ge 9. Figure 7 below illustrates a chromosome nondisjunction event that can some
ID: 254742 • Letter: G
Question
ge 9. Figure 7 below illustrates a chromosome nondisjunction event that can sometimes mistakenly occur during meiosis. Such an event related to human chromosome 21 is responsible for Down syndromeInviduals with Down syndrome have three copies of chromosome 21 instead of the usual two copies. a. Based on what is shown in Figure 7 paternal homolog of chromosome 21 what goes wrong when chromosome nondisjunction occurs? Thinking of the cellular structure responsible for division of chromosomes, hypothesize what causes a nondisjunction event to occur diplold germ-cell precursor of chromosome 21 MEIOTIC DIVISION AND MEIOTIC DIvISION Based on what is shown in Figure 7, what do you think it means for a cell (e.g. a gamete) to be aneuploid? (Hint: think of the terms haploid & diploid). b. aneuploid gametes with 2 copies of chromosome21 gametes without a copy of chromosome 21 Figure 7. Chromsosome nondisjunction and the generation of aneuploid gametes Copyright 2013 from Essential Cell Biology, 4th Edition by Alberts et al. Reproduced by permission of Garland Science/Taylor & Francis LLC. (Figure 19-14) c. Why do individuals with Down syndrome have three copies of chromosome 21? (Only two are show in Figure 7-where does the third come from?)Explanation / Answer
9.
A. In nondisjunction chromosomes are not segregated properly. Nondisjunction causes irregular gemetes with different amount of genetic material. One gemete carries less and one contain more genetic material.
B. Nondisjunction produce two type of gemetes one containing two copy of a chromosome and other 0 copy of a chromosome out of homologous pair. It will produce gemetes are haploid but they contain one more and one less than genome. e.g. n-1/n+1.
C. In Down syndrome chromosome 21 have 3 copies and are trisomic. Due to fertilization of n+1 gamete wit normal n gamete.
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