Past paper: Selection and evolution

Question 1

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1. a) What is meant by the term ‘species’

Answer 1

Species: a group of organisms with similar morphology and physiology, which can breed together to produce fertile offspring and which is reproductively isolated from other species.

Question 2

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1. b) type of isolation

Answer 2

geographical isolation

Question 3

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1. c) Explain how the process of isolation occured in the greenish warbler populations

Answer 3

1. No breeding between population
2. Gene mutation occurs
3. Different selection pressures resulting in different alleles being selected for.
4. Over time, they do not recognise song, and interbreed cannot be happened.
5. Speciation happens like this, when 2 populations are separated by a geographical barrier is known allopatric speciation.

Question 4

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4. a) 2 features adapt for wind pollination

Answer 4

• Anthers large to produce large quantities of pollen

- Anthers outside to allow wind to carry pollen away

Question 5

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4. b) How resistance could have evolved

Answer 5

1. Gene mutation occurs which give corn borer the selective advantage -> more likely to survive.
2. Mutated gene passed onto the next generation.
3. Increased frequency of allele for mutation.
4. they are likely to breed

Question 6

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1. a) ii) Explain how disruptive selection has been maintained in this species of seahorse

Answer 6

• Mate selected by sizes
• Few intermediates mate
• intermediates selected against / extremes selected for
• Alleles for extreme phenotypes (more likely to be) passed on

Question 7

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1. a) iii) (iii) State the term given to the type of selection where variation in a characteristic is maintained in its existing form over time.

Answer 7

Stabilising selection

Question 8

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1. b) Suggest how these two different species of Hippocampus could have arisen.

Answer 8

• Allopatric speciation
• Different selection pressures
• Eventually no longer interbreed

Question 9

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8. (a) Explain how the change from an extensive lake system to just a few pools could have resulted in the evolution of four new species of desert pupfish.

Answer 9

(a) 1. allopatric speciation;
2. fish populations isolated;
3. geographical / physical / land, barrier;
4. no, breeding / allele flow / gene flow, between populations;
5. mutations occur;
6. different selection pressures / different (environmental) conditions;
7. advantageous alleles selected for / advantageous alleles passed on;
8. change in, allele frequency / gene pool;
9. (can result in) different chromosome numbers;
10. genetic drift;
11. ultimately, reproductively isolated / cannot interbreed;

Question 10

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8. b) State how environmental factors can act as stabilising forces of natural selection in an isolated pool, after the initial evolution of a new species of desert pupfish.

Answer 10

1. conditions remain the same within the pool;
2. best adapted fish (to conditions in pool) survive;
3. extreme phenotypes, selected against / do not survive;

Question 11

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8. c) Suggest what may happen to the desert pupfish if water levels rise and the pools once more form an extensive lake system.

Answer 11

1. numbers of all species increase initially;
2. due to more, breeding space / food;
3. competition between (four) species;
4. (possible) reduction in numbers within, some / all, species;
5. not all species (may) survive;
6. different species, restricted to different areas / occupy different niches;
7. interbreeding / hybridisation;
8. AVP; e.g. ref. new selection pressure

Question 12

1. a) Explain the role of isolating mechanisms in the evolution of new species (8)

Answer 12

• Allopatric speciation, geographical isolation (barrier)
• Sympatric speciation, meiosis problems can occur through polyploidy.
• Isolated populations can only breed amongst themselves.
• No gene mixing, different selection pressures operate
• Natural selection
• Change in allele frequencies
• Different GENE POOL
• over time, differences prevent interbreeding
• Reproductive isolated

Question 13

1. b) Describe and explain, using an example, the process of artificial selection (7)

Answer 13

• Humans purposefully apply pressures to populations
• Parents with desirable feature
• Crossed together
• Select offspring with desirable feature
• Repeat over many generations
• Increase in frequency of desired alleles
• Inbreeding Depression: the plants in each generation become progressively smaller and weaker. Loss of hybrid vigour.

Question 14

2. a) Describe the role of natural selection in evolution

Answer 14

• Individuals in population have great reproductive potential.
• Numbers in population remain roughly constant
• Many fail to survive, do not reproduce due to environmental factors
• Variation in members of population
• Those best adapted survive -> pass on elleles
• Genetic variation leads to change in phenotype
• Overtime, produces evolutionary change
• New species arise from existing ones

Question 15

2. b) Explain, using named examples, how mutation can affect phenotype

Answer 15

• Sickle cell
• Change in gene (base) -> different amino acid -> different protein.
• Structural changes in chromosomes
• Change in number of chromosomes
• Change in sets of chromosomes (polyploidy)

Question 16

3. a) Explain why variation is important in natural selection

Answer 16

• Continuous/ discontinuous variation
• Genetic variation
• Variation in phenotypes (characterictics) can be due to interaction of genotype and environment
• Characteristic that influences survival
• Those with favourable characteristics survive and pass on their alleles to offspring.
• Those with disadvantageous characteristics die

Question 17

4. Discuss the link between the frequency of sickle cell anaemia and the number of cases
   of malaria.

Answer 17

• Frequency of sickle cell anaemia is highest in areas where malaria is common because sickle cell anaemia RBC cannot carry oxgygen very well -> doesn’t suffer from malaria
• Homozygous HbsHbs have sickle cell anaemia and may die
• HbaHba have normal red blood cells
• Heterozygotes have sickle cell trait and RBC not severely affected.
• Malaria parasite (Plasmodium) affects RBC
• Sickly cell trait people less likely to suffer from severe effects of malaria -> have selective advantage.
• Pass on normal alleles as well as sickle cell anaemia
• Sickle cell allele is maintained within population
• Malaria selects against homozygous HbAHbA
• Sickle cell anaemia selects against homozygous HbSHbS

Question 18

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2. (a) Explain how variation and natural selection may have brought about the evolution of the
woolly mammoth from the steppe mammoth.

Answer 18

1. individuals varied (in their phenotypes) ;
2. (phenotypic variation) caused by, genetic variation / mutation ;
3. change in, selection pressure / environmental conditions ;
4. idea that variation increases the chance of some individuals surviving / AW ;
5. named adaptation explained ; e.g. better insulation / smaller surface area to volume
6. survivors breed ;
7. passed on alleles to offspring ;
8. changed allele frequency (in population) ;

Question 19

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2. b) The results suggested that, when compared with Asian elephants:
• there was only one different amino acid in the woolly mammoth’s α chains
• there were three different amino acids in the woolly mammoth’s β chains.

Explain the likely effect of these differences on a molecule of mammoth haemoglobin

Answer 19

(b) 1. differences in, primary structure / sequence of amino acids / polypeptide ;
2. provides different, side chains / R groups ;
3. change in, tertiary structure / 3D shape ;
4. effect on quaternary structure ;
5. greater effect on β chain ;
6. change in properties ; A function

Question 20

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2. c) i) Suggest why it is advantageous for Arctic mammals to have haemoglobin whose affinity for oxygen is only slightly affected by changes in temperature.

Answer 20

(c) (i) 1. still able to offload oxygen (in cold temperatures) ;
2. surface tissues colder than, core / body, temperature ;
3. so can maintain oxygen supply to surface tissues ;

Question 21

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2. c) ii) Explain whether or not Fig. 2.1 provides evidence that woolly mammoth haemoglobin is better adapted for a cold climate than Asian elephant haemoglobin.

Answer 21

(ii) 1. no / tiny, difference in effect of temperature on haemoglobin alone ;
2. so no evidence (woolly mammoth haemoglobin) better adapted ;
3. greater reduction in effect of temperature on haemoglobin with red cell effector in
woolly mammoth ; ora
4. (so) woolly mammoth haemoglobin (with red cell effector) better adapted to cold ;
5. ref. change to oxygen binding sites ;
6. so can offload oxygen at low temperatures ;

Question 22

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2. (a) Outline the advantages of captive breeding programmes such as CCRP.

Answer 22

(a) 1 supplied with food ;
2 monitor health of the, mother/offspring ;
3 (sperm/eggs) stored/frozen ; A sperm bank
4 artificial insemination/in vitro fertilisation ; A AI/IVF
5 ref. to cloning/ surrogacy/fostering (of young) ;
6 fertilised eggs incubated artificially ;
7 transfer of breeding partners between zoos ;
8 maintenance of records ;
9 maintains genetic diversity ;
10 protection from, predators/ shooting/disease ;

Question 23

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(b) Suggest why animals in captive breeding programmes may not always breed successfully.

Answer 23

(b) 1 no longer living in natural habitat ;
2 stress ;
3 behavioural changes ;
4 idea of disruption to normal reproductive cycles ;
5 reject mate ;

Question 24

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(c) When animals that have been bred in captivity are released, their survival rate is low.
Suggest two reasons why many of these animals are unable to survive in the wild.

Answer 24

(c) 1 may find difficulty in moving around (due to previously been captive) ;
2 idea of difficulty obtaining food/short of food/outcompeted for food ;
3 difficulty integrating with others of members of their species ;
4 disease ;
5 idea of lack of survival skills ; A lack of fear of, humans/predators

Question 25

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4. b) (ii) Research has also shown that, in a population of collared lizards with varying leg lengths,
those with longer hind legs are able to run faster.
With reference to the results shown in Fig. 4.3, explain how, over time, this could lead to
a change in the mean hind leg length in a population of collared lizards.

Answer 25

(ii) lizards with longer (hind) legs will tend to have more offspring ;
so will have a greater chance of passing on their alleles ;
(over time) the frequency of alleles (for long hind leg) will increase ;
so mean hind leg length will increase ;
directional selection ;

Question 26

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4. (c) Small islands often contain species of lizards that are not found on other islands or on the
mainland.
Explain how a population of collared lizards that became isolated on an island could evolve to
form a new species.

Answer 26

(c) no, breeding/ allele flow/ gene flow, between (lizard) populations ;
different selection pressures / different (environmental) conditions ;
mutations occur ;
advantageous alleles, selected for/ passed on ;
change in, allele frequency /gene pool ;
genetic drift ;
(eventually) unable to interbreed ;
allopatric speciation ;

Question 27

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5. (a) In mice with the genotype A1A1, the amino acid at position 64 in the α-polypeptide chain is
aspartic acid. In mice with the genotype A0A0, the amino acid at this position is glycine.
Suggest how the change from aspartic acid to glycine in the α-polypeptide chain could have
been brought about.

Answer 27

(a) random/ spontaneous ;
mutation ;
base/nucleotide/triplet, change/ substitution ; R addition/ deletion

Question 28

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5. b) (i) Describe the effect of altitude on the frequency of the haemoglobin alleles in these
populations of deer mice.

Answer 28

(b) (i) as altitude increases frequency of A0
increases ; ora for A1
A0 more frequent at high altitudes / A1
more frequent at low altitudes /
intermediate frequency of either allele at intermediate altitude ;

Question 29

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5. b) (ii) The partial pressure of oxygen is relatively low at high altitudes. Haemoglobin containing
glycine at position 64 in the α-polypeptide chain has a higher affinity for oxygen than
haemoglobin with aspartic acid at this position.
Suggest how natural selection could account for the difference in allele frequency in deer
mice living at high altitudes and low altitudes.

Answer 29

(ii) idea of (pre-existing) genetic variation in deer mouse population ;
at high altitude mice with, glycine/A0
, more likely to survive/ have selective
advantage ; ora
mice (with A0 ) reproduce (at high altitude) ; ora
and pass on the A0
allele ; ora
partial pressure/ concentration, of O2 acts as a selection pressure ;
ref. to disadvantage of haemoglobin with very high affinity at low altitude ;
as less able to unload oxygen (in respiring tissues)