a. breaks at or near the centromeres of two acrocentric chromosomes b. breaks at
ID: 68375 • Letter: A
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a. breaks at or near the centromeres of two acrocentric chromosomes b. breaks at or near the centromeres of two metacentric chromosomes c. breaks at or near the centromeres of one acrocentric and one metacentric chromo d. breaks in a large and a small chromosome e. transposable elements ngle cross over event within gene C of the chromatids below will result in which of the following'? 96. A si ABCD and A CB D a. AB BD and AD b. A C D and A B B D c. A B C D and A C B D d. A B C D and A B C D e A B C B D and A C D 97. Familial Down's syndrome results from a. trisomy of chromosome 21 as a result of meiotic nondisju of chromosome 21 as a result of meiotic nondisjunction b. loss of the small arm of chromosome 21 following a Robertsonian translo cation in somatic tissue c. production of a large metacentric chromosome containing the long arm of chromosome 21 in germ tissue d. fertilization events between 2 parents with trisomy 21 ll of the above can cause familial Down's syndrome 98. Normal cells avoid becoming cancerous when their DNA is damaged by a. preventing cell division b. inducing DNA synthesis c. activating RB d. activating p53 e. a and d 99. The gene product RB is associated with: a. controlling when the cell enters S phase b. preventing S phase when DNA damage is present c. nitiating apoptosis d. spindle fibre formation e. all of the above 100. When DNA damage cannot be repaired, cells normally enter apoptosis to prevent mutations fro being perpetuated. This is induced by a. accumulation of RB b. accumulation of p53 c. telomerase d. necrosis e. senescence Page 19 of 20Explanation / Answer
97). e. All of the above can cause familial Down's syndrome.
Individuals with Down syndrome carry three copies of chromosome 21 (trisomy). During meiosis, instead of the third copy being separate, “translocation” of this copy may occur and attached to another chromosome (Roberstonian translocation). In Down’s syndrome, usually translocation of 14/21 chromosomes occur. Hence, the chromosome number would be still 46 but, the chromosome 14 appears longer than the normal.
98). e. a and d.
p53 is a tumor suppressor gene. Mutations during cell division are detected by check points, the cell cannot divide until it passes through the check point. Activation of tumor suppressor genes prevent the cells turning to cancerous.
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