NEET Biology Principles of Inheritance and Variation MCQs Set 07

Answer: (b) independent assortment

Explanation:
1. In a dihybrid cross, the two gene pairs assort independently into gametes.
2. This gives new combinations of parental characters, called recombinants.

Teacher's Note:
1. Independent assortment gives recombinants for genes on different chromosomes.
2. Crossing over gives recombinants for linked genes.

Answer: (a) He carried out artificial hybridisation (controlled cross-pollination) experiments on garden pea

Explanation:
1. Mendel crossed pea plants by artificial cross-pollination after emasculation.
2. He used a large sampling size, which made his ratios statistically reliable.

Teacher's Note:
1. Somatic hybridisation fuses somatic cells and was not known in Mendel's time.
2. Drosophila was used later by Morgan.

Answer: (b) alteration of DNA sequences

Explanation:
1. A mutation is a change in the DNA sequence (base substitution, insertion, deletion or chromosomal change).
2. It can produce a new allele and so a new phenotype.

Teacher's Note:
1. Mutation is the source of new alleles.
2. Recombination only reshuffles existing alleles.

Answer: (b) Its life cycle takes about four months

Explanation:
1. Drosophila completes its life cycle in about two weeks, not four months.
2. The other three statements are true reasons for its use.

Teacher's Note:
1. Short life cycle, large progeny and clear sex differences are the main advantages.
2. Morgan used it to study sex linkage.

Answer: (a) pleiotropic gene

Explanation:
1. A pleiotropic gene produces a single product that influences several traits.
2. Polygenes are many genes controlling one trait.

Teacher's Note:
1. Do not confuse pleiotropy with polygenic inheritance.
2. Phenylketonuria is a pleiotropic effect of one gene.

Answer: (b) Inheritance of one character is not always independent of the inheritance of other characters, for example in linked genes

Explanation:
1. Genes on the same chromosome are inherited together (linkage).
2. So inheritance of two characters is not always independent.

Teacher's Note:
1. Independent assortment holds for genes on different chromosomes.
2. Linkage is the exception.

Answer: (c) by sexual reproduction with mostly self-pollination

Explanation:
1. Pea flowers are bisexual and normally self-pollinate.
2. Reproduction is sexual, not asexual.

Teacher's Note:
1. Self-pollination gave Mendel pure lines.
2. He used artificial cross-pollination for hybrids.

Answer: (b) Sickle cell anaemia is autosomal recessive, whereas haemophilia is X-linked recessive

Explanation:
1. The sickle cell gene is on an autosome and the disease is recessive.
2. The haemophilia gene is on the X chromosome.

Teacher's Note:
1. Sickle cell anaemia can affect males and females equally.
2. Haemophilia affects males more often.

Answer: (c) alleles do not show any blending and both characters are recovered in the F2

Explanation:
1. Alleles remain separate in the hybrid and separate again at gamete formation.
2. So both parental traits reappear in the F2.

Teacher's Note:
1. The law of segregation is also called the law of purity of gametes.
2. A gamete carries only one allele of each gene.

Answer: (a) Using mathematics to explain biological phenomena was a totally new approach

Explanation:
1. Mendel applied statistical analysis and mathematical logic to hybridisation results.
2. This was new at that time.

Teacher's Note:
1. Mendel could not provide physical proof for the factors.
2. Chromosomal evidence came later.

Answer: (a) diploid cells

Explanation:
1. Diploid cells carry two sets of chromosomes, so genes and chromosomes both exist in pairs.
2. Gametes carry one set.

Teacher's Note:
1. This parallel behaviour led to the chromosomal theory of inheritance.
2. The theory was proposed by Sutton and Boveri.

Answer: (d) gene

Explanation:
1. Alleles are alternative forms of a gene.
2. They occupy the same locus on homologous chromosomes.

Teacher's Note:
1. Different alleles arise by mutation.
2. They can produce different phenotypes.

Answer: (d) haemophilic

Explanation:
1. A haemophilic daughter must receive an affected X from both parents.
2. The father must therefore be haemophilic and the mother at least a carrier.

Teacher's Note:
1. Such a mating is rare, so affected females are very rare.
2. Sons are far more commonly affected.

Answer: (c) Sutton and Boveri

Explanation:
1. Sutton and Boveri noted that chromosomes and genes behave alike in pairing and segregation.
2. This led to the chromosomal theory of inheritance.

Teacher's Note:
1. Sutton united chromosome behaviour with Mendelian principles.
2. Morgan later gave experimental proof.

Answer: (a) Two

Explanation:
1. Half the sperms carry X and half carry Y.
2. So two types of gametes are produced.

Teacher's Note:
1. The male is heterogametic.
2. The sex of the child depends on the sperm.

Answer: (b) linked genes

Explanation:
1. Genes on one chromosome tend to be inherited together, so they are linked.
2. All genes on one chromosome form a linkage group.

Teacher's Note:
1. Linked genes do not assort independently.
2. Crossing over can separate them.

Answer: (b) Dominance

Explanation:
1. In complete dominance the F1 looks like one of the parents.
2. In incomplete dominance it is intermediate and in codominance both parental traits show.

Teacher's Note:
1. Mendel's pea crosses showed complete dominance.
2. Snapdragon shows incomplete dominance.

Answer: (b) linkage group

Explanation:
1. Genes located on one chromosome form a linkage group.
2. The number of linkage groups equals the haploid number.

Teacher's Note:
1. Linked genes are inherited together.
2. Drosophila has four linkage groups.

Answer: (d) son

Explanation:
1. Holandric genes are on the Y chromosome, which a father passes to his sons only.
2. Daughters do not receive a Y.

Teacher's Note:
1. Y-linked traits show strict father to son transmission.
2. They never appear in females.

Answer: (d) chromosomal theory of inheritance

Explanation:
1. Sutton joined the behaviour of chromosomes with Mendel's factors.
2. The result is the chromosomal theory of inheritance.

Teacher's Note:
1. Boveri worked independently on the same idea.
2. Morgan later gave experimental support.

Answer: (b) recessive

Explanation:
1. A mutation usually reduces or destroys the function of a gene product.
2. The modified allele is then recessive.

Teacher's Note:
1. The normal allele usually produces the working enzyme.
2. A recessive trait is seen only when both alleles are modified.

Answer: (c) A-2, B-3, C-1

Explanation:
1. Hypertrichosis of the ear is Y-linked.
2. Colour blindness is X-linked and sickle cell anaemia is autosomal recessive.

Teacher's Note:
1. Y-linked traits are holandric.
2. Sickle cell anaemia is due to one base change in the beta globin gene.

Answer: (c) 1-E, 2-A, 3-B, 4-C, 5-D

Explanation:
1. Sickle cell anaemia gives sickle-shaped RBCs and bleeder's disease is haemophilia.
2. De Vries proposed mutation, O is the universal donor and Mendel worked on Pisum sativum.

Teacher's Note:
1. Bleeder's disease is another name for haemophilia.
2. The O group lacks both A and B antigens.