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.
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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.
