1. Cyclophosphamide forms crosslinks between the two strands of DNA in a chromos
ID: 66187 • Letter: 1
Question
1. Cyclophosphamide forms crosslinks between the two strands of DNA in a chromosome. How would this be effective in chemotherapy?
A. It would block splicing
B. It would block DNA replication
C. It would activate oncogenes
D. It would inactivate tumor suppressors
E. It would block metaphase
2. Which of the following occurs in meiosis I ?
A. All chromosomes duplicate
B. Homologous chromosomes randomly orient themselves on the metaphase plate, called independent assortment
C. The dupicated sister chromatids separate
D. The original cell divides into four diploid cells
E. none of the above
Can you please briefly expain why?
Explanation / Answer
Q1). B. It would block DNA replication
The cyclophosphamide is an alkylating agents and bipolar, i.e. they contain two groups capable of reacting with DNA. They can thus form bridges between a single strand or two separate strands of DNA, interfering with the action of the enzymes involved in DNA replication.
Q2). B. Homologous chromosomes randomly orient themselves on the metaphase plate, called independent assortment
In Meiosis I members of homologous pairs separate during anaphase. The separation of each pair is random with respect to all the other pairs. For each pair there is a maternal and a paternal chromosome which came from the mother and father respectively. There is no mechanism to cause maternal or paternal chromosomes to either associate with or repel one another. Therefore the orientation of each chromosome pairs is random with respect to other chromosome pairs. This is necessary for the independent assortment of genes, an important principle of genetics. It also allows for gametes, and thus offspring, to be much more genetically variable than they would be if all the paternal and maternal chromosomes were inherited as a unit.
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