Karyotypes

Karyotypes• Karyotypes are pictures of

homologous chromosomes lined up together during metaphase I of meiosis.

• There are 44 autosomes and 2 sex chromosomes in the human genome, for a total of 46.

• Chromosomes are photographed, enlarged, then cut apart and arranged in pairs.

• Photos are arranged by size (length) and location of the centromere.

Human Karyotype

Nondisjunction

•Chromosomes fail to separate during meiosis

•Resulting gametes may have too few or too many chromosomes

•Disorders:–Down Syndrome – three 21st chromosomes–Turner Syndrome – single X chromosome–Klinefelter’s Syndrome – XXY chromosomes

4

Down Syndrome

• Result of having an extra chromosome #21

• Distinctive facial features

• IQ seldom above 70

• Short life expectancy

Down SyndromeTypical Karyotype

Turner’s Syndrome • XO female, missing one X

• 1/3000 female live births

• Ovaries undeveloped, sterile

• Short stature, shield-like chest, webbed neck

• Normal intelligence

Turner’s Syndrome Karyotype

Klienfelter’s Syndrome • 47, XXY male

• 1/500 male live births

• Male genitalia undeveloped, no sperm production

• Female secondary-sex characteristics

Klienfelter’s Syndrome Karyotype

XXX Condition

• 47, XXX female• 1/1200 female live births• Variable phenotype, frequently normal, may be sterile, may show mental retardation • Under-developed secondary sex characteristics• Many institutionalized

XYY Condition

• 47, XYY male• 1/1000 male live births• Above-average height, 2% in maximum security prisons are XYY, personality disorders, subnormal intelligence• Fertile• Many XYY males socially normal