GENETIC DISORDERS

Mutation –change in a gene resulting in change in genetic information may be spontaneous or caused by a mutagen Somatic mutations are usually not noticed Gametic mutations are more severe Not all mutations are bad!

SINGLE-GENE DEFECTS Congenital Defects: Inherited Misplacement, insertion or deletion of one base pair May result in incorrect amino acid May result in shift of reading frame Congenital Defects: Visible at birth(club foot, spina bifida, congenital heart defects) Caused by environmental factors (FAS, German measles) Inherited Sickle Cell Anemia, Cystic Fibrosis

INVERSIONS Part of chromosome is flipped around 180° from its normal orientation. Happens when chromosome breaks occur. Broken piece may reattach, but not necessarily in the same orientation as before

TRANSLOCATIONS Detachment of a segment of a chromosome, and reattachment to another non-homologous chromosome. Some genes wind up on a completely different chromosome

ANOMALIES OF CHROMOSOME NUMBER Polyploidy is common in plants Gametes don’t reduce chromosome # Result in cells with multiple copies of the genome

ANOMALIES OF CHROMOSOME NUMBER Aneuploidy – more common in humans Usually lethal before or shortly after birth Monosomic and Trisomic

NONDISJUNCTION Occurs when homologous chromosomes fail to separate after synapsis Most nondisjunction events are lethal to the fetus

DOWNS SYNDROME Results from a third copy of chromosome 21 Called a trisomy Individuals have 47 chromosomes in every body cell

SEX CHROMOSOME NONDISJUNCTION DISORDERS TURNER SYNDROME Occurs when nondisjunction causes a gamete to have a missing sex chromosome (X O) Sterile females 1 in 10 000 live births

SEX CHROMOSOME NONDISJUNCTION DISORDERS KLINEFELTER’S SYNDROME Genotype of XXY (extra sex chromosome) Sterile males, breast development 1 in 800 live births

SEX CHROMOSOME NONDISJUNCTION DISORDERS XY ½ ½ gamete lacking a sex chromosome XO ¼ Turner’s syndrome YO ¼ Will not survive (LETHAL CONDITION) ½ gamete formed from nondisjunction XXX ¼ “super female” usually normal XXY ¼ Klinefelter’s syndrome X Y O XX XX