Entrance Exams
Govt. Exams
Heterozygous frequency = 2pq = 2(0.7)(0.3) = 0.42. Expected heterozygous individuals = 0.42 × 500 = 210.
Directional selection occurs when one extreme phenotype has higher fitness. Dark beetles have selective advantage, shifting population toward darker phenotype.
Multiple lines of evidence support evolution: homologous structures indicate common ancestry, vestigial organs show evolutionary remnants, and fossil records show gradual changes over time.
Phenotypic plasticity is the ability of a single genotype to produce different phenotypes in response to environmental variation (e.g., hydrangea flower color).
Natural selection is the non-random differential reproduction of organisms with traits that increase fitness. Organisms with advantageous traits leave more offspring.
Silent mutation occurs in the third position of a codon and does not change the amino acid due to degeneracy of genetic code. No phenotypic effect.
Mutation is a permanent change in the DNA sequence that can occur spontaneously or be induced. It is the source of genetic variation.
Cross: XᴮXᵇ × XᴮY produces sons: 50% XᴮY (normal) and 50% XᵇY (color blind). Therefore, 50% of sons are color blind.
Haemophilia A (clotting factor VIII deficiency) is X-linked recessive. Affected males (XᵃY) pass the allele to all daughters but no sons.
X-linked recessive traits show more affected males (XᵃY) than females because males need only one copy of recessive allele on their single X chromosome.