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Practice_MidtermKeyF11 - Bio D137 Human and Eukaryotic...

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Bio D137 Human and Eukaryotic Genetics J.L.Marsh F'11 Practice MidTerm questions Name/student ID:_______________ 1 1) Non disjunctionConsider chromosome 13 of humans. Assume in one marriage the parents are 13 a 13 b (male) and 13 c 13 d (female), where a, b, c, and d stand for cytologically detectable polymorphic alleles of an enzyme that maps on chromosome 13. Fetuses of the following types are produced: (42A stands for the rest of the autosomes.) a] 42A + 13 a 13 c 13 c + XY b] (42A + 13 d + XX); (42A + 13 a 13 d + XX); (42A + 13 a 13 a 13 d + XX) For each fetus, describe with carefully labeled diagrams the events that gave rise to the condition. Points are given for the diagram demonstrating what is going on. State in which individuals the events took place. C] Would you expect one of these children to be less severely affected than the other and if so, which one and why? Answer : a] (8 pts.) This fetus could arise by Non-disjunction of chr. 13 in Meiosis II of the mother b] (8 pts.) This fetus is mosaic (i.e. 3 types of cells are found) and could arise by mitotic non- disjunction of chr. 13 (specifically the paternal chr. 13 a ) It may also be noted that this mitotic ND must have occurred after the first cell division, as there would otherwise be no normal cells present. c] ( 4 pts.) the second child is a mosaic and thus some of his cells are normal. I would expect him to be less severely affected. Also, the extent of the effect of the mitotic nondisjunction in b depends in large part on when in development it occurred, and in what tissues. Any answer that incorporates these ideas into a good argument earns full credit HOWEVER – some students argued that child b is hemizygous in some cells and thus this Loss of Heterozygosity may cause a more severely affected phenotype, though not by the trisomy. Credit was also given for this argument as well. . -3pts if no diagram
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Bio D137 Human and Eukaryotic Genetics J.L.Marsh F'11 Practice MidTerm questions Name/student ID:_______________ 2 2] LOD 25pts Keloids are scars that proliferate beyond the boundaries of the original injury. Keloids can continue to grow indefinitely and no satisfactory treatment has been identified. Etiological evidence has pointed to a possible genetic predisposition in humans. However, it is unclear what the inheritance patterns of this disease are. Various studies have provided conflicting evidence, supporting an autosomal recessive pattern, an autosomal dominant pattern, or an autosomal dominant with incomplete penetrance. The person pictured had an ear piercing with the resulting keloid scar formation. The pedigree of one family is shown below with persons known to form keloid scars colored in black.. a]. IN the pedigree above, is this trait segregating as a dominant or recessive trait? Explain your case and how you ruled out other options .
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