Home / IB DP Biology- D2.2 Gene expression-IB Style Questions For HL Paper 1A

IB DP Biology- D2.2 Gene expression-IB Style Questions For HL Paper 1A -New Syllabus

IBDP Biology HL Paper 1 -All Chapters

Question

Researchers studying twins measured methylation levels of amino acids associated with chromosome 2. Twin 1 showed significantly and consistently higher methylation than twin 2. Which explanation best accounts for this observation?

A.  Modification to the histone of twin 1
B.  Removal of the histone from the chromosome in twin 2
C.  The DNA base sequence of twin 1 was altered
D.  Cytosines in promoters of twin 2 are more methylated than in twin 1
▶️ Answer/Explanation
Higher methylation of amino acids on chromosome-associated proteins refers to histone tail methylation. This is a post-translational modification of histones, not a change in DNA sequence or promoter cytosine methylation of the other twin.
✅ Answer: (A)

Question

What is a consequence of nucleases binding to mRNA?

(A) Transcription stops.
(B) mRNA binds to ribosomes.
(C) More mRNA is synthesized.
(D) mRNA cannot be translated again.
▶️ Answer/Explanation

Correct Answer: \( \boxed{\mathbf{D}} \)

Nucleases degrade mRNA molecules. Once an mRNA molecule is broken down, it can no longer bind to ribosomes for translation, so it cannot be translated again into a protein.

Question

What is consistently located at the same loci on homologous chromosomes?

A. Alleles with the same function

B. Alleles with identical base sequences

C. Genes with identical base pairs

D. Genes with the same mutations

▶️Answer/Explanation

Answer: A. Alleles with the same function

Explanation:

 

  • Homologous chromosomes have genes at the same loci but may carry different alleles of those genes.
  • These alleles may have different base sequences but usually code for proteins with the same function (even if one allele is mutated).
  • So, while alleles can differ, they generally perform the same biological function at the same loci on homologous chromosomes.

Why other options are incorrect:

B. Alleles with identical base sequences: Alleles can have slight sequence variations.

C. Genes with identical base pairs: Alleles can differ in base pairs due to mutations.

D. Genes with the same mutations: Not all homologous chromosomes carry the same mutation.

 
More DP Biology HL Paper 1- Questions..
Scroll to Top