Principle of inheritance and variation practice · Mixed difficulty

Option D (Both tall and dwarf plants in 3 : 1 ratio) is correct because in the F2 generation of a monohybrid cross (TT x tt), the phenotypic ratio of tall to dwarf plants is 3:1.

Option D (Both A and B are false) is correct because Turner syndrome is due to sex chromosome monosomy, and high temperature can be a physical mutagen.

Option A (Sex-chromosome) is correct because the sex chromosomes (X and Y) determine the genetic sex and identity of a human male.

Option D (Tt and tt only) is correct because the ratio of tall to dwarf plants (approximately 3:1) suggests a cross between heterozygous (Tt) and homozygous recessive (tt) plants.

Option D is correct because incomplete dominance, codominance, and multiple alleles are all examples of intergenic gene interactions.

Option A (Genes) is correct because Mendel used the term \"factor\" to refer to what we now know as genes, the units of heredity.

Option C (4) is correct because there are four conditions exhibiting dissimilar sex chromosomes: XXY (Klinefelter syndrome), XYY, XXX (Triple X syndrome), and XO (Turner syndrome).

The correct answer is B (Violet) because in Mendel's experiments with pea plants, violet flower color was dominant. Therefore, if 'W' represents the dominant allele for violet and 'ω' represents the recessive allele, Wω will express the dominant violet phenotype.

Option A (Recessive) is correct because most mutations are recessive, meaning they are only expressed when homozygous.

Option A (Mendelian disorder) is correct because Mendelian disorders are inherited according to Mendel's laws of inheritance, involving single genes with dominant or recessive patterns.

Option A (A-extremely, B-carrier, C-haemophilic) is correct because a female can only have hemophilia if her mother is at least a carrier and her father is hemophilic.

Option B ($50 \%$) is correct because the affected mother produces gametes with either an extra chromosome 21 or a normal set, leading to a 50% chance of the offspring inheriting Down's syndrome.

Option C (Intermediate sized round seeds) is correct because the Bb genotype produces an intermediate phenotype due to incomplete dominance, resulting in intermediate-sized round seeds.

Option A (A-A; B-genetic) is correct because night blindness can be corrected by giving vitamin A, but color blindness is a genetic disease and cannot be cured by vitamins.

Option A is correct because harmful dominant mutations can persist if they have a beneficial effect in heterozygotes, preventing their complete elimination.

Option C (Myotonic dystrophy) is correct because Myotonic dystrophy is an autosomal dominant disorder, while the others are recessive or X-linked.

The correct answer is B (50% colourblind) because the woman is a carrier, and the man is normal, resulting in a 50% chance of colorblind sons.

The correct answer is B (2500) because if 16% of the population are ebony fruit flies, and that number is 400, then the total population can be calculated.

Option D is correct because a Punnett square is a graphical representation used to calculate the probability of all possible genotypes of offspring in a genetic cross.

Option D (VWTU) is correct because the gene sequence is determined by minimizing the distances between adjacent genes based on the given crossover values.

Option A (AB antigen) is correct because individuals with blood group AB have both A and B antigens on their red blood cells.

Option A (ZZ-ZW) is correct because birds use the ZZ-ZW system for sex determination, where males are ZZ and females are ZW.

Option A is correct because recessive characters are only expressed in homozygous conditions, making them always pure in expression.

Option D (Both (A) and (R) are false) is correct because X-linked recessive traits show transmission from carrier female to male progeny and exhibit crisscross inheritance.

Option C ($\frac{1}{16}$) is correct because the probability of having a son is 1/2, and for four sons in a row, it's (1/2)⁴.

Option A (8 different gametes and 64 different zygotes) is correct because a trihybrid plant (AaBbCc) forms $2^3 = 8$ different gametes, and the number of zygotes is $8 \times 8 = 64$.

Option D (ZW) is correct because in birds, the female is the heterogametic sex, represented by ZW, while the male is homogametic, represented by ZZ.

Option A (A-homozygous; B-heterozygous) is correct because a homozygous gene produces similar gametes, while a heterozygous gene produces two kinds of gametes with equal proportions.

Option B (Genotype and environment interactions) is correct because the phenotype is the result of the interaction between an organism's genetic makeup (genotype) and its environment.

Option C (Aneuploidy – due to non-disjunction) is correct because Turner syndrome results from aneuploidy (specifically monosomy X) caused by non-disjunction during meiosis.