Genetics of Coat Color in Mice

Basic Genetics and Coat Color Alleles

• Alleles:
  • b1: Black coat color, dominant
  • b2: White coat color, recessive
• Genotypes and Phenotypes:
  • Homozygous b1 (b1/b1) results in black coat
  • Homozygous b2 (b2/b2) results in white coat
  • Heterozygous (b1/b2) results in black coat (due to dominance of b1)

Crossing Black and White Mice

• Individuals:
  • Black individual (female, homozygous b1/b1)
  • White individual (male, homozygous b2/b2)
• Gamete Production:
  • Meiosis results in gametes carrying single alleles
  • Black individual produces gametes with b1 allele
  • White individual produces gametes with b2 allele
• Fertilization:
  • All progeny are heterozygous (b1/b2), resulting in black coat color

Pure Breeding Population

• Characteristics:
  • Individuals are homozygous for the same allele
  • Crossing any two individuals produces progeny with the same genotype and phenotype as parents
  • Known as a "pure breeding" population

Product Rule in Genetics

• Definition:
  • If two independent events occur, the probability of both occurring is the product of their individual probabilities
• Example:
  • Probability of two heads in coin toss = 1/2 * 1/2 = 1/4

Monohybrid Cross

• Definition:
  • Cross between two heterozygotes for a single trait
• Example with Mice:
  • Both mice are b1/b2 and black in color
  • Punnett Square Analysis:
    • Gametes: 50% b1, 50% b2
    • Possible progeny genotypes:
      • b1/b1 (homozygous black)
      • b1/b2 (heterozygous black)
      • b2/b2 (homozygous white)
    • Genotypic Ratio: 1:2:1 (b1/b1 : b1/b2 : b2/b2)
    • Phenotypic Ratio: 3:1 (black : white)

Key Concepts

• Monohybrid cross produces a 3:1 phenotypic ratio favoring the dominant allele
• Useful for determining dominance and recessiveness in genetic traits