Which of the following is a correct statement about mature embryo sac organization in angiosperms?
Answer: A
Antipodal cells (typically three) are located at the chalazal end and are vegetative in nature, containing vacuoles for nutrient storage. They eventually degenerate.
Q.182Medium
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.183Medium
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.184Medium
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.185Medium
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.
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Q.186Medium
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.
Q.187Medium
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.188Medium
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.189Medium
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.190Medium
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.191Medium
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.192Medium
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.193Medium
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.194Medium
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.
Q.195Medium
The 10% law of energy transfer in an ecosystem states that only 10% of energy is transferred to the next trophic level. What happens to the remaining 90%?
Answer: B
The remaining 90% energy is lost through cellular respiration, heat dissipation, and decomposition processes at each trophic level, which is why ecosystems have fewer organisms at higher trophic levels.
Q.196Medium
The concept of 'ecological niche' refers to:
Answer: B
An ecological niche encompasses the organism's habitat, food, behavior, and role in the ecosystem - essentially its complete functional position in the environment.
Q.197Medium
Which of the following is a characteristic of r-selected species?
Answer: B
r-selected species (like rabbits and insects) have high reproductive rates, short generation times, and invest little in individual offspring care, prioritizing quantity over quality.
Q.198Medium
The carrying capacity of an environment is best defined as:
Answer: A
Carrying capacity (K) is the maximum population size that an environment can sustain indefinitely given available resources and environmental resistance.
Q.199Medium
In India's biodiversity hotspots, which region is NOT included in the recognized biodiversity hotspots?
Answer: D
India has 4 recognized biodiversity hotspots: Western Ghats, Indo-Burma, Himalayas, and Sundaland. Eastern plains are not recognized as a separate hotspot.
Q.200Medium
The concept of 'biomagnification' refers to:
Answer: B
Biomagnification is the process where toxic pollutants (like DDT, mercury) accumulate in higher concentrations in organisms at higher trophic levels due to bioaccumulation.
