Answer :
The correct answer is A. Homologous chromosomes with heterozygous alleles.
If the alleles of genes are different then the scientist is observing for homologous chromosomes with heterozygous alleles.
In each homologous pair there is one chromosome which comes from maternal chromosome and the other one from paternal chromosome.
Homologous chromosomes are not identical but they are similar. Alleles for each homologous chromosome is not same but genes are the same.