5.2 Basic Principles of Heredity SV
Basic Principles of Heredity
Mendel's Experimental Design: Utilized controlled breeding in pea plants, preventing self-fertilization by removing anthers for cross-pollination, which allowed for observation of distinct traits.
Monohybrid Crosses: Began with homozygous round (RR) and wrinkled (rr) seeds. F1 generation (Rr) showed round seeds, leading to a 3:1 phenotypic ratio in F2 generation with 5474 round vs 1850 wrinkled seeds.
Mendel's Conclusions: Proposed four principles:
Traits are coded by pairs of factors (alleles) that segregate.
Dominance and recessivity determine traits in phenotypes.
Genes segregate randomly into gametes.
Each organism has two alleles that segregate during gamete production (Law of Segregation).
Genetics in Meiosis: Alleles segregate during anaphase I of meiosis.
Genotypic and Phenotypic Ratios: Example ratios from crosses (e.g., Aa × Aa gives 3:1 phenotypic ratio).
Test Cross: Used to determine if an organism is homozygous or heterozygous for a trait.
Mendel’s Second Law: Independent assortment of different traits occurs during gamete formation.
Dihybrid Crosses: Examines two traits with a 9:3:3:1 phenotypic ratio.
Probability in Genetics: Incorporates multiplication and addition rules for predicting genetic outcomes.