Question
Which processes are involved in the development of cancer?
Mutations occur in oncogenes.
Oncogenes prevent cancer.
Oncogenes affect cell cycle regulatory proteins.
I and II only
I and III only
II and III only
I, II and III
Answer/Explanation
Answer: A. I and III only
Explanation:
What is Cancer and How Does It Develop?
Cancer is the uncontrolled division of abnormal cells in the body. It usually happens because of mutations in genes that control the cell cycle. Two key gene types are involved:
- Oncogenes – mutated forms of normal genes (proto-oncogenes) that promote cell division. When these genes are overactive, they can lead to cancer.
- Tumor suppressor genes – normally help slow down cell division or cause damaged cells to die. If these are mutated and stop working, cancer can also result.
Evaluating Each Statement:
A. I and II only – Incorrect
- Statement I is correct (mutations in oncogenes can cause cancer), but statement II is false. Oncogenes promote cancer, they do not prevent it.
B. I and III only – Correct
- Statement I is true.
- Statement III is true: oncogenes can affect proteins that regulate the cell cycle, pushing cells to divide uncontrollably.
C. II and III only – Incorrect
- Statement II is false (oncogenes don’t prevent cancer), so this choice cannot be correct.
D. I, II and III – Incorrect
Statement II is incorrect, so including it makes this answer wrong.
In a person who is heterozygous for sickle-cell anemia, where is the mutation found?
A. In every gamete produced
B. Only in gametes carrying an X chromosome
C. In all brain cells
D. In blood plasma
Answer/Explanation
Answer: A. In every gamete produced
Explanation:
What Does It Mean to Be Heterozygous for Sickle-Cell Anemia?
Sickle-cell anemia is caused by a mutation in the gene that codes for hemoglobin, found on chromosome 11. A heterozygous person has one normal allele and one mutated allele. This mutation is present in all cells because it is inherited at conception, when the zygote forms.
Evaluating Each Option:
A. In every gamete produced – Correct
Half of the gametes will carry the mutated allele, because meiosis separates the two alleles into different gametes. Every gamete has one allele — either the normal or the mutated one.
B. Only in gametes carrying an X chromosome – Incorrect
The sickle-cell gene is not on the X chromosome; it is on chromosome 11, an autosome.
C. In all brain cells – Correct, but not the best answer
The mutation is indeed present in all cells, including brain cells. However, the question asks specifically about gametes, making option A more directly relevant.
D. In blood plasma – Incorrect
Plasma is the liquid part of blood and does not contain DNA. The mutation is in cells, not in the plasma.
One type of gene mutation involves a base substitution.
What are the consequences of the base substitutions in the two new sequences of DNA?
A. Both are mutations that would result in different polypeptides.
B. Sequence 2 would result in a changed polypeptide but sequence 1 would not.
C. All three DNA sequences would translate into the same polypeptide.
D. Only the original DNA and sequence 2 would translate into the same polypeptide.
Answer/Explanation
Answer: D. Only the original DNA and sequence 2 would translate into the same polypeptide.
Explanation:
What is a Base Substitution Mutation?
A base substitution mutation is when a single nitrogen base in DNA is replaced by a different base. This can lead to three possible effects:
- Silent mutation: No change in the resulting amino acid.
- Missense mutation: One amino acid in the protein changes.
- Nonsense mutation: The change introduces a stop codon, halting translation early.
To determine the effect, we must:
- Identify the mutated codon.
- Transcribe the DNA to mRNA.
- Translate the codon into its amino acid using the genetic code.
- Compare the resulting polypeptides.
Evaluating Each Option:
A. Incorrect
Both sequences have a base substitution, but only Sequence 1 changes the amino acid (glutamic acid to valine). Sequence 2 changes the codon from GAG to GAA — both still code for glutamic acid. So, both do not cause different polypeptides.
B. Incorrect
This option reverses the actual outcome. It says Sequence 2 causes a change, but it does not GAA still codes for glutamic acid. It is Sequence 1 that changes glutamic acid to valine.
C. Incorrect
Sequence 1 causes a change in the amino acid. So not all three sequences produce the same polypeptide.
D. Correct
The original DNA and Sequence 2 both result in the same amino acid sequence (glutamic acid is still made). Sequence 1, however, results in a different amino acid (valine), changing the polypeptide.