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.
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.
ABO blood groups show codominance. Alleles Iᴬ and Iᴮ are dominant over i but are codominant to each other, producing four blood types.
In codominance, both alleles contribute equally to the phenotype. Example: AB blood group where both A and B antigens are expressed.
Incomplete dominance occurs when the heterozygote shows an intermediate phenotype. Red × white flowers → pink flowers is a classic example.
