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[Audio] Mendel's Laws of Inheritance with Cross Diagrams Gregor Mendel proposed three fundamental laws of inheritance based on his experiments with pea plants. These laws explain how traits are passed from parents to offspring. 1. Law of Dominance Definition: When two different alleles are present, the dominant allele masks the expression of the recessive allele in the first generation (F₁). Example: Flower Color in Pea Plants Dominant allele (P) = Purple Recessive allele (p) = White Cross Diagram: Monohybrid Cross (P-Generation) P P p Pp (Purple) Pp (Purple) p Pp (Purple) Pp (Purple) F₁ Generation: 100% Purple (Pp) (Dominant allele masks the recessive) 2. Law of Segregation Definition: During gamete formation, the two alleles for a gene separate (segregate), and each gamete carries only one allele. Example: F₁ Hybrid Cross (Self-pollination of Heterozygous Purple Plants, Pp) Cross Diagram: Segregation in F₂ Generation P p P PP (Purple) Pp (Purple) p Pp (Purple) pp (White) F₂ Generation Results: Phenotypic Ratio → 3:1 (3 Purple : 1 White) Genotypic Ratio → 1:2:1 (PP : Pp : pp) Recessive trait (White) reappears in F₂ due to allele segregation. 3. Law of Independent Assortment Definition: Genes for different traits assort independently during gamete formation. The inheritance of one trait does not affect the inheritance of another..
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[Audio] Example: Dihybrid Cross (Seed Shape & Seed Color) R = Round (Dominant), r = Wrinkled (Recessive) Y = Yellow (Dominant), y = Green (Recessive) Cross Diagram: Dihybrid Cross (F₁ Generation Cross RrYy × RrYy) RY Ry rY ry RY RRYY (Round, Yellow) RRYy (Round, Yellow) RrYY (Round, Yellow) RrYy (Round, Yellow) Ry RRYy (Round, Yellow) RRyy (Round, Green) RrYy (Round, Yellow) Rryy (Round, Green) rY RrYY (Round, Yellow) RrYy (Round, Yellow) rrYY (Wrinkled, Yellow) rrYy (Wrinkled, Yellow) ry RrYy (Round, Yellow) Rryy (Round, Green) rrYy (Wrinkled, Yellow) rryy (Wrinkled, Green) F₂ Generation Results: Phenotypic Ratio → 9:3:3:1 9 Round, Yellow 3 Round, Green 3 Wrinkled, Yellow 1 Wrinkled, Green Confirms that seed shape and seed color assort independently Summary of Mendel's Laws Law Explanation Example Dominance Dominant traits mask recessive traits in F₁ Purple flower (P) dominates White (p) Segregation Alleles separate during gamete formation F₂ ratio: 3:1 (Purple:White) Independent Assortment Different traits are inherited separately Seed shape and seed color assort independently.