Q.The cross which proves that sex has no influence on inheritance is:

Reciprocal Cross

When breeders want to be sure a trait is inherited the same way regardless of which parent carries it, they perform a reciprocal cross. The idea is elegantly simple: run the same cross twice, but swap which sex carries which trait.

What a reciprocal cross actually is

Suppose you cross a tall plant with a dwarf plant. There are two ways to set it up:

• Cross 1: tall female × dwarf male
• Cross 2: dwarf female × tall male

Together these two crosses — the same pair of contrasting traits but with the sexes of the parents reversed — form a reciprocal cross.

Why bother reversing the parents?

The purpose is to test whether the sex of the parent affects inheritance. For an ordinary autosomal trait (one carried on a normal, non-sex chromosome), it should not matter at all which parent was tall and which was dwarf — the offspring ratios come out identical both ways. Mendel found exactly this: his reciprocal crosses gave the same results, confirming that his traits were inherited independently of the parent's sex.

When results differ — the interesting case

A reciprocal cross becomes revealing when the two directions give different results. This happens for:

• Sex-linked traits (genes on the X or Y chromosome) — a classic example is eye colour in Drosophila, where a reciprocal cross gives different outcomes depending on which parent carried the trait. …