Genetic Diagrams and Punnett Squares

Introduction to Genetic Diagrams

• Genetic diagrams depict possible allele combinations from two parents.
• Alleles are shown as letters:
  • Capital letter: Dominant allele (e.g., A)
  • Lowercase letter: Recessive allele (e.g., a)

Example Scenario

• Gene: Determines muscle type in mice
  • Dominant Allele (A): Normal muscle
  • Recessive Allele (a): Muscular

Steps to Draw a Genetic Diagram

1. Identify Parent's Phenotype and Genotype
   • Given in the question.
   • Homozygous normal mouse: Genotype AA (Phenotype: Normal)
   • Homozygous muscular mouse: Genotype aa (Phenotype: Muscular)
2. Determine Gametes' Genotypes
   • Split parent genotypes into two alleles.
   • Represents cells splitting in meiosis.
3. Find Offspring's Genotypes and Phenotypes
   • Combine all possible gametes.
   • Example result: All offspring heterozygous (Aa) with normal phenotype.

Punnett Squares

• 2x2 grid showing allele combinations.
• Simplifies the genetic diagram process.
• Does not explicitly show phenotypes.

Using Punnett Squares

• Repeat of the heterozygous mouse mating example:
  • Place gametes on top and left of the grid.
  • Fill squares to determine offspring genotypes:
    • 1 AA (homozygous dominant)
    • 2 Aa (heterozygous)
    • 1 aa (homozygous recessive)

Phenotype Ratios and Probabilities

• Example Ratios:
  • 3:1 ratio of normal to muscular mice
• Example Probabilities:
  • 25% chance of muscular offspring

Interaction of Genes and Environment

• Traits can be influenced by multiple genes and environmental factors.
• Example: Genetic potential for height can be affected by nutrition and sleep.

Conclusion

• Reminder that genetic diagrams and Punnett squares are tools to predict possible genetic outcomes.
• External factors can also influence genetic traits.

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Note: Always consider both genetic and environmental influences when studying inheritance patterns.