red blood cell: a mature blood cell that contains hemoglobin to carry oxygen to the bodily tissues; a biconcave disc that has no nucleus
somatic cell: any of the cells of a plant or animal except the reproductive cells; a cell that does not participate in the production of gametes
testcross: a cross between an organism whose genotype for a certain trait is unknown and an organism that is homozygous recessive for that trait so the unknown genotype can be determined from that of the offspring