Assuming that all 4 gametes were fertilized by normal

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Unformatted text preview: missing a chromosome. The risk of trisomy 21 increases with the age of the mother Risk of a 48 year old woman to have a child with trisomy 21 is 1/14, and any chromosomal aberration is 1/10! Clicker question A non-disjunction of Chromosome 21 occurs in meiosis I of an oocyte (egg cell). Assuming that all 4 gametes were fertilized by normal sperm cells, what would the karyotypes of the resulting zygotes (early embryos)? A.  2 zygotes with normal karyotype, 1 monosomic for Chr. 21, one trisomic for Chr. 21 B.  3 zygotes with normal karyotype, one trisomic for Chr. 21 C.  2 zygotes trisomic for Chr. 21, two monosomic for Chr. 21 D.  All 4 normal, because only non-disjunction in meiosis can result in trisomy Trisomy 21, 13, and 18 are the only three human autosomal anneuplod genotypes where some babies survive to birth Trisomy 13, Patau syndrome, very few survive to birth, many are mosaic for the trisomy genotype, cleft palate, brain developmental defects, feeding difficulties, extra fingers and or toes (polydactyly) frequency- 1/10,000 live births) Trisomy 18, Edwards syndrome, half die prior to birth, joint contractures, poor developmental delays, difficulty in feeding and breathing, mental retardation, small head (microcephaly), frequency 1/3000 live births Why don t we observe trisomies of other chromosomes? Embryos that have them do not survive to birth. It is estimated that 1/2 to 2/3 of human conceptions do not develop successfully to term. Chromosomal abnormalities are thought to be the cause for most naturally terminated pregnancies....
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This note was uploaded on 01/07/2013 for the course BIMM 100 taught by Professor Pasquinelli during the Spring '06 term at UCSD.

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