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Question 23M.3.HL.TZ1.13

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Date May 2023 Marks available [Maximum mark: 5] Reference code 23M.3.HL.TZ1.13
Level HL Paper 3 Time zone TZ1
Command term Describe, State, Suggest Question number 13 Adapted from N/A
13.
[Maximum mark: 5]
23M.3.HL.TZ1.13

The data shows the amino acids found in a section of histone protein from various mammals. The lighter columns show differences in the amino acid sequence between the mammals.

[Source: Shafee, T., 2014. Histone Alignment. [online] Available at: https://commons.wikimedia.org/w/index.php?curid=37188728.
Public domain.]
(a)

State the name of the software which could be used to obtain the data.

[1]

Markscheme

BLAST(p) / Clustal W / T-Coffee;

Examiners report

Many were able to correctly identify BLAST as the software used to find the amino acid sequence in a protein.

(b)

Suggest how the nucleotide sequence for this section of the protein may show more differences than the amino acid sequence.

[1]

Markscheme

the genetic code is degenerate/each amino acid has more than one codon;

Examiners report

Many also were able to get the mark here, understanding that the genetic code is degenerate.

(c)

Describe with reference to the data how multiple sequence alignment can be used to trace evolutionary relationships between humans and other species.

[3]

Markscheme
  1. evolved from a common ancestor with a given amino acid sequence (for histone protein);
    OR
    (accumulation of) mutations over time may lead to new species/ evolution;
  2. Least number of differences in (amino acid) sequence shows closer relationship;
  3. human sequence in the data is more similar to the chimp than other species/mouse/rat/cow;
  4. humans and chimp have a more recent common ancestor;

b. Accept vice versa.

c. Accept vice versa.

Examiners report

This was poorly answered by most candidates as they did not reference the data as asked in the question and were not able to describe clearly how multiple sequence alignment can be used to trace evolutionary relationships.