Nondisjunction: the failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei.
Recessive Genes: is a gene that can be masked by a dominant gene. In order to have a trait that is expressed by a recessive gene, such as blue eyes, you must get the gene for blue eyes from both of your parents. You might remember the word recessive from biology, where it most often appears.
Dominant Genes: is "strong" and always dominates a "weaker" gene. ... A dominant gene masks the effects of a recessive gene, and so recessive traits are only seen when an individual inherits genes that are both recessive - this is expected to occur in one in every four offspring.
Somatic Cell: any cell of a living organism other than the reproductive cells.
Germ cell: a cell containing half the number of chromosomes of a somatic cell and able to unite with one from the opposite sex to form a new individual; a gamete.
Kleinfelter's syndrome: a syndrome affecting males in which the cells have an extra X chromosome (in addition to the normal XY), characterized by a tall thin physique, small infertile testes, and enlarged breasts.
Down Syndrome: a congenital disorder arising from a chromosome defect, causing intellectual impairment and physical abnormalities including short stature and a broad facial profile. It arises from a defect involving chromosome 21, usually an extra copy (trisomy-21).
Colorblindness: happens when someone cannot distinguish between certain colors, usually between greens and reds, and occasionally blues.
Turner's disease: s a chromosomal condition that alters development in females. Women with this condition tend to be shorter than average and are usually unable to conceive a child (infertile) because of an absence of ovarian function