Heredity and Evolution PDF

# Heredity and Evolution ## Genetics * Branch of science that deals with heredity and variation. * Also known as genetics. ## Heredity * **It means the transmission of features/characters/traits from one generation to the next generation.** ## Variation * **The differences among the individual...

# Heredity and Evolution ## Genetics * Branch of science that deals with heredity and variation. * Also known as genetics. ## Heredity * **It means the transmission of features/characters/traits from one generation to the next generation.** ## Variation * **The differences among the individuals of a species of a population are called variations.** ## Genotype * **The complete set of genes in an organism's genome is called genotype.** ## Phenotype * **The observable characters in an organism make the phenotype. Phenotype is a modified genotype and many of the phenotypes cannot be inherited.** ## Clones * **Organisms which are exact copies of each other.** ## Mendel's Work * **Gregor Johann Mendel, known as 'Father of Genetics', was an Austrian monk who worked on pea plants to understand the concept of heredity.** * **His work laid the foundation of modern genetics.** * **He made Law of dominance, Law of segregation, Law of independent assortment.** ## Plant Selected by Mendel * **Pisumsativum (garden pea). Mendel used a number of contrasting characters for garden pea.** ## Mendel's Experiment * **He conducted a series of experiments in which he crossed the pollinated plants to study character (at a time).** ## Cross between two pea plants with one pair of contrasting character is called a monohybrid cross. ### Monohybrid Cross | | Parent | Allelic pair of genes | Gametes | F1 Generation | Self pollination of F1 gametes | F2 Generation | |---|---|---|---|---|---|---| | Tall Plant | T T | - | T, T | Tt | Tt x Tt | TT, Tt, Tt, tt | | X | Dwarf Plant | tt | t, t | All tall plants | | | | Gamete | T | | t | | T, t | - | | | | | | | T, t | - | | | | | | | | Gamete: T, t | | | | | | | | | | | | | | | | TT - tall | | | | | | | | Tt - tall | | | | | | | | Tt - tall | | | | | | | | tt - dwarf | * **Phenotypic ratio -> 3:1** * **Genotypic ratio -> 1:2:1** ### Observation of Monohybrid Cross 1. **All F1 progeny were tall (no medium height plant).** 2. **F2 progeny 1/4 were short, 3/4 were tall.** 3. **Phenotypic ratio F2 - 3:1 (3 tall : 1 short).** * **Genotypic ratio F2 - 1:2:1.** ## Conclusion of Mendel's Experiment 1. **TT and Tt both are tall plants while tt is a short plant.** 2. **A single copy of T is enough to make the plant tall, while both copies have to be ‘t’ for the plant to be short.** 3. **Characters/Traits like ‘T’ are called dominant trait and ‘t’ are recessive trait.** ## Law of Segregation * **Every organism possesses a pair of alleles for a particular trait. During gamete formation, a gamete receives only one trait from the alleles.** * **A particular trait can be dominant or recessive.** ## Dihybrid Cross * **A cross between two plants having two pairs of contrasting characters.** * **Parent: Round, green seeds x Wrinkled, Yellow seeds.** * **Gametes: RRYY, rryy.** | | F1 | Selfing F1 gametes | F2 gametes | |---|---|---|---| | | RrYy | RrYy x RrYy | RY, Ry, rY, ry | | | | | | | | RY | Ry | rY | ry | |---|---|---|---|---| | **RY** | RRYY | RRYy | RrYY | RrYy | | **Ry** | RRYy | RRyy | RrYy | Rryy | | **rY** | RrYY | RrYy | rrYY | rrYy | | **ry** | RrYy | Rryy | rrYy | rryy | * **Phenotypic ratio: ** * **Round, yellow: 9** * **Round, green: 3** * **Wrinkled, yellow: 3** * **Wrinkled, green: 1** ## Conclusion: 1. **Round and yellow seeds are dominant characters.** 2. **Occurrence of new phenotypic combinations show that genes for round and yellow seeds are inherited independently.** ## Law of Independent Assortment * **Alleles of different characters separate independent from each other during gamete formation.** ## Sex Determination * **Determination of sex of an offspring.** * **Factors: Environment and Genetic.** ### Environment * **In some animals the temperature at which the fertilized eggs are kept decide the gender. Eg: in Turtle.** ### Genetic * **In some animals like humans gender is determined by a pair of chromosomes called sex chromosomes.** ## Sex Chromosomes * **In human beings there are 23 pairs of chromosomes. Out of these 22 chromosomes pairs are called autosomes and the last pair of chromosome that help in deciding gender of that individual is called sex chromosomes.** * **XX - female** * **XY - male.** * **All children will inherit an X chromosome from their mother whether they are boy or girl. Thus sex of children will be determined by what they inherit from their father.**