Hereditary and Variation MCQs for NEET — Botany Questions with Answers

The term linkage was coined by TH Morgan. He carried out several dihybrid crosses in Drosophila to study genes that were sex-linked. He described the physical association of genes on a chromosome.

(b) The movement of a gene from one linkage group to another is called translocation. It is a chromosome abnormality caused by rearrangement of parts between nonhomologous chromosomes.

(c) Mutiple alleles is a condition where a gene exist in more than two allelic forms that are present on the same locus of the chromosome. For eg : ABO system in humans.

The law of dominance does not occur universally. After Mendel several cases were recorded by scientists, where a clear deviation from law of dominance was seen in the form of incomplete dominance or Blending inheritance and Co-dominance. 

Where F₁ generation hybrids exhibited a mixture or blending of character of two parents, the case is considered as that of incomplete dominance blending inheritance. It is simply means that two genes of allelomorphic pair are not related as dominant or recessive, but each of them expresses itself partially. In the case of 4 o'clock plant, when plants with red flowers are crossed with plants having white flower, the F₁ hybrids bear pink flowe. When these pink flowers are self pollinated, they develop red, pink and white flowers in the ratio of 1 : 2 : 1 respectively. 

In genetics, a test cross, first introduced by Gregor Mendel, is used to determine if an individual exhibiting a dominant trait is homozygous or heterozygous for that trait. More simply, test cross determines the genotype of an individual with a dominant phenotype. In some sources, the test cross is defined as being a type of back cross between the recessive homozygote and F₁ generation.

In ABO blood groups system, inheritance of grouping is controlled by a single autosomal gene on chromosome 9 with three major alleles A, B and O ( I^A, I^B and i^O). The ABO blood group system has at least 6 genotypes. on the basis of presence or absence of antigens and antibodies, four blood groups (phenotypes) have been differentiated — A, B, AB and O blood groups. 

Recombination is a rearrangement of genes during meiosis so that a gamete contains a haploid genotype with a new gene combination. Morgan and his group found that when genes were grouped on the same chromosome, some genes were very tightly linked (showed very low recombination), while others were loosely linked (showed higher recombination).

Inheritance of skin colour in humans is the result of polygenic inheritance or multiple factor inheritance. The inheritance of human skin colour was studied by C.B. Davenport in 1913.

The more maternal influence can be expected in the cytoplasmic inheritance (i.e., the inheritance of genes contained in the cytoplasm of a cell, rather than the nucleus). The resason is that the female reproductive cell or the egg has a large amount of cytoplasm containing many such organelles which ciontain their own genes and can reproduce independently (e.g., mitochondra and chloroplast) and whcih are consequently incorporated into the cytoplasm of all the cells of the embryo. The male reproductive cells (sperm or pollen) consist almost solely of a nucleus. Cytoplasmic organelles are thus, not inherited from the male parent. 

This is why, the cytoplasmic inheritance is also called as maternal inheritance.

Genes located on Y-chromosome are called Y-genes and their inheritance is called Y-linked inheritance. This carries the paternal influences.

A gene located in the X-chromosome is said to be X-linked and its inheritance is called X-linked inheritance. In this, a male transmits his X-chromosome only to his daughters while a female transmits one of her X-chromosomes to the offspring of both sexes. 

The types of gametes produced by a plant depend upon the number of heterozygous pair.

Number of types f gametes = Zⁿ

n = nymber of heterozygous pair

2¹ = 2

The gametes are — ABC and AbC.