Variation & Mutation

Sources of genetic diversity, mutation types, and Hardy–Weinberg equilibrium

Chapter Summary

Genetic variation arises from mutation, recombination, and random mating. Mutation types include point, frameshift, and chromosomal. Population genetics models (Hardy–Weinberg) predict allele frequencies under ideal conditions.

Mutation Types

  • Point Mutations: single-base substitutions (silent, missense, nonsense)
  • Frameshift Mutations: insertions/deletions altering reading frame
  • Chromosomal Mutations: deletions, duplications, inversions, translocations
Mutation Types

Nondisjunction

Failure of chromosome pairs to separate during meiosis I or II → gametes with abnormal chromosome numbers (aneuploidy). Example: Trisomy 21 (Down syndrome) results from nondisjunction of chromosome 21.

Nondisjunction

Sources of Genetic Diversity

  • Crossing Over: exchange of segments between homologous chromosomes in Prophase I
  • Independent Assortment: random alignment of homologs at Metaphase I
  • Random Fertilization: random union of gametes
Sources of Diversity

Hardy–Weinberg Calculator

Enter allele frequency p (dominant); q = 1 − p:

Key Terms

Quiz Yourself

1. A deletion of one base causes:



2. Trisomy 21 results from:



3. In Hardy–Weinberg, q = 1 − p. If p = 0.7, q = ___.