Question

Question 2 The chemical nitrous acid chemically reacts with cytosine (C) to turn it into uracil (U). Imagine that this occurs and affects one C in a tumor suppressor gene. A. When this cell replicates, what sort of changes, if any, will this chemical change cause in the new strands of DNA? Explain in three sentences or fewer. B. Give one way this chemical change could promote cancer. Explain in two sentences or fewer. Question 3 When an embryo is only 2 cells large, one of the 2 cells divides and acquires a cancer-promoting mutation in one allele of the gene p53. As the embryo develops, one of the tissues that the mutated cell gives rise to are all the cells that create sperm. When the person grows up, he also acquires a cancer promoting mutation in one allele of the gene KRAS in his colon. He then fathers a biological child. After he has children, he acquires more mutations and develops colon cancer. A. What is the probability that the child inherited his mutation in p53? Explain in three sentences or fewer B. What is the probability that the child inherited his mutation in KRAS? Explain in three sentences or fewer.

Answer 1

2

A. Uracil pairs with Adenine. So the new strand formed will have Adenine pairing with Uracil instead of Cytosine pairing with Guanine. So the change causes mutation in the DNA.

B. Tumor suppressor gene will not allow tumor formation. When mutation occurs in this gene, it may lead to the development of cancerous tumors.

3.

A. Because the mutation occurred in sperm producing cells of the body, some sperms will carry the mutation. There is probability of 50% that the sperm will have the mutated allele. Because in the father only one mutated allele is present.

B. KRAS mutation occurred in colon cells. This mutated allele is not carried to the sperm as it did not occur in germplasm or sperm producing cells.