The below mentioned article provides a short note on mitotic crossing over. Crossing over not only occurs during meiosis but also during mitosis. In individuals heterozygous for a gene producing a visible phenotype, somatic crossing over leads to the production of "twin spots" of dominant and recessive phenotypes. Mitotic crossing over was first discovered in Drosophila by Stern in 1936, [...]
The following points highlight the two main adaptational forms of chromosomes. The forms are: 1. Polytene Giant Chromosomes 2. Lampbrush Chromosomes. Form # 1. Polytene Giant Chromosomes: Polytene giant chromosomes are normal interphase chromosomes where homologues become paired and undergo several replications; all the copies so produced remain associated together. Polytene giant chromosomes are typically found in salivary gland cells [...]
In this article we will discuss about the molecular basis of crossing over. Any molecular model of crossing over must accommodate the explanation of the following phenomena: (a) Gene conversion, (b) Post-meiotic segregation, (c) Polarized conversion and (d) Negative interference. a. Gene Conversion: It is the unequal recovery of alleles in the region of exchange during genetic recombination in cases [...]