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 [...]
In this article we will discuss about the molecular structure of centromere. Eukaryotic chromosomes possess a segregational device called centromere which is responsible for the chromosomc movement during cell division. Chromosome fragments without a centromere (acentric fragments) are unable to move to any of the poles during cell division; as a result, they are excluded from the daughter nuclei and [...]