Linkage and Crossing Over

Linkage and Crossing Over

- Linked genes are those located close together on the same chromosome.

- They tend to be inherited together, which deviates from Mendel's principle of independent assortment.

- The phenomenon of crossing over, which occurs during meiosis, can break the linkage between genes.

- Crossing over involves the exchange of genetic material between homologous chromosomes, increasing genetic diversity.

-Linkage describes the physical association of genes on a chromosome, leading to deviations from the expected Mendelian ratios when they are inherited together. In contrast, crossing over is a genetic phenomenon that can break the linkage between genes on the same chromosome.

Morgan's Experiments on Linkage and Crossing Over:

- Morgan recognized that genes located on the same chromosome tended to be inherited together more often than not.

- He introduced the term "linkage" to describe this phenomenon.

- He also introduced the term "recombination" to describe the generation of non-parental gene combinations when crossing over occurred during meiosis.

- Morgan's group found that not all linked genes had the same degree of linkage; some were tightly linked (showing low recombination), while others were loosely linked (showing higher recombination).

- For instance, the genes white and yellow in Drosophila were very tightly linked with only 1.3% recombination, while white and miniature wings showed 37.2% recombination.

- Alfred Sturtevant, Morgan's student, used the frequency of recombination as a measure of the distance between genes and created genetic maps to depict their positions on chromosomes.

 

 

These discoveries by Morgan and his group provided important insights into the concepts of sex linkage, linkage, and crossing over, expanding our understanding of genetic inheritance.