Genetic variation

Genetic differences reflect the genotypeof an organism, that is, its genetic make-up. A diploid organism has two sets of chromosomes and two forms (alleles)of each particular gene. These alleles may be the same (the organism is homozygous for that gene) or different (the organism is heterozygousfor that gene). If different, one of the alleles (the dominant allele)may mask the other allele (the recessive allele).The dominant allele is therefore expressed in either the heterozygous or the homozygous condition, whereas the recessive allele is expressed only in the homozygous condition. If an organism is haploid (that is, it has only one set of chromosomes), all its alleles will be expressed and will be reflected in its observable or measurable characters(the features or traits transmitted from parent to offspring).