Somatic Crossing Over

Crossing over is also referred as chromosomal crossing over. It helps in exchanging genetic material like DNA between chromosomes. It was first discovered by Thomas Hunt Morgan in the year 1909.  Crossing over can also occur in somatic cells or body cells and also in meiotic phase of cells division. Crossing over is possible only when two identical chromatids are near is capable of splitting up and also reassembles back. It is similar to repair mechanism of DNA. In meiotic crossing over synaptonemal complex is formed which is not seen in somatic crossing over. Meiotic crossing over is not much prevalent. Somatic crossing is also called as mitotic crossing over.

Mitotic crossing over or Somatic crossing over

Mitotic crossing over is evident in fungus Aspergillus nidulans. Its occurrence is obvious once in 100 cell divisions. Mitotic cross over occurs when sexual cross over is not possible where chromosomal cross over generates genetic variation during meiotic cell division. It is seen in diploid cells. Mitotic Chromosomal cross over requires a pair of chromosomes. It occurs in somatically or asexually produced organism like fungi and other eukaryotic cells like humans. Mitotic recombination is a genetic recombination which is seen in somatic cells during mitosis stage. The concept of mitotic recombination is discovered by Curt Stern in the year 1936 in fruit fly Drosophila melanogaster. This recombination is induced by X- ray and site directed recombination system.

Instance of somatic crossing over

Curt Stem observed twin spot occurrences in Drosophila melanogaster. Dihybrid is formed between single allele for bristle appearance and single allele for yellow colour in body. When yellow colour allele crosses over centromere twin spot is formed. When single allele for bristle appearance crosses over with yellow color allele a double spot is formed. When double cross over of single allele for yellow color and bristle with yellow colour and centromere occurs, it results in formation of single spot. Three types of phenotypic changes are possible by mitotic recombination.

Applications of mitotic cross over

Mitotic recombination helps in better understanding of fungal genetic. Chromosomal crossing over aids in determination of genetic linkage.