Biology XII:5 Prin of Inher & Vari(10 Chromosomal Disorders)

Chromosomal Disorders Total number of chromosomes in humans = 46 (23 pairs) Total 23 pairs = Autosomes (22 pairs) + Sex chromosomes (1 pair) Monosomy − Lack of any one pair of chromosomes Trisomy − Inclusion of an additional copy of chromosome Aneuploidy − Loss or gain of chromosomes due to the failure of segregation of chromatids during cell division Down’s Syndrome Cause: Presence of an additional copy of chromosome 21 (Trisomy of 21) Affected individual has short stature, small, round head, furrowed tongue, partially opened mouth, palm crease, congenital heart disease and mental retardation. Klinefelter Syndrome Cause: Additional copy of X chromosome, i.e., 47 chromosomes (XXY) Affected individual has an overall masculine development with gynaecomastia; individual is sterile Turner’s Syndrome Cause: Absence of one X chromosome, i.e., 45 chromosomes (XO). Affected females are sterile; have rudimentary ovaries; secondary sexual characters are absent