Genetics and Plant Breeding

Genes for different traits can segregate independently during the formation of gametes. This is the result of Law of independent assortment which was studied Mendel. Therefore, (C) is the correct answer.

During gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene. This was proposed in the Law of segregation. Therefore, (b) is the correct answer.

Mendel's law of Segregation: The principle of segregation describes how pairs of gene variants are separated into reproductive cells. The segregation of gene variants, called alleles, and their corresponding traits was first observed by Gregor Mendel in 1865. Mendel was studying genetics by performing mating crosses in pea plants.
Each gamete receives one gene for an allele and thus, is haploid in nature. Both male and female gametes, which are haploid will fuse and forms a diploid zygote.

Recessive freq $= q= 0.8$
$q^2 = (0.8)^2 =0.64$  
$p^2 + q^2 = 1$  
$1 - q^2 = p^2$ 
$ p^2 = 1 - 0.64= 0.36$ 
$0.36 \times 1300 = 468$

If dominant phenotype percentage is given, we come to know about the percentage of homozygous recessive in population: which in this case is $25$%. Thus frequency of recessive allele is $0.50$.

So, the correct option is '0.50'.

Using Hardy-Weinberg equilibrium: q^2 = 100/N. Given q = 0.4, then q^2 = 0.16. So, 0.16 = 100/N, which means N = 100 / 0.16 = 625.

Hybridisation is the interbreeding between two genetically different organisms from the same or different species. When such interbreeding is between different species it is known as interspecific hybridisation. Genetically modified crops are those that are genetically engineered by introducing the genes of the desired trait (character) into the plants. When the cross is between two different varieties of the same species then it is known as intervarietal hybridisation. So, the correct options are 'Hybridisation means crossing between genetically dissimilar plants and Introducing genes of the desired character into a plant gives genetically modified crop'.

As established in previous questions, both blood group matching and HLA matching are fundamental requirements for determining the compatibility between a donor and a recipient for a kidney transplant.

Isograft is a tissue or organ transplanted from a donor to a recipient who are identical or monozygotic twins. In an isograft transplantation the chances of rejection are near to nil with identical MHCs as they are genetically identical.

A xenograft involves transplanting tissue between different species, which results in the highest level of genetic variation and the most severe immune rejection response compared to autografts or allografts.

Triticale is a crop species (cereal grain) formed as a result of cross between wheat (Triticum) and rye (Secale). It combines the yield potential and grain quality of wheat with the disease and environmental tolerance (including soil conditions) of rye. So, the correct option is 'wheat and rye'.

Pleiotropy occurs when one gene will code and control the phenotype or expression of several different and unrelated traits. Phenylketonuria is an autosomal recessive disorder controlled by a mutant gene present on the 12th chromosome. This mutant gene fails to code for the enzyme phenylalanine hydroxylase required for normal metabolism of amino acid phenylalanine to tyrosine. Due to this, there is an accumulation of phenylalanine in body fluids such as blood, sweat, CSF. An abnormal breakdown product phenyl ketone is found in urine A higher level of phenylalanine and pheylketone cause severe brain damage leading to mental retardation. Thus phenylketonuria is the best example to explain pleiotropy.

In Drosophila, the vestigial gene is a classic example of pleiotropy, affecting not only wing size but also haltere size, bristle orientation, and reproductive fitness.

E.Nilsson – Ehle crossed red kernelled variety with white kernelled variety of wheat. The grains of F₁ were self crossed among themselves, five different phenotypic classes appeared in F₂ showing the ratio of 1:6:15:20:15:6:1.

These scientist found that the kernel colour in wheat is determined by two pairs of genes A and B. It is called polygenic inheritance.

So, the correct option is ‘polygenic inheritance’.