph below - could be placed in any order. If you record the blood groups of a group of people and draw a graph of your results, it usually looks something like this: 12 6 2/13/2024 What is Continuous variation vs disContinuous variation in genetiCs? Figure caption, A bar chart to represent the frequency of each blood group in the population 13 What is Continuous variation vs disContinuous variation in genetiCs? More examples 14 7 2/13/2024 What is Continuous variation vs disContinuous variation in genetiCs? 15 Mendels laws of inheritance Inheritance can be defined as the process of how a child receives genetic information from the parent. The whole process of heredity is dependent upon inheritance and it is the reason that the offsprings are similar to the parents. This simply means that due to inheritance, the members of the same family possess similar characteristics. It was only during the mid 19th century that people started to understand inheritance in a proper way. This understanding of inheritance was made possible by a scientist named Gregor Mendel, who formulated certain laws to understand inheritance known as Mendel’s laws of inheritance. 16 8 2/13/2024 Why Was Pea Plant seleCted for mendel’s exPeriments? He selected a pea plant for his experiments for the following reasons: 1. The pea plant can be easily grown and maintained. 2. They are naturally self-pollinating but can also be cross-pollinated. 3. It is an annual plant, therefore, many generations can be studied within a short period of time. 4. It has several contrasting characters. Mendel conducted 2 main experiments to determine the laws of inheritance. These experiments were: 1. Monohybrid Cross 2. Dihybrid Cross While experimenting, Mendel found that certain factors were always being transferred down to the offspring in a stable way. Those factors are now called genes i.e. genes can be called the units of inheritance. 17 mendel’s exPeriments Mendel experimented on a pea plant and considered 7 main contrasting traits in the plants. Then, he conducted both experiments to determine the inheritance laws. A brief explanation of the two experiments is given below. Monohybrid Cross In this experiment, Mendel took two pea plants of opposite traits (one short and one tall) and crossed them. He found the first generation offspring were tall and called it F1 progeny. Then he crossed F1 progeny and obtained both tall and short plants in the ratio Mendel even conducted this experiment with other contrasting traits like green peas vs yellow peas, round vs wrinkled, etc. In all the cases, he found that the results were similar. From this, he formulated the laws of Segregation And Dominance. Dihybrid Cross In a dihybrid cross experiment, Mendel considered two traits, each having two alleles. He crossed wrinkledgreen seed and round-yellow seeds and observed that all the first generation progeny (F1 progeny) were round-yellow. This meant that dominant traits were the round shape and yellow colour. 18 9 2/13/2024 mendel’s exPeriments He then self-pollinated the F1 progeny and obtained 4 different traits: round-yellow, round-green, wrinkledyellow, and wrinkled-green seeds in the ratio 9:3:3:1. After conducting research for other traits, the results were found to be similar. From this experiment, Mendel formulated his second law of inheritance i.e. law of Independent Assortment. 19 Mendels laws of inheritance 20 10 2/13/2024 mendel’s exPeriments Conclusions from Mendel’s Experiments The genetic makeup of the plant is known as the genotype. On the contrary, the physical appearance of the plant is known as phenotype. The genes are transferred from parents to the offspring in pairs known as alleles. During gametogenesis when the chromosomes are halved, there is a 50% chance of one of the two alleles to fuse with the allele of the gamete of the other parent. When the alleles are the same, they are known as homozygous alleles and when the alleles are different they are known as heterozygous alleles. Mendel’s laws The two experiments lead to the formulation of Mendel’s laws known as laws of inheritance which are: 1. Law of Dominance 2. Law of Segregation 3. Law of Independent Assortment 21 22 11 2/13/2024 23 dominant and reCessive: Have you ever wondered why some people have blue or brown eyes? The coloring of the blue and brown eyes is an example of different versions of a gene. Different versions of a gene are called alleles. Alleles can be considered dominant or recessive, with dominant being the trait that is observed or shown and recessive being the trait is not seen. Dominant alleles are seen as an uppercase of a letter; for example, B. Recessive alleles are seen as a lower case of a letter; b. In order for a person to show the dominant trait, one of the person’s parents must have the dominant trait (which is an uppercase letter). Remember that human cells carry 2 copies of each chromosome, one from the biological mother’s genes and one from the biological father’s genes. With that being said, there are 2 sets of alleles that can be dominant or recessive. If a person carries a heterozygous set of alleles (both uppercase and lower case letter of the gene) then the person will show the dominant trait (being that there is an uppercase letter present). 24 12 2/13/2024 dominant and reCessive: For example, the brown eye allele is dominant, B. You would need at least one copy of the brown eye allele (B) to have brown eyes. When you have two copies of the alleles that are both dominant, this is called codominance. For example, if the dominant trait is red for flowers and another dominant trait is white, then the flower will have both red and white as the dominant traits are expressed equally. If a person carries two copies of the brown eye allele, since they are codominant, the person would have brown eyes. Recessive alleles are the genes that do not show the trait. If a person has one copy of the brown eye allele (dominant) and one copy of the blue eye allele (recessive) then that person is considered to be a carrier of the blue eye allele, since they would have brown eyes but still have the blue eye trait that is not shown. Recessive alleles only show the traits if the person has 2 copies of the same alleles. This is considered being homozygous, having the same 2 copies of alleles. If a person has 2 copies of the blue eye allele (both recessive) then the person would have blue eyes. 25 dominant and reCessive: Illustration to show the inheritance of dominant and recessive alleles for eye colour. Image credit: Genome Research Limited 26 13 2/13/2024 dominant and reCessive: Sex-linked genes are genes that are inhererited through the X chromosome. Remember that a biological female carries 2 sets of X chromosomes (XX) and a biological male carries one set of the X and one set of Y chromosomes (XY). If the offspring is a boy, the X chromosome comes from the mother and the Y comes from the father. If the offspring is a girl, one of the X chromosomes comes from the mother and the other X chromosome comes from the father. In some genetic diseases that are caused by sex-linked genes, for example haemophila, a color blindness trait, the allele for the disease is recessive. You can recall that recessive traits are only shown if they are homozygous (both copies of the alleles are recessive). For a female to have the disease, both of her X chromosomes must carry the recessive diseased copies of alleles. For a male to have a sex-linked gene, only one copy of the recessive sex-linked gene is needed for the male to have the disease. Dominance does not matter in sex-linked genes for XY males. If the mother is a carrier (unaffected but still have the affected trait), her offspring could be affected. Males are more likely to inherit a sex-linked gene as only one chromosome of a diseased trait is needed, whether the disease trait is dominant or recessive. 27 dominant and reCessive: You can see that sex-linked genes are by chance. Even though the father is affected with a dominant trait, only half of their offspring is affected, especially from the girls because they have to inherit a chromosome from the father. The male offspring was unaffected because they had already received a Y chromosome from the father so they got the non affected X chromosome form the mother. In this photo, the mother is affected with a dominant trait but only half of their offspring was able to be affected. The offsprings had a 50% chance of getting the affected trait. With an unaffected mother whose carrier, meaning the disease trait is recessive, only one of the offspring was affected and one is unaffected but a carrier. This is an example of how dominance genes does not matter as it depends on which X chromosome you can get and whether or not the set chromosomes you inherited contain the diseased trait being dominant or recessive. With males especially, they would only get a 50/50 chance of inheriting a non diseased trait, as they can only get the X chromosome from the mother. With females, they have a lower chance of getting a diseased trait as it depends on what chromosome she inherited from the mother whether its dominant or recessive and what X chromosome she inherited from her father. 28 14 2/13/2024 dominant and reCessive: X-linked gene inheritance. The expression of recessive X-linked genes is more common in boys who only have one X gene. 29 autosomal and sex Chromosome: Solution 1. Autosomes are the chromosomes that determine somatic characters such as body weight, length, etc. of an organism. 2. Sex Chromosomes are the chromosomes that determine sex and sex-related hormonal traits. Autosomes 1-Determining somatic characters mainly involves the growth of an organism. 2. All chromosomes are of the same size, that is, homologous. 3. Follows Mendelian Inheritance. 4. In humans, 22 pairs of autosomes are present. Sex chromosomes 1. Determines the gender and sexrelated traits. 2. Chromosomes are partially homologous. 3. Shows Non-mendelian inheritance. 4. In humans, only one pair of chromosomes is present. 30 15 2/13/2024 dominant and reCessive: The human genome is organized into 23 pairs of chromosomes (22 pairs of autosomes and one pair of sex chromosomes), with each parent contributing one chromosome per pair. The X and Y chromosomes, also known as the sex chromosomes, determine the biological sex of an individual: females inherit an X chromosome from the father for a XX genotype, while males inherit a Y chromosome from the father for a XY genotype (mothers only pass on X chromosomes). The presence or absence of the Y chromosome is critical because it contains the genes necessary to override the biological default - female development - and cause the development of the male reproductive system. Sex-linked, as related to genetics, refers to characteristics (or traits) that are influenced by genes carried on the sex chromosomes. In humans, the term often refers to traits or disorders influenced by genes on the X chromosome, as it contains many more genes than the smaller Y chromosome. Males, who have only a single copy of the X chromosome, are more likely to be affected by a sex-linked disorder than females, who have two copies. In females, the presence of a second, non-mutated copy may cause different, milder, or no symptoms of a sex-linked disorder. 31 dominant and reCessive: X-linked, as related to genetics, refers to characteristics or traits that are influenced by genes on the X chromosome. Humans and most other mammals have two sex chromosomes, X and Y. Females have two X chromosomes in their cells, while males have one X and one Y. In the case of an X-linked disease, it is usually males that are affected because they have a single copy of the X chromosome that carries the diseasecausing mutation. In females, the presence of a second, non-mutated copy may cause different, milder, or no symptoms of a sex-linked disorder. 32 16 2/13/2024 dominant and reCessive: Sex-linked character an observable feature of an organism controlled by the genes on the chromosomes that determine the organism’s sex. Each individual has a pair of sex chromosomes; one member of the pair is inherited from each parent. 33 34 17