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Describe diploid
- 46 chromosomes in 23 pairs
- 2n
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Meiosis I
- Reductional division
- Diploid --> haploid
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Meiosis II
Equational division
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What is purpose of chiasmata formation?
Recombination of homologous pairs
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Describe the meiotic arrests in oocytes
- Initial arrest at meiosis I at chiasmata/crossing over
- Completion of meiosis I triggered by surge of LH
- Arrest at meiosis II - completed at fertilization (second polar body released)
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Why is increased female age associated with increased abnormalities?
- Longer time period egg remains in meiosis I
- Greater likelihood it will divide unevenly
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Features of Trisomy 21
- Low central tone
- Short stature
- Moderate mental retardation
- Increased chance of cardiac abnormalities, leukemia, Alzheimers
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Features of Trisomy 18
- Profound developmental delay
- Increased tone
- Cardiac, brain abnormalities
- 90% die in first year
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Features of Trisomy 3
- Holoprosencephaly
- Polydactyly
- Severe cardiac, brain abnormalities
- 90% die in first year
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Examples of deletion syndromes
- Cri du chat - 5p segment
- Wolf-Hirshhorn - 4p segment
- Miller-dieker
- Smith-magenis
- Williams
- Prader Willi
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Turner Syndrome
- 45, X
- Short stature, infertility, coarctation of the aorta
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Klinefelter Syndrome
- 47, XXY
- Azoospermia, tall stature, truncal obesity, small testes
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