Nondisjunction:An accident of meiosis or mitosis, in which both members of a pair of homologous chromosomes or both sister chromatids fail to move apart properly.
Recessive Genes:A gene that is expressed only when it is present in two copies or if theother copy is missing.
Dominant Genes: (Of, or pertaining to) An allele or a gene that is expressed in an organism’s phenotype, masking the effect of the recessive allele or gene when present.
Somatic Cell any cell of a living organism other than the reproductive cells.
Germ cell Either the egg or the sperm cell; a reproductive cell. Each mature germ cell is haploid, meaning that it has a single set of 23 chromosomes containing half the usual amount of DNA and half the usual number of genes. Except for the egg and the sperm, most cells in the human body contain the entire human genome. Also known as a gamete.