Explain the reason crossing over can only occur between homo

Explain the reason crossing over can only occur between homologous chromosomes. Use this explanation to determine whether crossing over could take place between sex chromosomes. Provide an example to support your answer.

Solution

A variety of multicellular living organisms possesses 2 sets of homologous chromosomes with diploid nature. Homozygous-both alleles are same and the organism is considered to be as homozygous to that particular gene. Heterozygous-if both alleles are dissimilar then the organism is considered as heterozygous to that particular gene. This phenomenon clearly explained by Hardy-Weinberg law. Therefore, this heterozygosity is persisted in the offspring because of crossing over occur during prophase-I of reduction division mainly between homologous chromosomes. In case of mitosis, crossing over may lead to lose of heterozygosity. Therefore, crossing over could take place between sex chromosomes at the time of generation of gametes through meiosis & this can be explained with linkage phenomenon between genes

Crossing over is somewhat randomly distributed over the length of the chromosome because if the two genes are close together then it is very change to get exchange of chromosomal breaks therefore, if the two genes are located farther apart then there will be higher room for the exchange of genetic material with chromosomal breaks. Therefore, when two genetic are far apart on the same chromosome are more likely to have a crossover between them than two loci that are close together. Linked genes due to linkage often do not obey Mendel\'s laws of inheritance such as independent assortment because of crossing over with reciprocal exchange of hereditary genetic material meticulously in between non-sister chromatids at the time of synapsis formation in reduction division or meiosis 1. These events are leading to formation of gamete cells with complete different genotypically from diploid parent reproductive cell via meiosis finally induce genetic variation in phenotype.

Example,

Sturtevant Alfred (student of Thomas Morgan) has illustrated that crossing over phenomenon was random. However the chances of cross over were equal almost at all specific points on the chromosome. He has elucidated that the distance between genes is more or genes are more apart leading to generation of highest recombination frequency associated with higher chance of probability due to cross over in Drosophila models of sex chromosomes (in this organism, crossing over can only occur between homologous chromosomes). Finally, S Alfred preliminarily assigned specific allelic positions to the chromosomal genes with linkage maps. Genes who are located farther apart on a chromosome have mapped. These gene linkage maps mainly relies upon the addition of recombination frequencies associated with \"crossing over of gene pairs\" locate between two original genes using fruit fly models of homologous chromosomes. In Drosophila models of genes, S Alfred have investigated that genes have clustered mainly in four linked gene groups. They have elucidated that the length of the genes have not accurate with efficient order of genes.