Govt Exams
For AaBb × AaBb, probability of aa = 1/4 and bb = 1/4. Combined probability = 1/4 × 1/4 = 1/16.
Hardy-Weinberg equilibrium states that allele frequencies remain constant when no evolutionary forces (mutation, selection, migration, genetic drift) act on a population.
Mutations in non-coding regions vary in importance. Those in regulatory elements (promoters, enhancers) can be significant; most others are neutral.
For X-linked traits in males (hemizygous), allele frequency equals phenotype frequency. In females at equilibrium, the allele frequency is the same as in males: 0.1
Bottlenecks drastically reduce population size, increasing genetic drift. Random allele loss occurs, reducing genetic variation and increasing chance of fixation.
Darwin's finches underwent adaptive radiation, diverging from a common ancestor into multiple species with different beak morphologies adapted to different food sources.
Cross: AS × AS produces AA (unaffected, 1/4), AS (carrier, 1/2), SS (affected, 1/4). Probability of unaffected = 1/4 + 1/2 = 3/4 = 0.75
If one dominant homozygous class (AABB, AABb, or AAbb) is lethal, the 9:3:3:1 ratio adjusts accordingly. Common outcome is 9:3:4 when one class is removed.
Lower recombinant frequencies indicate genes are linked but can undergo crossing over, producing recombinants at lower frequencies than parentals.
Gene flow (migration) introduces alleles from one population to another, counteracting genetic drift and maintaining genetic variation.