Diploid organisms, such as humans and other mammals, have two copies of their genetic material in the form of homologous chromosomes. One copy of each homologous chromosome is passed to the organism from each of its parents during the process of fertilization. For many genetic traits, a diploid organism is said to be either homozygous or heterozygous at a particular locus, depending on whether its parents passed down two of the same or two different alleles for that specific sequence. Which of the following describes a heterozygous locus?
a) two different alleles are found in a particular position on homologous chromosomes
b) two alleles that are positioned on the same chromosome
c) the alleles at a particular position on homologous chromosomes of an individual with two true-breeding parents for different alleles
d) the alleles at a particular position on homologous chromosomes of an individual who expresses a recessive trait
e) the presence of two or more alleles for a particular trait in the gene pool