5. What happens if a homologous pair of

5. What happens if a homologous pair of

5. What happens if a homologous pair of chromosomes fails to separate, and how might this contribute to genetic disorders such as Down syndrome, Turner syndrome, or Klinefelter syndrome? NONDISJUNCTION- failure of homologous chromosomes/chromatids to separate

Results in cells with missing or extra chromosomes Down syndrome- Trisomy 21 (three #21 chromosomes) Klinefelter syndrome- XXY males Turner syndrome- XO females Homologous chromosomes/chromatids fail to

separate during MEIOSIS NONDISJUNCTION = _________________________ One cell gets 2 copies of the chromosome the other cell gets none. Normal Meiosis

Nondisjunction http://web.udl.es/usuaris/e4650869/docencia/gen_etica/meioferti2.html http://www.tokyo-med.ac.jp/genet/anm/domov.gif Nondisjunction Nondisjunction Since it happens to a

sperm or egg, the new baby can end up with _____________ 3 copies of a chromosome = ________________ TRISOMY OR only ___________ of a one copy

chromosome = _________________ MONOSOMY Human Abnormalities caused by NonDisjunction Down syndrome __________________

Klinefelter syndrome __________________ Turner syndrome __________________ 21 Down syndrome (=TRISOMY ____________)

Down syndrome (Trisomy 21) 1 in 800 births Similar facial features Slanted eyes Protruding tongue Down syndrome (Trisomy 21) Simian line on palm

Down syndrome (Trisomy 21) Most common chromosomal abnormality 50% have heart defects that need surgery to repair Mild to severe mental retardation Increases susceptibility to many diseases

Risk of having a child with Down syndrome increases with age of mom Down syndrome (Trisomy 21) Risk of having a child with Down syndrome related to age of mom More common in

women UNDER 16 or OVER 35 Cells that make eggs start meiosis in embryo Stop in PROPHASE I (synapsis) One egg restarts & finishs division each month So an egg released at age 40 has been in synapsis f 40 years . . . chromosomes more likely to stick

Turner syndrome Turner syndrome XO ____ 1 in 5000 births Females have only one X chromosome Small size Slightly decreased intelligence

35% have heart abnormalities Hearing loss common Broad chest Reproductive organs dont develop at puberty Cant have children http://medgen.genetics.utah.edu/photographs/diseases/high/611.gif

Klinefelter syndrome XXy Klinefelter syndrome 1 in 1000 births Males have extra X chromosome (XXY) (can have more than 2 Xs) Feminized characteristics 20% slight breast development less facial/body hair after puberty

Average/slight decrease in intelligence Small testes/cant have children Usually not discovered until puberty when dont mature like peers

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