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Chromosomes 2

Chromosome Number All cells in the human body (SOMATIC CELLS) have 46 or 23 pairs of chromosomes Called the DIPLOID or 2n number GAMETES (eggs & sperm) have only 23 chromosomes Called the MONOPLOID or 1n number 3copyright cmassengale

Nondisjunction Chromosomes may 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 4copyright cmassengale

Normal Male 5 2n = 46 copyright cmassengale

Normal Female 6 2n = 46 copyright cmassengale

Male, Trisomy 21 (Down’s) 7 2n = 47 copyright cmassengale

Female Down’s Syndrome 8 2n = 47 copyright cmassengale

Trisomy 21—Down’s Syndrome Three copies of chromosome 21 Maternal Age Incidence at Birth 201 in in in in in 30

Klinefelter’s Syndrome 10 2n = 47 copyright cmassengale

Klinefelter’s Syndrome Male—XXY 1 in 1000 males Sterile Tall, thin, and slightly lower IQ

Turner’s Syndrome 12 2n = 45 copyright cmassengale

Other Disorders Turner’s Syndrome—XO 1 in 500 female births (most are aborted before birth) Very short, infertile, broad chest and may have a webbed neck Edward’s Syndrome—Trisomy 18 1 in 3000 Most babies die within the first month to the first year