Genetics and Plant Breeding

Independent assortment leads to separation of genes and is a violation of genetic linkage. Crossing over leads to exchange of fragments between two homologous chromosomes and results in the formation of chiasmata. The mutation is sudden lethal changes in a chromosome or genetic material that is often lethal. SO, all of these result in variations in genetic material.

A.cis – arrangement - two dominant alleles linked on one chromosome is called cis arrangement of genes.

B.Trans arrangement – two dominant alleles present on different chromosomes is called trans arrangement of genes

C.Partly cis partly trans – dominant alleles partly present on same chromosomes and partly present on different chromosomes.

So, the correct option is ‘cis arrangement’.

The garden pea, Pisum sativum was the model system used by Gregor Mendel to formulate his famous Mendel's laws. But the characters used by Mendel have been since shown to be controlled by genes belonging to different linkage groups or to distant parts of the same linkage group. Thus, Mendel failed to observe the phenomenon of linkage. Instead, linkage was first described and interpreted by Thomas Morgan in his works with Drosophila. Linkage in pea was first described in 1912 by Vilmorin and Bateson. Thus if the history of pea genetics begins with the Gregor Mendel, the history of the pea linkage map begins much later. There are seven linkage groups in pea; present on chromosomes 1, 6, 5, 7, 3, 2 and 4 respectively. So, the correct answer is '7'.

Mendel studied 7 characters in pea plant. The genes for these characters were located on 4 chromosomes. Mendel was lucky enough as none of the genes showed linkage and assorted independently. This is because the genes studied were located far apart on the same chromosome and thus, expressed independently. 

Genetic linkage is the tendency of alleles that are located close together on a chromosome to be inherited together during meiosis. Genes whose loci are nearer to each other are less likely to be separated onto different chromatids during chromosomal crossover, and are therefore said to be genetically linked. In other words, the nearer two genes are on a chromosome, the lower is the chance of a swap occurring between them, and the more likely they are to be inherited together. Linkage of genes in animals and plants is seen as deviations from independent segregation; recombination seen as deviation from complete linkage.
More linkage between genes, lesser will be the recombination frequency.

Genetic linkage is the tendency of alleles that are located close together on a chromosome to be inherited together during meiosis. Genes whose loci are nearer to each other are less likely to be separated onto different chromatids during chromosomal crossover, and are therefore said to be genetically linked. In other words, the nearer two genes are on a chromosome, the lower is the chance of a swap occurring between them, and the more likely they are to be inherited together.

Linkage is referred to the phenomenon wherein alleles located close together on a chromosome show tendency to be inherited together during meiosis. Genes present near to each other have less probability of being separated onto different chromatids during chromosomal crossover. Therefore, when a cluster of genes show linkage behaviour they do not show independent assortment. Genes showing linkage behaviour do not assort independently and hence, do not show recombination during meiosis. Linkage map shows relative position of genes on the chromosomes based on recombination frequency between them; the map show both linked and independently assorted genes. 

When the genes are present on the same chromosomes they are said to be linked. When gene remains together for two or more generation they are said to have complete or perfect linkage. Thus the bond between them becomes strong. Thus, the correct answer is option A.

Linkage is the tendency of alleles present close to each other to be inherited together during meiosis and hence they show parental combinations. But since complete linkage occurs rarely, sometimes the linked genes separate during meiosis and new combinations are formed. Hence, option B is correct.

Linkage is the tendency of genes present close on the chromosomes to be inherited together and not to assort independently in the offspring. It gives only parental combinations in the offspring. Since, complete linkage is a rare phenomenon, the linked genes sometimes show tendency of independent assortment and results in production of new combinations in offspring in lower percentage. Hence, production of parental characters combinations in the offsprings of a dihybrid in excess to non-parental combinations is due to "linkage". Option "C" is correct.

The frequent occurrence of the phenomenon leading to the trait 'deafness' in
cats being associated with cats with 'white coat color' is possible only in the case when the alleles for these traits are so close together on a chromosome that they are inherited together during the meiosis phase. This tendency of the alleles to be inherited together is known as genetic linkage or gene linkage. Thus, the correct answer is option A.

Tendency of genes located on the same chromosome, to stay together in hereditary transmission, is known as linkage. The genes located on the same chromosome are called as linked genes.

Mendel's law of independent assortment is not applicable for the genes which reside on the same chromosome. He was able to interpret the results and give out the laws because the 7 pair of contrasting characters which he chose in pea were residing on different chromosomes. 

In a dihybrid cross, independent assortment would yield a 9:3:3:1 ratio. The observed data shows a massive deviation with high parental types (tall/hairy and short/smooth) and very few recombinants, which is indicative of linked genes.