Genetics Lecture: Laws of Inheritance

Introduction

• Continuation of genetics
• Focus: Rules/laws of inheritance
• Connection between laws and chromosome behavior during meiosis
• Pedigree analysis and human traits/diseases

Pedigree Symbols

• Open box: Unaffected male
• Open circle: Unaffected female
• Shaded symbol: Affected individual

Phenylketonuria (PKU)

• Example of autosomal recessive inheritance
• Mutation in enzyme processing phenylalanine
• Affects diet management
• Skips multiple generations; appears due to inbreeding

Color Blindness

• Example of sex-linked recessive inheritance
• Affects males predominantly
• Skips generations; passed from grandfather to grandsons

Mendel's Work

Mendel's Theory

• Studies with pea plants
• Self-pollination vs cross-pollination
• Traits with clear dominant/recessive phenotypes
• Pure breeding lines: homozygous allele composition

Mendel's Experiments

• Monohybrid Cross: Demonstrates basic inheritance (3:1 ratio)
• Dihybrid Cross: Demonstrates independent assortment (9:3:3:1 ratio)

Mendel's Laws

1. Law of Segregation
   • Each adult has a pair of alleles for a trait
   • Alleles segregate during gamete formation
   • Explains PKU inheritance pattern
2. Law of Independent Assortment
   • Traits assort independently if not linked
   • Alignments of chromosomes during meiosis are random

Sex-Linked Inheritance

• Thomas Hunt Morgan's Work
  • Focus on fruit flies, eye color mutation
  • Mutation leads to white eyes, sex-linked trait
• Chromosomes
  • X and Y chromosomes in flies/humans
  • Red eyes dominant over white eyes in fruit flies

Experimental Crosses

• Crosses similar to Mendel's experiments
• White-eyed male x red-eyed female:
  • F1: All red-eyed progeny
  • F2: 3:1 ratio, but all white-eyed are male
• Parallel to human color blindness

Conclusion

• Think about reciprocal crosses and their outcomes
• Prepare for discussion on first genetic map and its significance in next lecture

• Note: Consider the implications of the reciprocal cross and differences between Mendel's and sex-linked inheritance.