4.4 Genetic diversity and adaptation practise questions

Question 1

The fruit fly is a species of small insect.
The fruit fly has a gene that codes for an enzyme called alcohol dehydrogenase
(AD). AD catalyses the breakdown of alcohol when alcohol is in the insects’ food.
The gene coding for AD has two alleles, ADF and ADS.
(a) The enzyme encoded by the ADF allele catalyses the breakdown of alcohol
faster
than the enzyme encoded by the ADS allele. Suggest why

Answer 1

) 1. Different primary structure/amino acid sequence;
2. Different tertiary structure/shape of active site;
3. Enzyme-substrate complexes more likely (with enzyme from ADF
allele);

Question 2

A scientist took a random sample of adult fruit flies from a population. He
measured the frequency of the ADF allele in this sample (generation 0). He then:
* selected 100 of these insects at random and kept them in a container
* fed the insects food containing alcohol
* let the insects reproduce
* repeated these steps for 45 generations of fruit fly reproduction.
The scientist measured the frequency of the ADF allele in the 45th generation.
(b) Suggest why the scientist took his sample from the population at random

Answer 2

Avoids bias
OR
Results (likely to be) reliable/repeatable;

Question 3

Alcohol is toxic to fruit flies. Suggest and explain why the frequency of the
ADF allele changed during the 45 generations.

Answer 3

1. Flies with ADF/allele have selective advantage (in presence of
   alcohol);
   Accept converse for ADS
   Accept description of selective advantage
2. So insects (with ADF more likely to) reproduce;
3. Pass on ADF (allele/gene);
4. (So) allele frequency increases;

Question 4

What type of selection were the scientists modelling in this investigation by
putting back only the largest or only the smallest fish in Tank A and Tank
C? Give a reason why.
Type of selection
Reason

Answer 4

Type of selection
1. Directional;
Reason:
2. One extreme selected/removed/favoured/chosen
OR
One extreme allowed to breed;

Question 5

Sea fishing is regulated in law. The size of the mesh used in some fishing
nets is controlled so that small fish can escape but large fish are captured.
This regulation is designed to protect populations of wild fish.
Using all the information in this question, evaluate whether the scientists’
investigation supports the use of these types of nets in sea fishing.

Answer 5

1. (Sea) fishing reduces (mean) mass of fish;
2. Because large fish removed
   OR
   Because small fish escape/put back
   OR
   Because fishing (model) like Tank C;
   But
3. Information from (only) one species
   OR
   Sea fishing catches other/different (types of) species;
4. No statistical test;
5. Size of tank may affect fish growth;
6. Fish in tanks are all same age/sea fish not all the same age;
7. No measure of number of fish (removed)/ only measured mean
   mass
   OR
   No measure of (total) yield of fish
   OR
   No measure of reproductive success of fish;
8. Removal of 90% of population is unlikely to be replicated in the
   sea fishing;
9. Sea fish do not have life cycle of one year
   OR
   Sea fish do not reproduce all at the same time;

Question 6

A student used a dilution series to investigate the number of cells present
in a liquid culture of bacteria.
Describe how he made a 1 in 10 dilution and then used this to make a 1 in
1000 dilution of the original liquid culture of bacteria.

Answer 6

1. Add 1 part (bacteria) culture to 9 parts (sterile) liquid (to make 10–1
   dilution);
   Accept water / nutrient / broth for liquid
2. Mix (well);
   Accept stir
3. Repeat using 9 parts fresh (sterile) liquid and 1 part of 10–1 and 10–2
   dilutions to make 10–3 dilution;
   OR
   Add 1 part 10–1 (suspension) to 99 parts (sterile) liquid (to make 10–3
   dilution);

Question 7

The student looked at cells in the 1 in 10 dilution during his preliminary
work. He decided not to use this dilution to determine the number of cells
in the undiluted liquid culture.
Suggest an explanation for the student’s decision.

Answer 7

. Count unlikely to be accurate / repeatable / reproducible / reliable;
2. Because too many cells;
OR
Because cells overlapping / not spread out;

Question 8

Suggest and explain one reason why bacteria resistant to tetracycline are
more common than bacteria resistant to streptomycin in these farm
animals

Answer 8

1. Tetracycline used more often / in higher doses;
2. Resistant bacteria more likely to (survive and reproduce and) pass on
   allele/gene for (tetracycline) resistance;
   OR
3. More / higher frequency of mutations (for tetracycline resistance);
   Reject reference to mutation being caused by use
   of antibiotic
4. (so) gene passed on to more bacteria;
   OR
5. Tetracycline used over longer time period;
6. More time for (chance) mutation to occur / for selection to occur;

Question 9

In recent years, these farm animals have not been given tetracycline in
their food. Despite this, the percentage of bacteria resistant to tetracycline
has remained constant.
Suggest one reason why.

Answer 9

No selection against resistant bacteria / resistance gene/allele;
OR
Bacteria pass on (resistance) gene / allele when they reproduce;
OR
Bacteria resistant to tetracycline are passed on from one generation of
farm animals to the next (probably via faeces);
OR
Environment does not change, so stabilising selection occurs;

Question 10

Lactose is the main sugar in milk and is hydrolysed by the enzyme lactase.
Lactase is essential to newborn mammals as milk is their only source of food.
Most mammals stop producing lactase when they start feeding on other food
sources. Humans are an exception to this because some continue to produce
lactase as adults. The ability to continue producing lactase is known as lactase
persistence (LP) and is controlled by a dominant allele. A number of hypotheses
based on different selection pressures have been put forward to explain LP in
humans.
(a) One hypothesis for LP in humans suggests that the selective pressure was
related to some human populations farming cattle as a source of milk.
Describe how farming cattle as a source of milk could have led to an
increase in LP.

Answer 10

1. LP due to mutation
   OR
   Allele due to mutation;
   Reject mutation caused by drinking milk.
   Reject (LP) gene
2. Milk provides named nutrient;
   Accept any correct named nutrient e.g. glucose,
   galactose, protein
   Ignore ‘sugar’ ‘lactose’ as named nutrient
3. Individuals with LP more likely to survive and reproduce
   OR
   Individuals with advantageous allele more likely to survive and
   reproduce;
   Reject (LP) gene
   Accept ‘individuals who produce lactase’ for ‘LP
   individuals’
   Accept ‘pass on allele/LP/characteristic’ for
   reproduce.
4. Directional selection;
5. Frequency of allele increases (in the offspring/next generation);

Question 11

Use the information provided to explain why the number of people showing
LP would rapidly increase once selection for this condition had been
established.

Answer 11

1. Dominant allele;
2. (Always) expressed/shown (when present in phenotype/offspring)
   OR
   Expressed when only one (dominant allele) present;

Question 12

Lactase persistence is caused by a mutation in DNA. This mutation does
not occur in the gene coding for lactase.
Suggest and explain how this mutation causes LP.

Answer 12

1. Mutation in promoter (DNA/gene) for transcription factor
   OR
   Mutation in promoter (region/DNA) for the gene
   OR
   Mutation in gene for transcription factor;
   Accept mutation in an epistatic gene
2. Lactase gene continues to be transcribed/active;