Genetics Lecture Notes

Key Concepts

• Alleles: Variants of genes; two types for each trait
  • Dominant Allele: Represented by a capital letter (e.g., B for brown eyes)
  • Recessive Allele: Represented by a lowercase letter (e.g., b for blue eyes)

Genotype vs. Phenotype

• Genotype: The genetic makeup of an individual (e.g., BB, Bb, bb)
• Phenotype: The observable physical characteristics (e.g., brown eyes, blue eyes)

Types of Genotypes

• Homozygous Dominant: Two dominant alleles (e.g., BB)
• Heterozygous: One dominant and one recessive allele (e.g., Bb)
• Homozygous Recessive: Two recessive alleles (e.g., bb)

Punnett Squares

• Tool used to predict the probability of genotypes in offspring
• Monohybrid Cross: Focuses on one trait
• Dihybrid Cross: Focuses on two traits

Example Problems

1. Homozygous Wolf (bb) Mating with Heterozygous Wolf (Bb)

   • Punnett Square Setup:

   | | B | b | |---|---|---| | b | Bb | bb | | b | Bb | bb |

   • Probability of Blue Eyes (bb):
     • 2 out of 4 = 50%
   • Phenotypic Ratio: 1 blue : 1 brown
   • Genotypic Ratio: 1 Bb : 1 bb

2. Two Heterozygous Cats (Bb x Bb)

   • Punnett Square Setup:

   | | B | b | |---|---|---| | B | BB | Bb | | b | Bb | bb |

   • Probability of Brown Eyes:
     • 3 out of 4 = 75%
   • Probability of Homozygous:
     • 2 out of 4 = 50%
   • Phenotypic Ratio: 3 brown : 1 blue
   • Genotypic Ratio: 1 BB : 2 Bb : 1 bb

3. Incomplete Dominance in Flowers (R for Red, W for White)

   • Pink flower genotype: RW
   • Punnett Square for Pink Flowers (RW x RW):

   | | R | W | |---|---|---| | R | RR | RW | | W | RW | WW |

   • Probability of Red Flower:
     • 1 out of 4 = 25%
   • Probability of Pink Flower:
     • 2 out of 4 = 50%
   • Probability of White Flower:
     • 1 out of 4 = 25%

4. Two Traits (Fur Color and Eye Color)

   • Example: Black Fur (F) and Blue Eyes (b) vs. White Fur (f) and Brown Eyes (B)
   • Dihybrid Cross Setup:
   • Punnett Square:
   • Probability calculations for combinations of traits

Summary of Probabilities

• Different combinations of traits yield various probabilities and ratios
  • Probability calculations can be summarized for phenotype and genotype ratios

Conclusion

• Understanding how to set up and interpret Punnett squares is essential for predicting genetic outcomes.