as nucleotide base sequences that make up genes
to study how different species are related to each other
down syndrome
the 2 alleles of the gene for the trait are different on the 2 homologous chromosomes
Being heterozygous for a trait means that they have different alleles for a trait. For instance: Tt would be heterozygous and TT or tt would be homozygous because they are both eitehr little or big t's.
it mean the gene is not pure or for example suppose a person is blood group A but actually he is having A and O; because O is recessive trait the gene express the A trait instead, making the person having blood group A.
Nuclear regulatory commission - A+