Govt. Exams
Entrance Exams
The carrier mother (XᴮXᵇ) × normal father (XᴮY) produces sons with 50% probability of being XᵇY (color blind), as sons receive Xᵇ from mother in half the cases.
In a dihybrid cross, the 9:3:3:1 ratio indicates that 9 out of 16 offspring have dominant phenotypes for both traits (A_B_). This represents 9/16 probability.
With 20 map units distance, recombination frequency is 20%. Parental types (AB/ab) = 40% each, recombinants = 10% each. AaBb from coupling = 40 out of 160.
Cross: ww × w⁺Y produces w⁺w (heterozygous females with red eyes) and wY (white-eyed males). F1 females are red-eyed.
Cross: XʰY × XʰXʰ produces XʰXʰ (carrier daughters) and XʰY (normal sons). Daughters carry one recessive allele but are phenotypically normal.
Huntington's disease is an autosomal dominant disorder. A single copy of the dominant allele causes the disease phenotype.
Cross: Aa × Aa produces AA (25%), Aa (50%), aa (25%). Only homozygous recessive (aa) individuals have cystic fibrosis.
If two tall plants produce short offspring, both parents must be heterozygous (Aa). The short offspring (aa) proves tall is dominant.
Linked genes are located close together on the same chromosome and tend to be inherited together, violating the Law of Independent Assortment.
A mutation is any sudden, spontaneous change in the DNA sequence that can be inherited. It provides genetic variation for natural selection.
