Q.Write the differences between linkage and Crossing over.

Linkage is genes on the same chromosome tending to be inherited together; crossing over is the physical process during meiosis that exchanges chromosome segments and thereby breaks that linkage, producing recombinants.

Linkage

Genes located on the SAME chromosome, especially if they lie close together, tend to be transmitted together to the next generation as a group, rather than assorting independently as predicted by Mendel's law of independent assortment (which strictly applies only to genes on different chromosome pairs). This tendency of genes to stay together is called linkage, and it results in a higher-than-expected proportion of parental-type (non-recombinant) gametes/offspring, and a correspondingly lower proportion of new (recombinant) combinations.

Crossing over

Crossing over is the actual cytological mechanism responsible for breaking up linked gene groups. It occurs during prophase I of meiosis (specifically at the pachytene stage), when homologous chromosomes are closely paired (synapsis) and non-sister chromatids physically break at corresponding points and exchange (reciprocally) the broken segments, at points visible as chiasmata. This exchange produces new combinations of alleles on a chromosome that did not exist in either parent, i.e., recombinant chromatids.

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