In flies, red eyes (r) are dominant to brown eyes (r). a heterozygous fly is crossed with a homozygous recessive fly

The cross of a heterozygous fly with a homozygous fly can be shown as follows:

         r            r

R      Rr           Rr

r        rr            rr

The results show that there is a 50% probability that the flies produced will have red eyes. Their genotypes will be heterozygous.

The results of the punnet square show that there will be a 50% probability that the offsprings will have brown eyes. Their genotype will be homozygous recessive.

A homozygous trait can be described as a trait which has same alleles for the gene which encodes the trait. Heterozygous means that both the alleles for the trait will be different.

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.