Genetics – Inheritance of One Gene (Monohybrid cross): NEET MCQs with Answers

15 free questions on Genetics – Inheritance of One Gene (Monohybrid cross) for NEET (UG), starting with previous-year NEET and AIPMT questions. Try each one, then tap Show answer for the answer and a short explanation.

Syllabus covered: Inheritance of One Gene (Monohybrid cross)

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Question 1

Previous-year question
A tall true-breeding garden pea plant is crossed with a dwarf true-breeding garden pea plant. When the F1 plants were selfed, the resulting genotypes were in the ratio of [NEET 2016]
  1. 1:2:1 :: tall homozygous : tall heterozygous : dwarf
  2. 1:2:1 :: tall heterozygous : tall homozygous : dwarf
  3. 3:1 :: tall : dwarf
  4. 3:1 :: dwarf : tall
Show answer
Answer: (A) 1:2:1 :: tall homozygous : tall heterozygous : dwarf
Explanation: The F1 is Tt, and selfing gives 1 TT : 2 Tt : 1 tt. Hence the genotypic ratio is 1 tall homozygous : 2 tall heterozygous : 1 dwarf, corresponding to the 3:1 phenotypic ratio.

Question 2

Previous-year question
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 [AIPMT 1991]
  1. both blue eyed and brown eyed 1 : 1
  2. all brown eyed
  3. all blue eyed
  4. blue eyed and brown eyed 3 : 1
Show answer
Answer: (A) both blue eyed and brown eyed 1 : 1
Explanation: A brown-eyed man whose mother was blue-eyed must be heterozygous, Bb. Bb × bb is a test cross, so half the children are Bb (brown eyed) and half bb (blue eyed), giving a 1 : 1 ratio.

Question 3

Previous-year question
An organism with two identical alleles is [AIPMT 1992]
  1. dominant
  2. hybrid
  3. heterozygous
  4. homozygous
Show answer
Answer: (D) homozygous
Explanation: An organism carrying two identical alleles of a gene, e.g. TT, tt or RR, is homozygous (pure) for that character. If the two alleles are different, e.g. Tt, the organism is heterozygous or hybrid.

Question 4

Previous-year question
Hybridisation between Tt × tt gives rise to the progeny of ratio [AIPMT 1999]
  1. 1 : 1
  2. 1 : 2 : 1
  3. 1 : 2
  4. 4 : 1
Show answer
Answer: (A) 1 : 1
Explanation: Tt produces T and t gametes in equal numbers whereas tt produces only t. The progeny are therefore Tt and tt in equal numbers, giving a 1 : 1 ratio of tall to dwarf.

Question 5

Previous-year question
A gene is said to be dominant if [AIPMT 2002]
  1. it expresses its effect only in homozygous state
  2. it expresses its effect only in heterozygous condition
  3. it expresses its effect both in homozygous and heterozygous condition
  4. it never expresses its effect in any condition
Show answer
Answer: (C) it expresses its effect both in homozygous and heterozygous condition
Explanation: A dominant factor is an allele that expresses itself both in the heterozygous and in the homozygous condition, thereby masking the recessive allele. By convention it is denoted by a capital letter.

Question 6

Previous-year question
Two crosses between the same pair of genotypes or phenotypes in which the sources of the gametes are reversed in one cross, is known as [AIPMT 2003]
  1. dihybrid cross
  2. reverse cross
  3. test cross
  4. reciprocal cross
Show answer
Answer: (D) reciprocal cross
Explanation: When the same two genotypes are crossed twice with the sexes of the parents interchanged, the pair of crosses is called a reciprocal cross. It is used to test whether the inheritance of a character depends on the sex of the parent contributing it.

Question 7

Previous-year question
Test cross involves [AIPMT 2006]
  1. crossing between two genotypes with recessive trait
  2. crossing between two F₁-hybrids
  3. crossing the F₁-hybrid with a double recessive genotype
  4. crossing between two genotypes with dominant trait
Show answer
Answer: (C) crossing the F₁-hybrid with a double recessive genotype
Explanation: A test cross is the crossing of an F₁-hybrid with a homozygous double recessive parent. It reveals the heterozygosity or homozygosity of the tested individual; in a dihybrid test cross the resulting ratio is 1 : 1 : 1 : 1.
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Question 8

Previous-year question
A common test to find the genotype of a hybrid is by [AIPMT 2007]
  1. crossing of one F₂-progeny with male parent
  2. crossing of one F₂-progeny with female parent
  3. studying the sexual behaviour of F₁-progenies
  4. crossing of one F₁-progeny with male parent
Show answer
Answer: (D) crossing of one F₁-progeny with male parent
Explanation: The genotype of a hybrid is determined by a test cross, that is by crossing an F₁-progeny back to the homozygous recessive parent. The proportions of dominant and recessive offspring then reveal whether the hybrid was homozygous or heterozygous.

Question 9

Previous-year question
In pea plants, yellow seeds are dominant to green. If a heterozygous yellow seeded plant is crossed with a green seeded plant, what ratio of yellow and green seeded plants would you expect in F₁-generation? [AIPMT 2007]
  1. 50 : 50
  2. 9 : 1
  3. 1 : 3
  4. 3 : 1
Show answer
Answer: (A) 50 : 50
Explanation: Yy × yy is a test cross. The heterozygote produces Y and y gametes in equal proportion while the green parent produces only y, so the offspring are Yy and yy in equal numbers, giving 50% yellow and 50% green.

Question 10

Previous-year question
The genotype of a plant showing the dominant phenotype can be determined by [AIPMT 2010]
  1. test cross
  2. dihybrid cross
  3. pedigree analysis
  4. back cross
Show answer
Answer: (A) test cross
Explanation: A test cross — crossing the individual with a homozygous recessive — is the standard method to determine whether an organism showing a dominant phenotype is homozygous or heterozygous for that trait.

Question 11

Previous-year question
Which one of the following cannot be explained on the basis of Mendel's Law of Dominance? [AIPMT 2010]
  1. The discrete unit controlling a particular character is called a factor
  2. Out of one pair of factors one is dominant, and the other recessive
  3. Alleles do not show any blending and both the characters recover as such in F₂-generation
  4. Factors occur in pairs
Show answer
Answer: (C) Alleles do not show any blending and both the characters recover as such in F₂-generation
Explanation: Mendel's law of dominance does not apply universally. Cases such as incomplete dominance and codominance, in which the alleles blend or both express themselves, cannot be explained by the law of dominance; the recovery of both characters as such in F₂ is explained by the law of segregation.

Question 12

Previous-year question
Test cross in plants or in Drosophila involves crossing [AIPMT 2012]
  1. between two genotypes with recessive trait
  2. between two F₁-hybrids
  3. the F₁-hybrid with a double recessive genotype
  4. between two genotypes with dominant
Show answer
Answer: (C) the F₁-hybrid with a double recessive genotype
Explanation: A test cross involves crossing the F₁-hybrid with the double recessive parent. If the unknown genotype is heterozygous the recessive trait appears in half of the offspring, whereas if it is homozygous dominant all the offspring show the dominant trait.

Question 13

Previous-year question
A test cross is carried out to [AIPMT 2012]
  1. determine the genotype of a plant at F₂
  2. predict whether two traits are linked
  3. assess the number of alleles of a gene
  4. determine whether two species or varieties will breed successfully
Show answer
Answer: (A) determine the genotype of a plant at F₂
Explanation: A test cross is used to determine the genotype of an F₂ individual showing the dominant phenotype. The unknown is crossed with a homozygous recessive parent; a uniformly dominant progeny indicates homozygosity, whereas a 1 : 1 ratio indicates heterozygosity.

Question 14

Previous-year question
A tall true breeding garden pea plant is crossed with a dwarf true breeding garden pea plant. When the F₁ plants were selfed, the resulting genotypes were in the ratio of [NEET 2016, Phase II]
  1. 1 : 2 : 1 :: Tall heterozygous : Tall homozygous : Dwarf
  2. 3 : 1 :: Tall : Dwarf
  3. 3 : 1 :: Dwarf : Tall
  4. 1 : 2 : 1 :: Tall homozygous : Tall heterozygous : Dwarf
Show answer
Answer: (D) 1 : 2 : 1 :: Tall homozygous : Tall heterozygous : Dwarf
Explanation: TT × tt gives all Tt (tall) in F₁. On selfing, the F₂ shows the genotypes TT : Tt : tt in the ratio 1 : 2 : 1, i.e. 1 tall homozygous : 2 tall heterozygous : 1 dwarf, while the phenotypic ratio is 3 tall : 1 dwarf.

Question 15

Previous-year question
Select the correct statement. [NEET 2018]
  1. Spliceosomes take part in translation
  2. Punnett square was developed by a British scientist
  3. Franklin Stahl coined the term 'linkage'
  4. Transduction was discovered by S. Altman
Show answer
Answer: (B) Punnett square was developed by a British scientist
Explanation: The Punnett square was developed by the British geneticist Reginald C. Punnett. Spliceosomes act in splicing of the primary transcript, not in translation, the term linkage was coined by T. H. Morgan, and transduction was discovered by Zinder and Lederberg.

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