karyotypes. karyotypes are pictures of homologous chromosomes lined up together during metaphase i...
TRANSCRIPT
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.
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
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Down Syndrome
• Result of having an extra chromosome #21
• Distinctive facial features
• IQ seldom above 70
• Short life expectancy
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
Klienfelter’s Syndrome • 47, XXY male
• 1/500 male live births
• Male genitalia undeveloped, no sperm production
• Female secondary-sex characteristics
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