Principle of inheritance and variation practice · Mixed difficulty

Option A (3:1 ratio in ${F_2}$ generation) is correct because the 3:1 phenotypic ratio in the F2 generation of a monohybrid cross demonstrates the dominance of one allele over the other.

Option B (Recombination) is correct because recombination refers to the process that generates non-parental combinations of genes, often through crossing over.

Option B (Dominant) is correct because when a true-breeding yellow seed plant is crossed with a green seed plant, and all F1 plants have yellow seeds, it means yellow is dominant.

Option A (Single base DNA) is correct because a point mutation involves a change in a single base within the DNA sequence.

Option A (O and A) is correct because if the mother is O and the child is B, the father must have at least one B allele. Therefore, a father with only O and A alleles cannot be the father.

The correct answer is A (Four different types of gametes produced by the ${F_1}$-dihybrid) because a condition where a gene is present in only a single copy in a diploid cell is called hemizygous, which is observed in the gametes of an F1 dihybrid.

Option D (All the daughters will be green and all the sons will be pink) is correct because the green body colour gene is on the X chromosome and dominant, so daughters inherit the green gene from their father and the pink gene from their mother, resulting in green daughters. Sons inherit the Y chromosome from their father and the pink gene from their mother, resulting in pink sons.

Option D (incomplete dominance) is correct because in sickle cell anemia, heterozygotes (carriers) exhibit an intermediate phenotype, showing some sickling of red blood cells but not the full-blown disease.

Option D is correct because in hexaploid wheat (2n=6x=42), monosomic is 2n-1=41, haploid is n=21, nullisomic is 2n-2=40, and trisomic is 2n+1=43.

Option A (If both Assertion and Reason are true and Reason is the correct explanation of Assertion) is correct because linked genes on the same chromosome result in a deviation from the expected Mendelian ratio due to a higher proportion of parental gene combinations.

Option D ($50:50$) is correct because a heterozygous yellow seeded plant (Yy) crossed with a green seeded plant (yy) will produce a 1:1 ratio of yellow (Yy) and green (yy) offspring.

Option B is correct because the modern concept of a gene defines it as a functional unit of DNA that codes for a specific product.

The correct answer is C ((A) is true but (R) is false) because while the chromosome arrangement in birds is correct, sex determination is genetic, not temperature-dependent.

Option C (Lethal genes) is correct because lethal genes, when homozygous, cause the death of the organism, resulting in non-viable progeny.

Option B ($3\mathrm{ }:\mathrm{ }1$) is correct because in the F2 generation of a dihybrid cross between YYRR and yyrr, the ratio of yellow to green seed color is 3:1.

Option B (Genes j and K) is correct because crossing over involves the exchange of genetic material between homologous chromosomes, resulting in new combinations of alleles.

Option B (8) is correct because the number of different types of gametes is calculated using the formula 2^n, where n is the number of heterozygous gene pairs.

Option A (Protein structure) is correct because a mutation in a gene ultimately alters the protein structure, leading to a change in the organism's character.

Option B (Homologous chromosome) is correct because crossing over occurs between non-sister chromatids of homologous chromosomes during meiosis.

Option C (Husband of B group and wife of O group) is correct because a child with blood group A cannot have parents with blood groups B and O.

Option D (Higher number of the parental types) is correct because genes located very close together on a chromosome tend to be inherited together, resulting in a higher proportion of parental phenotypes.

Option A (Four) is correct because the number of different gametes is determined by the number of heterozygous gene pairs, which is 2 in this case (Aa and Cc), so $2^2 = 4$.

Option D (heterosis) is correct because heterosis describes the superior performance of F1 hybrids compared to their parents.

Option A (Sex-linked inheritance) is correct because hemophilia is caused by a recessive gene located on the X chromosome.

Option A is correct because the number of gametes is determined by the number of heterozygous loci (2^n), which is 2² = 4 in this case.

Option C (aneuploidy) is correct because aneuploidy is the condition of having an abnormal number of chromosomes, not an exact multiple of the haploid set.

Option B (Crossing over) is correct because X-rays are known to increase the frequency of crossing over during meiosis.

Option B (Mendel) is correct because Gregor Mendel is widely recognized as the father of genetics due to his groundbreaking work on inheritance.

The correct answer is D (Alternative forms of a gene at a given locus) because the production of offspring with 50% dominant and 50% recessive traits suggests a cross between a heterozygous (Aa) and a homozygous recessive (aa) individual, illustrating alternative forms of a gene (alleles) at a specific location (locus).

Option D (Round seeds with yellow cotyledons and wrinkled seeds with yellow cotyledons) is correct because the F1 generation will be RrYy (round, yellow). Selfing the F1 will produce round yellow, round green, wrinkled yellow, and wrinkled green phenotypes. The question asks what phenotypes are expected, not the ratio.