NEET Biology Principles of Inheritance and Variation MCQs Set 25

Answer: (a) Garden pea

Explanation:
1. Mendel worked on the garden pea, Pisum sativum (2n = 14), between 1856 and 1863.

Teacher's Note:
1. Garden pea is easy to grow, has a short life cycle and many contrasting traits.
2. It undergoes natural self-pollination and allows artificial cross-pollination.

Answer: (d) 1 : 1

Explanation:
1. The F₂ genotypic ratio is 1 TT : 2 Tt : 1 tt.
2. Homozygous dominant (TT) and homozygous recessive (tt) are therefore in the ratio 1 : 1.

Teacher's Note:
1. Do not confuse the genotypic ratio 1 : 2 : 1 with the phenotypic ratio 3 : 1.
2. Both homozygous classes are always equal in number in a monohybrid F₂.

Answer: (c) 4

Explanation:
1. Tall is dominant over short, so in F₂ tall : short = 3 : 1.
2. Short plants = 1/4 of 16 = 4 (pod colour does not change this count).

Teacher's Note:
1. Treat each character separately and multiply the probabilities.
2. Short plants include both green-podded and yellow-podded ones (3 + 1 of the 4).

Answer: (a) De Vries, Tschermak, Correns

Explanation:
1. Mendel's laws were rediscovered independently in 1900 by Hugo de Vries, Carl Correns and Erich von Tschermak.

Teacher's Note:
1. Correns was from Germany, de Vries from Holland and Tschermak from Austria.
2. Morgan, Bateson and Punnett worked later on chromosomes, linkage and the checkerboard.

Answer: (c) Four

Explanation:
1. In the F₂, the TtRr genotype has a frequency of 1/2 × 1/2 = 1/4.
2. Out of 16 plants that is 4.

Teacher's Note:
1. The genotypes TtRr (4) are the largest genotypic class of the F₂.
2. Check by finding the number of TtRr boxes in the 16-box checkerboard.

Answer: (c) Heterozygous

Explanation:
1. Two different alleles for a character make the individual heterozygous.

Teacher's Note:
1. Dioecious and monoecious describe the distribution of sexes in plants.
2. Heterozygous individuals are also called hybrids.

Answer: (a) 50%

Explanation:
1. Tt × tt gives 1 Tt : 1 tt, so half of the progeny, 50%, are dwarf.

Teacher's Note:
1. This is a test cross.
2. The cross gives tall and dwarf in the ratio 1 : 1.

Answer: (b) Genotype

Explanation:
1. The genotype is the genetic make-up of an organism for a trait.

Teacher's Note:
1. Phenotype is the visible expression.
2. Karyotype describes the chromosome complement.

Answer: (d) Gametes

Explanation:
1. Gametes are haploid, so they carry only one allele of each gene.

Teacher's Note:
1. Zygote, embryo and somatic cells are diploid and have paired alleles.
2. This is the basis of the law of segregation.

Answer: (b) Inheritance

Explanation:
1. Offspring resemble their parents because characters are passed on from parents to progeny by inheritance.

Teacher's Note:
1. Inheritance is the process by which characters pass from parents to offspring.
2. The degree of resemblance depends on the genes inherited.

Answer: (a) One

Explanation:
1. The organism is homozygous for all three gene pairs, so only ABC gametes form: one type.

Teacher's Note:
1. Gamete types = 2ⁿ where n = number of heterozygous pairs.
2. Here n = 0, so only 2⁰ = 1 type.

Answer: (d) Green pod colour

Explanation:
1. Of Mendel's pairs, green pod is dominant over yellow.
2. Terminal flowers, green seeds and wrinkled seeds are recessive traits.

Teacher's Note:
1. Dominant traits: tall, axial, inflated, green pod, round, yellow seed, violet flower.
2. Recessive traits are the opposite member of each pair.

Answer: (a) 50%

Explanation:
1. TT × tt gives all Tt (tall), while Rr × rr gives 1/2 Rr (red) and 1/2 rr.
2. Tall and red = 1 × 1/2 = 50%.

Teacher's Note:
1. Work out each gene pair separately.
2. Multiply the independent probabilities.

Answer: (c) It is expressed in both homozygous and heterozygous conditions

Explanation:
1. A dominant allele shows its effect in the homozygote as well as in the heterozygote.

Teacher's Note:
1. A recessive allele shows its effect only in the homozygous condition.
2. Dominance is the property of an allele, not of the gene as a whole.

Answer: (b) Green seed colour

Explanation:
1. Green seed colour is recessive to yellow seed colour.
2. The other three traits are the dominant members of their pairs.

Teacher's Note:
1. Mendel studied seven pairs of contrasting traits.
2. Learn the dominant and recessive trait of each pair in a table.

Answer: (d) 50%

Explanation:
1. Tt × tt gives Tt and tt in equal numbers.
2. Dwarf plants are therefore 50%.

Teacher's Note:
1. This is again a test cross.
2. The tall : dwarf ratio is 1 : 1.

Answer: (a) All heterozygous tall

Explanation:
1. TT × tt gives only Tt.
2. All the offspring are heterozygous and tall.

Teacher's Note:
1. Tall is dominant over dwarf.
2. The F₁ of two pure parents is uniform.

Answer: (c) Dihybrid cross

Explanation:
1. Independent assortment concerns two gene pairs, which is studied in a dihybrid cross (9 : 3 : 3 : 1).

Teacher's Note:
1. Monohybrid crosses prove dominance and segregation.
2. The 9 : 3 : 3 : 1 ratio shows that the two pairs assort independently.

Answer: (a) 1 : 2 : 2 : 4

Explanation:
1. In the 16-box checkerboard RRYY = 1, RRYy = 2, RrYY = 2 and RrYy = 4.

Teacher's Note:
1. The probability of a genotype is the product of the probabilities for each gene pair.
2. Rr gives 1/4 RR, 1/2 Rr; Yy gives 1/4 YY, 1/2 Yy.

Answer: (d) 8

Explanation:
1. The gametes are 2ⁿ = 2³ = 8 in type.

Teacher's Note:
1. The eight types are ABC, ABc, AbC, Abc, aBC, aBc, abC and abc.
2. The F₂ checkerboard of a trihybrid cross has 64 boxes.

Answer: (b) Back cross

Explanation:
1. A cross of F₁ with either parent is a back cross.
2. It is called a test cross only when the recessive parent is used.

Teacher's Note:
1. All test crosses are back crosses, but not all back crosses are test crosses.
2. Use of the dominant parent gives only dominant phenotypes.

Answer: (a) 9

Explanation:
1. Each gene pair gives 3 genotypes (e.g. TT, Tt, tt), so 3 × 3 = 9 genotypes occur in the F₂.

Teacher's Note:
1. There are 4 phenotypes but 9 genotypes.
2. The 16 boxes of the checkerboard carry these nine genotypes.