In a dihybrid cross (AaBb × AaBb), what is the expected phenotypic ratio in F2?
Answer: B
The classical dihybrid cross ratio is 9:3:3:1, following Mendel's Law of Independent Assortment for two independently assorting genes.
Q.2Medium
What is the term for genes located on the X chromosome?
Answer: B
Sex-linked genes are located on sex chromosomes, particularly the X chromosome. X-linked traits show different inheritance patterns in males and females.
Q.3Medium
Color blindness in humans is an X-linked recessive trait. If a carrier female (XᶜX) marries a normal male (XᶜY), what percentage of their sons will be color blind?
Answer: C
Cross: XᶜX × XᶜY produces: XᶜXᶜ (normal daughter), XᶜX (carrier daughter), XᶜY (color blind son), XᶜY (normal son). 50% of sons are color blind.
Q.4Medium
Which of the following is an example of incomplete dominance?
Answer: B
Incomplete dominance occurs when the heterozygote shows an intermediate phenotype. Red × white flowers → pink flowers is a classic example.
Q.5Medium
What is codominance?
Answer: B
In codominance, both alleles contribute equally to the phenotype. Example: AB blood group where both A and B antigens are expressed.
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Q.6Medium
ABO blood group system in humans shows which type of inheritance?
Answer: C
ABO blood groups show codominance. Alleles Iᴬ and Iᴮ are dominant over i but are codominant to each other, producing four blood types.
Q.7Medium
Which of the following best describes a mutation?
Answer: B
A mutation is any sudden, spontaneous change in the DNA sequence that can be inherited. It provides genetic variation for natural selection.
Q.8Medium
Linkage is the phenomenon where genes are inherited together because they are located on the same ______.
Answer: C
Linked genes are located close together on the same chromosome and tend to be inherited together, violating the Law of Independent Assortment.
Q.9Medium
A plant breeder crosses two tall pea plants and obtains both tall and short offspring. This indicates that tall is _______ over short.
Answer: C
If two tall plants produce short offspring, both parents must be heterozygous (Aa). The short offspring (aa) proves tall is dominant.
Q.10Medium
In humans, if both parents are carriers of cystic fibrosis (Aa), what is the probability their child will have the disease (aa)?
Answer: A
Cross: Aa × Aa produces AA (25%), Aa (50%), aa (25%). Only homozygous recessive (aa) individuals have cystic fibrosis.
Q.11Medium
Which type of genetic disorder shows autosomal dominant inheritance?
Answer: B
Huntington's disease is an autosomal dominant disorder. A single copy of the dominant allele causes the disease phenotype.
Q.12Medium
In a dihybrid cross between two heterozygous pea plants (AaBb × AaBb), what is the probability of obtaining an offspring with at least one dominant trait for both genes?
Answer: A
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 169 probability.
Q.13Medium
A woman with normal vision (carrier for color blindness) marries a man with normal vision. What percentage of their sons will be color blind?
Answer: C
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.
