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25 Cards in this Set
- Front
- Back
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Turner syndrome have?
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45 X
Missing another X |
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Klinefelter male have?
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47, XXY
Have an extra X |
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X-inactivation
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There are many genes on the X chromosome, but each individual only requires expression of one X chromosome
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Pseudoautosomal regions
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Every chromosome contains terminal regions that are important and must be retained in their activated state, even if the rest of the chromosome is inactivated.
We know this because people w/o both pseudoautosomal regions have Turner's or Klinefelter's syndrome) This region pairs during meiosis and crossing over takes place |
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If crossing over does not occur in the pseudoautomosal region, then what can occur?
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XX male (have male-determining Y sequences on one X chromosome)
XY female (contain a Y crhomsome that has lost the male-determining sequences) |
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Is x-inactivation random?
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Generally random, except if there is an abnormal x-chromosme then that will be inactivated
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When does non-random X inactivation occur?
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X: autosomal translocations
Normal X is inactivated since the X involved in the translocation carries some autosomal genes |
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The most common live-born trisomy and is the single most common genetic cause of moderate mental retardation?
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Trisomy 21
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Incidence of Trisomy 21 (down syndrome)
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1/800 with a higher incidence in children of mothers over 35.
Occurs during nondisjunction of Meiosis I |
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Phenotype of Trisomy 21 (down syndrome)
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-flat facial profile (cheeks/chin not developed)
-first abnormality noticed is hypotonia -epicanthal folds -brachycephaly -ears have characteristic folded appearance -mouth usually open showing protruding tongue -congenital heart disease is present in 40% of all live-born down syndrom infants so you SHOULD order a cardiac evaluation -Holoprosencephaly of brain -Endocardial cushion defects (septum btw R & L doesn't close) -gastrointestinal atresias -High risk of Alzheimers Disease |
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How is Trisomy 21 (Down Syndrome) caused?
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95% of Down syndrom is following nondisjunction parimarily in maternal meiosis
4% have robertsonian translocation (fusion of two 21 long arms) |
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Incidence of Trisomy 18 (Edwards Syndrome)
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1/6,000 live births
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What percent of Trisomy 18 (Edwards Syndrome) will not survive?
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90-95% will not survive because they often stop breathing in the middle of thenight
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Phenotype of Trisomy 18 (Edwards Syndrome)
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-Hypertonia
-Fists are clenched with 2nd & 5th digits overlapping the third & fourth. -small nails -low set malformed ears -rocker bottom feet -Micrognathia (small lower jaw), microcephaly, and syndactyly (union of 2 or more digits) |
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When some cells are affected and others are not, then kids could be minimally affected
-to detect this, take cells from multiple areas of the body to prepare karyotypes |
Mosaiacism
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Incidence of Trisomy 13 (pataus syndrome)
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1/10,000 live births (less common than Trisomy 18)
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Phenotype of Trisomy 13 (pataus syndrome)
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-mental retardation
-micropthalmia (small eyes) -holoprosencephaly -polydactyly (extra digit) -Cyclopia (single eye) -Cleft lip/palate -death is inevitable |
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Percent of Trisomy 13 survival?
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50% die within first month, and only 18% survive first year.
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Abortuses most commonly have what Trisomy?
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Trisomy 16
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Klinefelter syndrome
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XXY (although one X is inactivated except for the pseudoautosomal regions)
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Phenotype for Klinefelter syndrome
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-Tall and then, long legs
-appear normal before puberty -small testes & hypogonadism -infertile -intelligence problems |
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Turner syndrome
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-Girls with XO
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Phenotype of Turner Syndrome
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-short stature
-webbed neck -shield-shaped chest -gonadal dysgenesis -aortic stenosis -Edema due to lymph system not working corectly |
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The majority of errors in women occur?
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75% of maternal meiosis errors of MI
25% are MII |
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The X thatis presentin a 45, X conceptus is the maternal X what percent of time?
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80%
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