Question

Define linkage. Explain the effect of linkage on inheritance of two genes.

Hint:

Genes that sit close together on one chromosome do not assort independently; think about what that does to the offspring ratios.

Answer 1

Step 1: Define linkage.
Linkage is the tendency of two or more genes located close together on the same chromosome to be inherited together, as a group, rather than independently, because they travel together on that one chromosome during gamete formation.

Step 2: Contrast with Mendel's independent assortment.
Mendel's law of independent assortment holds only for genes on different chromosomes (or far apart on the same one); it predicts free recombination and a 9:3:3:1 dihybrid ratio. Linked genes break this rule because they mostly move together.

Step 3: Explain the effect on inheritance.
Because linked genes are usually passed on together, the parental combinations of traits show up in the offspring far more often than the new (recombinant) combinations. Only occasional crossing over between the linked genes creates some recombinant offspring, so the observed ratio deviates sharply from the free 9:3:3:1 ratio, skewed toward the parental types.

Final Answer:
Linkage is co-inheritance of genes lying close on the same chromosome; it makes parental trait combinations appear far more often than recombinant ones, distorting the expected dihybrid ratio.