Question

Define complete linkage? Give an example of cross, showing complete linkage?

Answer 1

Linkage is a divergence from the Mendelian self-assortment theory. It may be useful in assessing the patterns of inheritance of the main psychological condition disorders, such as anxiety, bipolar disorder, and dementia.

Complete answer:
In 1910, Morgan announced "Chromosome Theory of Linkage" while working on Drosophila, claiming that coupling and repulsion are two aspects of the association. He defined complete linkage as the tendency of genes present in the same chromosome to remain in their original combination and enter together without crossover into the same gamete. Gens are closely linked in this form of association, and appear to stay together.

The strength of the association can be measured by the distance between two genes, i.e., the greater the distance, the strength of the association would be lower. During meiosis, the attachment is broken down by the act of crossing over. If genes are so closely connected that they are still expressed together, they are not crossed over, the relation between them is called complete as illustrated in an example below:

Where a male Drosophila and female silkworm (Bombyx mori) have 100% Parental combinations showed that the body color gene is entirely correlated with long wings. The phenotypic F2 ratio in this dihybrid is 3:1, and the test cross-ratio is 1:1 (like a monohybrid).

In the case of male Drosophila recombinant forms are absent due to lack of crossing over. This means that in their original configuration all the genes that originate on a single chromosome will end up on the same chromosome. Only parental phenotypes are predicted, in the absence of recombination.

Note: Morgan was first linked to the division of homologous chromosomes and the phenomenon of meiosis passing between homologous chromosomes. Linkage decreases the likelihood of gametes variability unless there is crossing over.