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 21 st 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 Syndrome Typical 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