What are alleles?

Alleles are variants of the same gene that occur on the same place on a chromosome. They are alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.

If the alleles at a gene locus on the homologous chromosomes are the same, then that organism is homozygous with respect to that gene. If the alleles are different, then they and the organism are heterozygous with respect to that gene. A given gene may have multiple different alleles, though only two alleles are present at the gene’s locus in any individual.

1. alleles are found at the same locus on chromosomes. -part of the definition of alleles is that they are alternative forms of a gene. alleles therefore must be found at that genes locus. choice a. is incorrect; multiple alleles are common in populations. choice c. is incorrect and misleading; it is true only of diploid cells.

haploid cells (gametes, haploid somatic cells from organisms such as mosses), of course, cannot possess more than one allele of a gene. choice d. is incorrect, since even a diploid individual is restricted to possessing two different alleles of a gene. choice e. is completely false.