Question

Linkage and crossing-over of genes are alternatives to each other. Justify with the help of an example?

Answer 1

Hint: Gene is a basic unit of hereditary which is transferred from parents to their offspring.
They are found in the chromosomes present inside the living cell.

Complete answer:
In order to solve this question we need to know about linkage and crossing over.

Chromosome: chromosomes are the thread like structure, found in the nucleus of the living cells.
- The structure consists of nucleic acids and proteins.
- They carry genetic information in the forms of genes.

Linkage: It is a closer association of genes that are present on the same chromosome.
- Closer the gene, more will the probability of their inheritance.

Crossing over: It is alteration in genes of homologous chromosomes resulting in mixing of parental features or characters in their offspring.
- Crossing over accounts for the genetic variations.
- Linkage and crossing over is alternative to each other because linkage is the tendency of genes to stay together during transmission, whereas crossing over is exchange of segments of homologous chromosomes which results in variation.

In drosophila, a brown bodied red-eyed male is crossed with the yellow bodied white eye female and after crossing them we will get f1 progeny, now f1 progeny gets intercrossed and we get f2 whose phenotypic ratio will be 9:3:3:1.

The gene for body color and eye color is present on the ‘x’ chromosome which shows linkage and inheritance.
Recombinants are also formed due to crossing over but at a low percentage.

Note: Human genome project is a research program whose main motive was to complete mapping and to understand all the genes of the human being.
All human genes are together known as Genomes.