NEET Biology Principles of Inheritance and Variation MCQs Set 23

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Chapter-wise Objective Questions: Principles of Inheritance and Variation

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Multiple Choice Questions

Question 1: Both husband and wife have normal vision though their fathers were colourblind. The probability of their daughter becoming colourblind is
(a) 0%
(b) 25%
(c) 50%
(d) 75%
Show Answer & Explanation

Answer: (a) 0%

Explanation:
1. A husband with normal vision has the normal \( X \) (XC \( Y \)), and he passes XC to all his daughters. So no daughter can be colourblind, whatever the wife's genotype.

Teacher's Note:
1. The wife is a carrier.
2. A colourblind daughter needs Xc from both parents.

Question 2: This was elucidated by Francois Jacob and Jacque Monod
(a) 2 and 4
(b) 1 and 4
(c) 2 and 3
(d) 3 and 4
Show Answer & Explanation

Answer: (d) 3 and 4

Explanation:
1. Haemophilia is a recessive X-linked trait. Males have only one \( X \) chromosome, so a single recessive allele shows the disease.

Teacher's Note:
1. Females need two recessive alleles.
2. Hemizygous males show X-linked traits more often.

Question 3: Which one is a hereditary disease?
(a) Cataract
(b) Leprosy
(c) Blindness
(d) Phenylketonuria
Show Answer & Explanation

Answer: (d) Phenylketonuria

Explanation:
1. Phenylketonuria is a hereditary (inborn error of metabolism) disease, caused by a defective gene.

Teacher's Note:
1. Leprosy is an infection, and cataract and blindness are not always hereditary.
2. Genes cause hereditary diseases.

Question 4: A colourblind girl is rare because she will be born only when
(a) her mother and maternal grandfather were colourblind
(b) her father and maternal grandfather were colourblind
(c) her mother is colourblind and father has normal vision
(d) parents have normal vision but grand parents were colourblind
Show Answer & Explanation

Answer: (b) her father and maternal grandfather were colourblind

Explanation:
1. A colourblind girl needs two Xc chromosomes: Xc from her colourblind father and Xc from her mother. The mother can be a carrier if her father (maternal grandfather) was colourblind.

Teacher's Note:
1. Carrier mothers have affected fathers.
2. Trace each \( X \) chromosome back.

Question 5: Down’s syndrome is due to
(a) crossing over
(b) linkage
(c) sex-linked inheritance
(d) non-disjunction of chromosomes
Show Answer & Explanation

Answer: (d) non-disjunction of chromosomes

Explanation:
1. Down's syndrome is due to non-disjunction of chromosome 21 during gamete formation, which gives trisomy 21.

Teacher's Note:
1. It is an aneuploidy.
2. Non-disjunction gives extra chromosomes.

Question 6: A colourblind mother and normal father would have
(a) colourblind sons and normal/carrier daughters
(b) colourblind sons and daughters
(c) all colourblind
(d) all normal
Show Answer & Explanation

Answer: (a) colourblind sons and normal/carrier daughters

Explanation:
1. A colourblind mother (XcXc) and a normal father (XCY) give colourblind sons (XcY) and carrier daughters (XCXc).

Teacher's Note:
1. Sons get the \( X \) of the mother.
2. The criss-cross inheritance of X-linked traits.

Question 7: In human beings 45 chromosomes/single X/XO abnormality causes
(a) Down’s syndrome
(b) Klinefelter’s syndrome
(c) Turner’s syndrome
(d) Edward’s syndrome
Show Answer & Explanation

Answer: (c) Turner’s syndrome

Explanation:
1. A person with a single \( X \) chromosome (45, XO) suffers from Turner's syndrome.

Teacher's Note:
1. Klinefelter's syndrome is XXY and Down's is trisomy 21.
2. XO means Turner.

Question 8: Of a normal couple, half the sons are haemophilic while half the daughters are carriers. The gene is located on
(a) X-chromosome of father
(b) Y-chromosome of father
(c) one X-chromosome of mother
(d) both the X-chromosomes of mother
Show Answer & Explanation

Answer: (c) one X-chromosome of mother

Explanation:
1. Half the sons are haemophilic and half the daughters carriers when the mother is a carrier (one \( X \) has the allele) and the father is normal.

Teacher's Note:
1. Both sons and daughters get one \( X \) from the mother.
2. A carrier mother passes the allele to half her children.

Question 9: Sex is determined in human beings
(a) by ovum
(b) at the time of fertilization
(c) 40 days after fertilization
(d) seventh to eight week when genitals differentiate in foetus
Show Answer & Explanation

Answer: (b) at the time of fertilization

Explanation:
1. Sex is determined at the time of fertilisation, by the type of sperm (\( X \) or \( Y \)) that fertilises the egg.

Teacher's Note:
1. The egg always carries \( X \).
2. The sperm decides the sex.

Question 10: Mr. Kapoor has Bb autosomal gene pair and d allele sex-linked. What shall be proportion of Bd in sperms?
(a) 0
(b) 1/2
(c) 1/4
(d) 1/8
Show Answer & Explanation

Answer: (c) 1/4

Explanation:
1. The man is Bb and \( X^d Y \). The probability of a sperm with \( B \) is 1/2 and with \( X^d \) is 1/2, so Bd is 1/4.

Teacher's Note:
1. Multiply independent probabilities.
2. Gametes combine independent genes.

Question 11: Genes located on Y-chromosome are
(a) mutant genes
(b) sex-linked genes
(c) autosomal genes
(d) holandric genes
Show Answer & Explanation

Answer: (d) holandric genes

Explanation:
1. Genes located on the \( Y \) chromosome are called holandric genes and are passed from father to son.

Teacher's Note:
1. X-linked genes are sex-linked.
2. Holandric means only in males.

Question 12: A colourblind woman marries a normal visioned male. In the offspring
(a) both son and daughter are colourblind
(b) all daughters are colourblind
(c) all sons are normal
(d) all sons are colourblind
Show Answer & Explanation

Answer: (d) all sons are colourblind

Explanation:
1. A colourblind woman (XcXc) and a normal man (XCY) give all colourblind sons and all carrier daughters.

Teacher's Note:
1. Sons get Xc from the mother.
2. All sons are affected.

Question 13: An individual exhibiting both male and female sexual characteristics in the body is known as
(a) hermaphrodite
(b) intersex
(c) gynandromorph
(d) bisexual
Show Answer & Explanation

Answer: (c) gynandromorph

Explanation:
1. An individual showing both male and female characters in different body parts is a gynandromorph.

Teacher's Note:
1. It is common in insects.
2. Gynandromorph means mosaic of sexes.

Question 14: Genetic identity of a human male is determined by
(a) autosome
(b) nucleolus
(c) sex chromosome
(d) cell organelles
Show Answer & Explanation

Answer: (c) sex chromosome

Explanation:
1. The genetic identity (sex) of a human male is determined by the sex chromosomes (XY).

Teacher's Note:
1. Autosomes do not decide sex.
2. Sex chromosomes decide sex.

Question 15: Foetal sex can be determined by examining cells from the amniotic fluid by looking for
(a) Barr bodies
(b) autosomes
(c) chiasmata
(d) kinetochore
Show Answer & Explanation

Answer: (a) Barr bodies

Explanation:
1. Barr bodies (inactive \( X \)) can be seen in cells from the amniotic fluid, which helps to identify the sex of the foetus.

Teacher's Note:
1. A female cell has one Barr body.
2. Barr body means female.

Question 16: Loss of an X-chromosome in a particular cell, during its development, results into
(a) diploid individual
(b) triploid individual
(c) gynandromorphs
(d) both
Show Answer & Explanation

Answer: (c) gynandromorphs

Explanation:
1. Loss of an \( X \) chromosome in a cell during development gives patches of male (XO) and female (XX) tissue, forming a gynandromorph.

Teacher's Note:
1. It is seen in Drosophila.
2. Chromosome loss gives mosaics.

Question 17: Mental retardation in man, associated with sex chromosomal abnormality is usually due to
(a) reduction in X-complement
(b) increase in X-complement
(c) moderate increase in Y-complement
(d) large increase in Y-complement
Show Answer & Explanation

Answer: (b) increase in X-complement

Explanation:
1. Mental retardation in sex chromosome abnormalities is usually due to an increase in the number of \( X \) chromosomes, as in XXY.

Teacher's Note:
1. Turner's XO has normal intelligence.
2. Extra \( X \) means retardation.

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Practice MCQs for NEET Biology Principles of Inheritance and Variation

NEET Biology Principles of Inheritance and Variation Objective Test Questions

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