Introduction to Genetic Analysis 508

Introduction to - syndrome is a parent heterozygous for a Robertsonian translocation involving chromosome 21 Meiotic segregation results in some

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507 1,000,000 conceptions 150,000 spontaneous abortions 850,000 live births 833,000 children 17,000 perinatal deaths 5165 chromosome abnormalities 500 unbalanced structural aberrations 117 inversions 758 balanced reciprocal translocations 758 balanced Robertsonian translocations 1849 sex chromosome aneuploids 1427 males 422 females 1183 autosomal trisomics 42 trisomy 13 100 trisomy 18 1041 trisomy 21 75,000 chromosome abnormalities 5250 others 4500 tetraploids 12,750 triploids 13,500 XO 39,000 trisomics (3510 trisomy 21) Figure 15-33 The fates of a million implanted human zygotes. [From K. Sankaranarayanan, Mutation Research 61, 1979.] Figure 15-34 One origin of Down syndrome. In a small minority of cases, the origin of Down
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Unformatted text preview: syndrome is a parent heterozygous for a Robertsonian translocation involving chromosome 21. Meiotic segregation results in some gametes carrying a chromosome with a large additional segment of chromosome 21. In combination with a normal chromosome 21 provided by the gamete from the opposite sex, the symptoms of Down syndrome are produced even though there is not full trisomy 21. Translocation carrier Normal Lethal Down syndrome Gametes from normal parent Gametes from translocation carrier Breaks 21 21 14 14 ( ) lost Normal progenitor Robertsonian translocation carrier Meiotic pairing 44200_15_p481-520 3/12/04 1:07 PM Page 507...
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.

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