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Human chromosomes

Human chromosomes. There are 46 chromosomes (23 homologous pairs) in each somatic cell 22 pairs of autosomes 1 pair of sex chromosomes XX = Female, XY = Male Karyotype - chromosomes are arranged according to shape and size. Nondisjunction and chromosomal disorders.

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Human chromosomes

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  1. Human chromosomes • There are 46 chromosomes (23 homologous pairs) in each somatic cell • 22 pairs of autosomes • 1 pair of sex chromosomes XX = Female, XY = Male • Karyotype - chromosomes are arranged according to shape and size

  2. Nondisjunction and chromosomal disorders • Nondisjunction – failure of chromosomes to separate and segregate into daughter cells • Nondisjunction may occur during meiosis 1 or meiosis 2 • Abnormal number of chromosomes may result

  3. Normal meiosis MEIOSIS I Replicate DNA Results of crossing-over not shown MEIOSIS II Normal monosomic gametes

  4. Nondisjunction during meiosis I MEIOSIS I Replicate DNA Non-disjunction MEIOSIS II Disomic gametes Nullisomic gametes

  5. Nondisjunction during meiosis II MEIOSIS I Replicate DNA MEIOSIS II Non-disjunction Disomic Nullisomic Monosomic Monosomic gametes

  6. EXAMPLES OF NON-DISJUNCTION

  7. AN EXTRA COPY OF CHROMOSOME 21 CAUSES DOWN SYNDROME This condition is called trisomy 21. Person with this condition suffers from the Down syndrome. Characteristic facial features: • Round face • Flattened nose bridge • Small, irregular teeth • Short stature • Heart defects

  8. Klinefelter's syndrome,47, XXY It is the most commonsexchromosome disorderand the second most common condition caused by the presence of extra chromosomes Symptoms: • Language impairment • Lanky, youthful build or rounded body type • Low levels of Testosterone and small testicles / Infertile

  9. Turner’s Syndrome (X) Common symptoms: • Short stature • swelling of the hands and feet • Broad chest and widely spaced nipples • Low hairline • Low-set ears • Reproductive sterility • Increased weight, obesity • Small fingernails • Characteristic facial features • Webbed neck

  10. What genetic disorder is this? They may have never known…

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