When flies having a gray body and normal wings were crossed with flies having a black body and vestigial wings, the F2 generation showed a phenotypic ratio of 3:1, and not 9:3:3:1.

This proves Gregor Medel's hypothesis.

Explanation:

When Gregor Mendel crossed two pure-breed flowers, he noticed that the offspring in the F1 generation exhibited all dominant traits. However, when he crossed the offspring in the F1 generation, he noticed that the recessive trait reappeared in a 3:1 ratio (one reccesive). This is because for each trait, one allele from each parent is passed on. Also, the alleles are passed independently of one another, meaning that one allele passed for one trait won't affect the chance of another.

the diploid number of chromosomes is sometimes represented by the symbol 2n. for the fruit fly, the diploid number is 8, which can be written as 2n = 8, where n represents twice the number of chromosomes in a sperm or egg cell.