Genetics, Populations, Evolution & Ecosystems

Question 1

Male fruit flies are more likely than female fruit flies to have white eyes.
Explain why

Answer 1

As they only have 1 X chromosome
They only need 1 recessive allele for it to be expressed
Whereas females need 2 recessive alleles

Question 2

Mutation is one cause of genetic variation in organisms.
Give two other causes of genetic variation

Answer 2

Random fertilisation
Crossing over
Independent segregation

Question 3

A population of this species of plant contained 9% of red-flowered plants.
Use the Hardy–Weinberg equation to calculate the percentage of
pink-flowered plants in this population.
Show your working.

Answer 3

p^2= 0.09 p =0.3
q= 0.7
2pq= 2x0.3x0.7= 0.42
42%

Question 4

In genetic crosses, the observed phenotypic ratios obtained in the offspring
are often not the same as the expected ratios.
Suggest two reasons why.

Answer 4

Small sample size
Fertilisation is random
Epistasis
Autosomal or sex linkage
Lethal genotypes

Question 5

What is meant by the term phenotype?

Answer 5

The expression of an organisms genotype and its interaction with its environment

Question 6

What is meant by codominant alleles?

Answer 6

Both alleles are expressed if they are present in the genotype

Question 7

Suggest how the change in the anticodon of a tRNA leads to Mitochondrial Disease,

Answer 7

Change in tRNA anticodon means different amino acid is inserted in polypeptide
This causes a change in tertiary structure
This protein may be involved in ETC/Krebs cycle so less ATP made

Question 8

It is caused by having only rods and no functional cone cells.
People with complete
achromatopsia have difficulty in seeing detail
Explain why.

Answer 8

Only rods no functional cones.
Many rod cells are connected to a single neuron
So they send a single impulse to the brain

Question 9

What is a gene pool?

Answer 9

All of the alleles present in a population

Question 10

They observed each female for 10 minutes and recorded which male they were
attracted towards. They repeated this with 45 large-brained females and 45
small-brained females.
(a) Suggest three possible limitations of this investigation.

Answer 10

Transparent barrier may prevent normal courtship
Only recorded for 10 minutes may not be long enough for females to decide
Laboratory raised guppies may not behave the same as wild ones
Do not know if guppies have been used in previous experiments

Question 11

Guppies with large brains are better at identifying predators.
The scientists found that only female guppies with large brains were attracted to
male guppies bright in colour.
(b) Suggest and explain the advantage of this behaviour to the population of
guppies.

Answer 11

Females with large brains will mate with males bright in colour
This means male offspring are more likely to be brightly coloured
So offspring would attract females with larger brains
The population could evolve to have larger brains
So would be better at spotting predators

Question 12

Describe how the behaviour of female guppies could result in sympatric
speciation.

Answer 12

Not geographically isolated
Results in reproductive isolation
As gene pools do not mix
Change in allele frequency
So they can no longer breed to produce fertile offspring

Question 13

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 13

LP allele exists due to random mutation
Milk provides glucose which is useful
Individuals with LP allele are more likely to survive and reproduce
Frequency of allele increases
Directional selection

Question 14

Lord Howe Island in the Tasman Sea possesses two species of palm tree
which have arisen via sympatric speciation. The two species diverged from
each other after the island was formed 6.5 million years ago. The flowering
times of the two species are different.
Using this information, suggest how these two species of palm tree arose
by sympatric speciation.

Answer 14

They are not geographically isolated
They have become reproductively isolated
Mutation results in different flowering times
As they flower at different times, they will only be pollinated with the trees that also flower at this point
This means the gene pools do not cross
Allele frequencies change
Disruptive selection
They are no longer able to breed and produce fertile offspring

Question 15

Suggest and explain two reasons why there is a high frequency of the
E280A mutation in Yaramul (an isolated population)

Answer 15

They are isolated so there is inbreeding
Inherited from a common ancestor

Question 16

Explain why natural selection has not reduced the frequency of the E280A
mutation in the population (Alzheimer’s)

Answer 16

Alzheimer’s symptoms develop late in life
So they will have already reproduced

Question 17

One farmer stated that the increase in the use of Bt crop plants had
caused a mutation in one of the insect species and that this mutation had
spread to other species of insect. Was he correct? Explain your answer

Answer 17

No
Mutations are random
Only environment can effect rate of mutation
Different species cannot interbreed and produce fertile offspring
So the allele cannot pass between species

Question 18

Explain how different subspecies of giraffe may have evolved from a
common ancestor.
Different subspecies have different markings

Answer 18

The population gets separated geographically so there is no flow in alleles between these populations
Different markings exist due to mutation
They face different selection pressures in their environments so giraffes with specific markings are more likely to survive in different environments
The better adapted organisms breed
Allele frequency increases for these markings

Question 19

Biologists compared the mitochondrial DNA of the different subspecies of
giraffe. They used the results from comparing this DNA to conclude that six
of the nine subspecies are separate species.
Suggest how they came to this conclusion

Answer 19

Compare DNA base sequence
Different in 6 species and similar in 3

Question 20

Lake Malawi in East Africa has more species of fish than any other lake in
the world (line 1).
Suggest and explain how this speciation may have occurred

Answer 20

There is variation in the population due to mutation
They undergo allopatric speciation
Different lakes have different environments
There is no gene flow so gene pools remain separate
Different alleles are selected for so allele frequency increases
Eventually they can no longer produce fertile offspring

Question 21

Loss of nutrients into Lake Malawi has resulted in a decrease in some fish
populations (lines 12–13).
Explain why

Answer 21

Eutrophication
Run off of nutrients means more algae grow in lake
This blocks sunlight for plant species
This means they photosynthesise less so plants die
Saprobiontic bacteria respire aerobically and use O2
Less O2 for fish to respire aerobically

Question 22

The mark-release-recapture method can be used to estimate the size of a
fish population (lines 13–14).
Explain how

Answer 22

Take a sample of fish and add a marker that will not increase risk of predation
Release them and leave them for a while to become fully integrated back into population
Take a second sample and
(Number of fish in 1st sample x number of fish in 2nd sample)/number of marked fish recaptured in second sample

Question 23

Suggest why the mark-release-recapture method can produce unreliable
results in very large lakes (lines 14–15)

Answer 23

Low chance of recapturing fish
Probably not evenly distributed

Question 24

Succession occurs in natural ecosystems. Describe and explain how
succession occurs.

Answer 24

The habitat is initially very inhospitable
Pioneer species that can survive in extreme conditions colonise
Pioneer species cause a change in the environment
This makes it less hostile and more species can now survive there
Causes a change in biodiversity
Until it reaches a climax community

Question 25

Describe how you could estimate the size of a population of sundews in a
small marsh.

Answer 25

Lay down a grid using a measuring tape.
Randomly generate coordinates on the grid
Place a quadrat at the coordinates and count the number of sundews present
Repeat this many times
Calculate an average number of sundews per quadrat
Calculate the area of the marsh and the area of each quadrat
Divide area of marsh by area of quadrat and times the answer by the average number of sundews per quadrat

Question 26

Suggest and explain how digesting insects helps the sundew to grow in soil
with very low concentrations of some nutrients.

Answer 26

Digestion of proteins in insects
Provides amino acids
Digestion of DNA/RNA
Provides nucleotides