Question

Differentiate between linkage and crossing over.

Answer 1

Feature	Linkage	Crossing Over
Definition	Linkage is the tendency of two or more genes located on the same chromosome to remain together during inheritance.	Crossing over is the mutual exchange of blocks of homologous genes between a pair of homologous chromosomes.
Nature	Genes remain physically connected on the same chromosome and tend to be inherited together.	Physical exchange of chromosome segments occurs between non-sister chromatids of homologous chromosomes.
Occurrence	Occurs when genes are located close to each other on the same chromosome and may be complete or incomplete linkage.	Occurs during meiosis I, specifically in the prophase I stage, involving breakage and rejoining of chromatids.
Result	Reduces the possibility of variability in gametes as linked genes tend to be inherited together.	Produces new gene combinations, increasing genetic variability in sexually reproducing organisms.
Example	Complete linkage example: grey body colour and long wings in male Drosophila.	Crossing over can produce recombinant phenotypes different from parental combinations during gamete formation.
Significance	Important in inheritance as it affects gene combinations inherited together unless separated by crossing over.	Important source of genetic recombination and variation, crucial for evolution and micro-evolution.