IB Biology HL D1.3 Mutation and gene editing questions

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Question 1

Paper 2Medium16 marks

A gene in a population encodes part of a polypeptide. The table shows the coding-strand DNA sequence from a reference individual and three variants found in other individuals. The mRNA codons and their amino acids relevant to these sequences are also shown.

SequenceCoding-strand DNA, 5′→3′
ReferenceGAA CCT TGG
PGAG CCT TGG
QGAA CAT TGG
RGAA CCT TGC
mRNA codonAmino acid
GAAglutamic acid
GAGglutamic acid
CCUproline
CAUhistidine
UGGtryptophan
UGCcysteine
(a)

For P, Q and R, state the codon and nucleotide substitution. Explain why these differences are SNPs.

[4]
(b)

For each variant, state the amino acid encoded at the changed codon and whether this amino acid differs from that in the reference sequence.

[6]
(c)

Explain why the substitution in P does not change the amino acid.

[3]
(d)

A student concludes that variants Q and R must produce a different phenotype from the reference individuals. Evaluate this conclusion using the information given.

[3]

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