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Date	May 2017	Marks available	1	Reference code	17M.2.SL.TZ2.4
Level	Standard level	Paper	Paper 2	Time zone	Time zone 2
Command term	State	Question number	4	Adapted from	N/A

Question

Mutations are the ultimate source of genetic variation and are essential to evolution.

Lice are wingless insects that belong to the phylum arthropoda.

State one type of environmental factor that may increase the mutation rate of a gene.

[1]

a.i.

Identify one type of gene mutation.

[1]

a.ii.

State two characteristics that identify lice as members of the arthropoda.

[2]

Some lice live in human hair and feed on blood. Shampoos that kill lice have been available for many years but some lice are now resistant to those shampoos. Two possible hypotheses are:

Discuss which hypothesis is a better explanation of the theory of evolution by natural selection.

[3]

b.ii.

Markscheme

a. radiation

b. chemical mutagens/carcinogens/papilloma virus/cigarette smoke

a.i.

base substitution/insertion/deletion/frameshift

a.ii.

a. jointed appendages

b. «chitinous» exoskeleton

c. segmented body
OR
bilateral symmetry
OR
mouth AND anus
OR
paired appendages

a. «scientists would accept» hypothesis A as the better one as mutations are random

b. scientists would reject hypothesis B because characteristics acquired during the lifetime of the individual being inherited is Lamarckian/not part of the evolution by natural selection theory/not all mutations are heritable

c. «the resistance» mutation would be present in the population initially and not caused by the shampoo «as hypothesis B states»

d. both hypotheses include variation in the population of lice «resistant and non-resistant»

e. variation is necessary for natural selection to occur

f. frequency of the best adapted increases and these individuals reproduce/pass on resistance to their offspring, so the resistant population increases «so hypothesis A is better»

OWTTE can be used for any of the answers in this part.

b.ii.