NEET Biology Principles of Inheritance and Variation MCQs Set 05

Answer: (a) The degree by which progeny differs from their parents

Explanation:
1. Variation is the difference between offspring and their parents (and among siblings).
2. Passing of characters from parent to progeny is inheritance, so (c) is not variation.

Teacher's Note:
1. Inheritance is the similarity; variation is the difference.

Answer: (c) Both dominance and segregation

Explanation:
1. The phenotypic ratio 3:1 arises because one allele is dominant (so 3 show it) and because the alleles segregate (so the recessive reappears in 1).
2. Hence both ideas are needed.

Teacher's Note:
1. The genotypic ratio 1:2:1 reflects segregation alone.

Answer: (b) Incomplete dominance

Explanation:
1. An intermediate F1 phenotype shows that neither allele is completely dominant.
2. This is incomplete dominance, as in flower colour of snapdragon or Mirabilis.

Teacher's Note:
1. Incomplete dominance gives 1:2:1 in both phenotype and genotype in F2.

Answer: (d) All of the above

Explanation:
1. A mutated allele can change the enzyme's structure so it works less well or not at all.
2. It can also stop enzyme production altogether, so all are possible.

Teacher's Note:
1. Recessive traits usually arise from loss of function.

Answer: (a) A normal enzyme

Explanation:
1. If the modified allele makes a normal (equally efficient) enzyme, the phenotype is the same as with the unmodified allele.
2. Non-functional or absent enzymes would change the phenotype.

Teacher's Note:
1. A silent change in DNA may give the same enzyme.

Answer: (c) Both formation of a non-functional enzyme and no enzyme production

Explanation:
1. The recessive allele usually codes for a non-functional enzyme or no enzyme.
2. In the heterozygote the dominant allele still makes enough functional enzyme, so the recessive trait is seen only in homozygotes.

Teacher's Note:
1. A functional enzyme gives the dominant phenotype.

Answer: (a) Population studies are made

Explanation:
1. An individual carries only two alleles of a gene.
2. More than two alleles can be seen only when the population is studied.

Teacher's Note:
1. ABO blood group has three alleles in the population but each person has two.

Answer: (a) When genes are grouped on the same chromosome, some genes are very tightly linked and show very low recombination

Explanation:
1. Tightly linked genes lie close together on a chromosome, so crossing over between them is rare and recombination is very low.
2. Loosely linked genes lie farther apart and show more recombination.

Teacher's Note:
1. Recombination frequency is proportional to the distance between genes.

Answer: (b) 1.3%

Explanation:
1. Yellow body and white eyes are tightly linked on the X chromosome.
2. Morgan observed only 1.3% recombinants, while 98.7% were parental types.

Teacher's Note:
1. Body colour and eye colour (yellow/white) are tightly linked; white eyes and miniature wings were 37.2%.

Answer: (a) XO type

Explanation:
1. In many insects the male has one X chromosome (XO) and the female has XX.
2. XY is the human and Drosophila type, and ZW is found in birds.

Teacher's Note:
1. XO: grasshopper; XY: humans and Drosophila; ZW: birds.

Answer: (d) A square joined to a circle by a double line represents a marriage between relatives

Explanation:
1. In a pedigree, a square is a male, a circle is a female and a diamond is an individual of unspecified sex.
2. A double horizontal line between the partners denotes consanguineous mating (marriage between relatives).

Teacher's Note:
1. Consanguinity is shown by a double line between the partners.

Answer: (c) Father - Aa, Mother - Aa

Explanation:
1. Both parents are unaffected, so neither is aa.
2. They have affected (aa) children, so each must have passed on a recessive allele, hence both are carriers (Aa).

Teacher's Note:
1. Two carriers have a one in four chance of an affected child.

Answer: (c) 37.5%

Explanation:
1. Tt x Tt gives 3/4 tall.
2. Yy x yy gives 1/2 green, so tall and green are 3/4 x 1/2 = 3/8 = 37.5%.

Teacher's Note:
1. Treat each gene separately and multiply the probabilities.

Answer: (d) c and e

Explanation:
1. Drosophila is useful because it grows easily, has a short life cycle and shows many visible variations.
2. A few progeny per mating and difficulty in telling the sexes would make it unsuitable, but in reality a single mating produces many progeny and the sexes are easy to distinguish, so (c) and (e) are the unsuitable features.

Teacher's Note:
1. Drosophila: short life cycle, many progeny per mating, clear sexes.

Answer: (d) Both flower colour in Mirabilis and size of starch grains in pea

Explanation:
1. Mirabilis (4 o'clock plant) shows red, pink and white flowers in 1:2:1, which is incomplete dominance.
2. Starch grain size in pea is also intermediate in the heterozygote; flower colour in pea shows complete dominance.

Teacher's Note:
1. Dog flower (snapdragon) is another example.

Answer: (d) Both statistical analysis and mathematical logic

Explanation:
1. Mendel counted his progeny and analysed the ratios statistically.
2. He also used mathematical logic to derive his principles, which was new in biology.

Teacher's Note:
1. Mendel's large sample sizes strengthened his results.

Answer: (b) Has undergone continuous self pollination

Explanation:
1. Continuous self pollination for several generations makes the line homozygous.
2. It then shows stable trait inheritance for several generations.

Teacher's Note:
1. True breeding means homozygous for the trait.

Answer: (d) Seed colour: green / yellow

Explanation:
1. In Mendel's pea, violet, axial, inflated and yellow are dominant traits.
2. For seed colour yellow is dominant and green recessive, so the given order is reversed.

Teacher's Note:
1. Round, yellow, violet, axial, inflated, green pod and tall are dominant.

Answer: (b) 50%

Explanation:
1. A heterozygote produces two kinds of gametes.
2. Each gamete carries one allele and either allele is equally likely, so the chance is 50%.

Teacher's Note:
1. Gametes are always haploid for that gene.

Answer: (b) Punnett square

Explanation:
1. The Punnett square was developed by Reginald Punnett.
2. It shows all combinations of male and female gametes.

Teacher's Note:
1. Emasculation is removal of anthers.

Answer: (b) 50%

Explanation:
1. A Tt plant makes T and t gametes in equal numbers.
2. Each pollen has a 50% chance of being T, and it is the T gamete that fertilises a T egg, so the chance is 50%.

Teacher's Note:
1. Probabilities of independent events multiply when both are needed.

Answer: (a) F1 and F2

Explanation:
1. In the F1 only the dominant parental character is seen.
2. In the F2 both the dominant and recessive characters appear.

Teacher's Note:
1. Dominance explains F1, segregation explains F2.

Answer: (d) Either a non-functional enzyme or no enzyme

Explanation:
1. The recessive allele either codes for an enzyme that does not work or does not produce the enzyme.
2. So the recessive phenotype appears when both alleles are of this type.

Teacher's Note:
1. Both loss-of-function types cause the recessive phenotype.