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 [...]
The following points highlight the four main types of permanently specialized chromosomes. The types are: 1. Nucleolar Chromosomes 2. Sex Chromosomes 3. B Chromosomes 4. Chromosomes with Diffuse or Multiple Centromeric Regions. Permanently Specialized Chromosomes: Type # 1. Nucleolar Chromosomes: The chromosome forming the nucleolus (plural = nucleoli) is called the nucleolar chromosome. Normally one or more chromosomes in the [...]
In this article we will discuss about the relationship between genetic and cytological crossing over. The exchange of homologous segments of chromatids between homologous chromosomes during meiosis was cytologically demonstrated by Stern in 1931 in D. melanogaster and by Creighton and McClintock in the same year in maize. Stern used stocks of D. melanogaster carrying chromosomal structural changes. These stocks [...]