Question

1. A 28-year-old male graduate student was born with an inherited predisposition to colon cancer due to a mutation in a DNA repair gene called MLH1. He has recently been diagnosed with colon cancer.

a. At the cellular and genetic level, was he born with colon cancer?

b. Was he born with a predisposition to colon cancer?

c. At birth, were cells in his colon genetically identical to cells in his liver?

d. Now that he has colon cancer, are his cancer cells genetically identical to his normal colon cells? Explain your answers.

2. People like Lorene Ahern (Chpt 10) have inherited a mutated version of BRCA1.

a. Why does this mutation pose a problem?

b. Why are these people at high risk of developing breast cancer when they still have a functional BRCA1 allele?

c. Describe how the protein encoded by normal BRCA1 compares to that encoded by mutant alleles of BRCA1.

Answer 1

Question1:

(a) The answer is no. He was not born with colorectal cancer. He has a mutation in the DNA repair gene, which means he can acquire cancer because of the inability of the cells to repair the damage caused. So at cellular and genetic level he's not born with cancer. Cnacer is a gradual process.

(b) Answer is yes. The boy is definitely predisposed to cancer. Usually people with mutation in MLH1gene often develop colorectal cancer in the later years of life. There's a very logical reason behind this. Cancer is a gradual process. If a person has a mutation in a crucial gene like DNA repair gene, the chnaces of him getting cancer are normal, especially in the organs that continuously replenish. The probablity of a cell to turn malignant with a mutation in organs that have continuous proliferation of cell like colon, is high. So yes the boy was predisposed to this condition.

(c) All the cells inside any normal person's body are genetically identical. Due to differential expression of genes, they tend to become different cells, otherwise the genes are same in each and every cell. So yes, the boy had colon cell genetically identical to liver cell. Remeber they're only genetically identiclem i.e, the mutation is present in liver cells as well.

(d) The answer is clearly no. Once a person develops cancer, it is because of the fact that the cells have acquired multiple mutation. Cancer occurs step by step. So the cancerous cells are very different from normal cells genetically as well as phenotypically. The boy's colon cells that are malignant are not similar to normal colon cells genetically because they might have acquire many mutations to become malignant cells.

(We're supposed to answer only first four questions, so I request you to repost the remaining questions)