NEET Biology Principles of Inheritance and Variation MCQs Set 21

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Multiple Choice Questions

Question 1: Two linked genes a and b show 20% recombination. The individuals of a dihybrid cross between ++ /++ × ab/ab shall show gametes
(a) + +80 : ab 20
(b) + + 50 : ab 50
(c) + + 40 : ab 40 : + a 10 : + b : 10
(d) + + 30 : ab 30 : + a 20 : + b : 20
Show Answer & Explanation

Answer: (c) + + 40 : ab 40 : + a 10 : + b : 10

Explanation:
1. The F1 is ++/ab with the genes in coupling. Parental gametes ++ and ab are 40% each, and recombinant gametes +a and +b are 10% each.

Teacher's Note:
1. 20% recombination is divided between the two recombinant types.
2. Parentals are more frequent.

Question 2: A normal green male maize is crossed with albino female. The progeny is albino because
(a) trait for albinism is dominant
(b) the albinos have biochemical to destroy plastids derived from green male
(c) plastids are inherited from female parent
(d) green plastids of male must have mutated
Show Answer & Explanation

Answer: (c) plastids are inherited from female parent

Explanation:
1. Plastids are inherited through the egg (maternal), so the albino female gives albino progeny.

Teacher's Note:
1. This is cytoplasmic (plastid) inheritance.
2. Plastid inheritance is maternal.

Question 3: Multiple alleles control inheritance of
(a) phenylketonuria
(b) colourblindness
(c) sickle cell anaemia
(d) blood groups
Show Answer & Explanation

Answer: (d) blood groups

Explanation:
1. Blood groups are controlled by three alleles (IA, IB, i) of one gene, which are multiple alleles.

Teacher's Note:
1. Phenylketonuria, colourblindness and sickle-cell anaemia involve two alleles.
2. ABO is the standard example.

Question 4: Blue eye colour is recessive to brown eye colour. A brown eyed man whose mother was blue eyed marries a blue eyed women. The children shall be
(a) both blue eyed and brown eyed 1 : 1
(b) all brown eyed
(c) all blue eyed
(d) blue eyed and brown eyed 3 :1
Show Answer & Explanation

Answer: (a) both blue eyed and brown eyed 1 : 1

Explanation:
1. The brown-eyed man has a blue-eyed mother, so he is heterozygous (Bb). Crossing with a blue-eyed woman (bb) gives 1 brown : 1 blue.

Teacher's Note:
1. This is a test cross.
2. Find the hidden allele from the mother.

Question 5: A dihybrid condition is
(a) ttRr
(b) Tt rr
(c) tt rr
(d) Tt Rr
Show Answer & Explanation

Answer: (d) Tt Rr

Explanation:
1. A dihybrid is heterozygous for two genes, as in Tt Rr.

Teacher's Note:
1. A monohybrid is heterozygous for one gene.
2. Count the heterozygous gene pairs.

Question 6: Mendel’s last law is
(a) segregation
(b) dominance
(c) independent assortment
(d) polygenic inheritance
Show Answer & Explanation

Answer: (c) independent assortment

Explanation:
1. Mendel's last law is the law of independent assortment, which concerns two or more genes.

Teacher's Note:
1. The first law is dominance and the second is segregation.
2. Laws are numbered in order.

Question 7: First geneticist/father of genetics was
(a) de Vries
(b) Mendel
(c) Darwin
(d) Morgan
Show Answer & Explanation

Answer: (b) Mendel

Explanation:
1. Gregor Mendel is called the father of genetics for his work on pea plants.

Teacher's Note:
1. De Vries, Correns and Tschermak rediscovered his work.
2. Mendel started genetics.

Question 8: The contrasting pairs of factors in Mendelian crosses are called
(a) multiple alleles
(b) allelomorphs
(c) alloloci
(d) paramorphs
Show Answer & Explanation

Answer: (b) allelomorphs

Explanation:
1. The contrasting pairs of factors (alternative forms of a gene) are called allelomorphs or alleles.

Teacher's Note:
1. They occupy the same locus.
2. Allelomorph means other form.

Question 9: RR (red) Antirrhinum is crossed with WW (white) one. Offspring RW are pink. This is an example of
(a) dominant-recessive
(b) incomplete dominance
(c) hybrid
(d) supplementary genes
Show Answer & Explanation

Answer: (b) incomplete dominance

Explanation:
1. When the heterozygote (RW) shows an intermediate phenotype (pink), it is incomplete dominance.

Teacher's Note:
1. The F2 ratio is 1 red : 2 pink : 1 white.
2. Intermediate F1 means incomplete dominance.

Question 10: A gene pair hides the effect of another. The phenomenon is
(a) epistasis
(b) dominance
(c) mutation
(d) None of these
Show Answer & Explanation

Answer: (a) epistasis

Explanation:
1. When one gene masks the effect of another non-allelic gene, it is called epistasis.

Teacher's Note:
1. Dominance is between alleles.
2. Epistasis means standing upon.

Question 11: An allele is dominant if it is expressed in
(a) both homozygous and heterozygous states
(b) second generation
(c) heterozygous combination
(d) homozygous combination
Show Answer & Explanation

Answer: (a) both homozygous and heterozygous states

Explanation:
1. A dominant allele expresses itself in the homozygous as well as the heterozygous condition.

Teacher's Note:
1. A recessive allele shows only in homozygotes.
2. Dominant shows in both states.

Question 12: In a cross between AABB × aabb, the ratio of F2 genotypes between AABB, AaBB, Aabb and aabb would be
(a) 9 : 3 : 3 : 1
(b) 2 : 1 : 1 : 2
(c) 1 : 2 : 2 : 1
(d) 7 : 5 : 3 : 1
Show Answer & Explanation

Answer: (c) 1 : 2 : 2 : 1

Explanation:
1. In the F2 of AABB × aabb, AABB is 1/16, AaBB is 2/16, Aabb is 2/16 and aabb is 1/16. So the ratio is 1 : 2 : 2 : 1.

Teacher's Note:
1. The total is 6 parts out of 16.
2. Count each genotype in the 16 boxes.

Question 13: Segregation of Mendelian factors (no linkage, no crossing over) occurs during
(a) anaphase-I
(b) anaphase-II
(c) diplotene
(d) metaphase-I
Show Answer & Explanation

Answer: (a) anaphase-I

Explanation:
1. Segregation of alleles occurs in anaphase I, when the homologous chromosomes separate.

Teacher's Note:
1. Sister chromatids separate in anaphase II.
2. Homologues separate in anaphase I.

Question 14: An organism with two identical alleles is
(a) dominant
(b) hybrid
(c) heterozygous
(d) homozygous
Show Answer & Explanation

Answer: (d) homozygous

Explanation:
1. An organism with two identical alleles is homozygous.

Teacher's Note:
1. Heterozygous means different alleles.
2. Homo means same.

Question 15: When a certain character is inherited only through female parent, it probably represents
(a) multiple plastid inheritance
(b) cytoplasmic inheritance
(c) incomplete dominance
(d) Mendelian nuclear inheritance
Show Answer & Explanation

Answer: (b) cytoplasmic inheritance

Explanation:
1. A character inherited only from the female parent shows cytoplasmic inheritance, since the egg supplies the cytoplasm.

Teacher's Note:
1. Mitochondria and plastids are inherited this way.
2. Maternal inheritance means cytoplasmic.

Question 16: A polygenic inheritance in human beings is
(a) skin colour
(b) phenylketonuria
(c) colourblindness
(d) sickle cell anaemia
Show Answer & Explanation

Answer: (a) skin colour

Explanation:
1. Human skin colour is controlled by several genes (polygenic).

Teacher's Note:
1. Phenylketonuria, colourblindness and sickle-cell anaemia involve single genes.
2. Skin colour is polygenic.

Question 17: Two dominant non-allelic genes are 50 map units apart. The linkage is
(a) cis type
(b) trans type
(c) complete
(d) absent/incomplete
Show Answer & Explanation

Answer: (d) absent/incomplete

Explanation:
1. Two genes 50 map units apart show 50% recombination, which behaves like independent assortment. So linkage is absent.

Teacher's Note:
1. The maximum recombination value is 50%.
2. Fifty map units means no linkage.

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