Topic 7 Exam Questions: Genetics, Populations, Evolution & Ecosystems

Question 1

7.1 - Inheritance and the Hardy-Weinberg Principle

In fruit flies, males have XY chromosomes and females have XX. A gene for eye colour is carried on the X chromosome. Allele for red eyes = R (dom), allele for white eyes = r (recessive).
Male fruit flies are more likely than female fruit flies to ha and white eyes. Explain why. (2)

Answer 1

1. Males have one allele
2. Females need two recessive alleles or need to be homozygous recessive

Question 2

7.1 - Inheritance and the Hardy-Weinberg Principle

Mutation is one cause of genetic variation in organisms. Give two other causes of genetic variation. (2)

Answer 2

1. Crossing over
2. Independent segregation/ assortment (of homologous chromosomes)
3. Random fusion of gametes OR random fertilisation

Question 3

7.1 - Inheritance and Hardy-Weinberg Principle

In genetic crosses, the observed phenotypic radius obtained in the offspring are often not the same as the expected ratios. Suggest two reasons why. (2)

Answer 3

1. Small sample size
2. Linked genes
3. Fusion/fertilisation if gametes is random
4. Epistasis
5. Lethal genotypes

Question 4

7.1 - Inheritance and Hardy-Weinberg Principle

What is meant by the term phenotype? (2)

Answer 4

1. (Expression/appearance/characteristic due to) genetic constitution/genotype/allele(s)
2. (Expression/appearance/characteristic due to) environment

Question 5

7.1 - Inheritance and Hardy-Weinberg Principle

Suggest two reasons why observed ratios are often not the same as expected ratios. (2)

Answer 5

1. Fertilisation is random OR random fusion of gametes
2. Small/not large population/sample
3. Selection advantage/disadvantage/lethal alleles

Question 6

7.1 - Inheritance and Hardy-Weinberg Principle

The student wished to test her results with the ones she expected. Which statistical test should she use? (1)

Answer 6

Chi squared OR x2

Question 7

7.1 - Inheritance and Hardy-Weinberg Principle

In fruit flies, the genes for body colour and wing length are linked. Explain what this means. (1)

Answer 7

(Genes/loci) on same chromosome

Question 8

7.1 - Inheritance and Hardy-Weinberg Principle

Which statistical test could the scientist use to determine whether his observed were significantly different from the expected results? Give a reason. (2)

Answer 8

1. chi squared test
2. categorical data

Question 9

7.1 - Inheritance and Hardy-Weinberg Principle

Mitochondrial disease (MD) often causes muscle weakness. Use your knowledge of respiration and muscle contraction to suggest explanations for this effect of MD. (3)

Answer 9

1. Reduction in ATP production by aerobic respiration
2. Less force generated because fewer actin and myosin interactions in muscle
3. fatigue caused by lactate from anaerobic respiration

Question 10

7.1 - Inheritance and Hardy-Weinberg Principle

Suggest how the change in the Nicholson of tRNA leads to MD (3)

Answer 10

1. change to tRNA leads to wrong amino acid being incorporated into protein
2. tertiary structure (of protein) changed
3. protein required for oxidative phosphorylation/the Krebs cycle, so less / no ATP made

Question 11

7.2 - Populations

What is a gene pool? (1)

Answer 11

All the ALLELES in a population

Question 12

7.2 - Populations

Scientists investigated the frequency of KDR minus allele in a population of mosquitoes over 10 years and is resistant to the pesticide DDT. Suggest an explanation for why the allele of KDR increased substantially over the period (4)

Answer 12

1. Mutation produced KDR minus/resistance allele
2. DDT User provides selection pressure
3. mosquitoes with KDR minus allele more likely (to survive) to reproduce
4. leading to increase in KDR minus allele in population

Question 13

7.3 - Evolution

They observed each female guppy for 10 mins and recorded which makes they were attracted to, they were separated by a transparent barrier. Repeated this with 45 small brained females and 45 large brained females. Suggest three possible limitations of this investigation (3)

Answer 13

1. laboratory raised female guppies might not react/behave/choose the same way as wild guppies
2. (transparent) barrier might not show for normal (courtship) behaviour/interaction
3. don’t know if guppies have been used in previous experiments
4. 10 mins might not be long enough for females to make a final choice OR not enough time for females to make a final choice

Question 14

7.3 - Evolution

The scientists found that only female guppies with large brains were attracted to male guppies brought in colour. Suggest and explain the advantage of this behaviour to the propulsion of guppies. (3)

Answer 14

1. (females with large brains) will mate with males bright in colour
2. their (male) offspring would be (more likely) brought in colour
3. (bright in colour make) offspring could attract larger brained females
4. the population/offspring could (evolve to) have large brains
5. the population/offspring are better at identifying avoiding predators

Question 15

7.3 - Evolution

Describe how sympatric speciation could occur. (3)

Answer 15

1. not geographically isolated
2. (leading to) reproductive isolation OR gene pool kept separate
3. changes in allele frequencies
4. cannot breed/mate to produce fertile offspring

Question 16

7.3 - Evolution

One hypothesis for LP (lactase persistence) in humans suggests that the selective pressure was related to some human populations farming cattle as a source of milk. Describe how farming cattle add a source of milk could have led to an increase in LP. (4)

Answer 16

1. LP due to mutation OR allele due to mutation
2. Milk provides named nutrient
3. Individuals with LP more likely to survive and reproduce OR individuals with advantageous ALLELE more likely to survive and reproduce
4. directional selection
5. frequency of ALLELE increases (in offspring/next generation)

Question 17

7.3 - Evolution

Explain why the number of people with LP allele would rapidly increase one selection for this condition has been established. (2)

Answer 17

1. dominant allele
2. (always) expressed/show (when present in phenotype/offspring) OR expressed when only one (dominant allele) present

Question 18

7.3 - Evolution

Suggest how two species of palm tree arose by sympatric speciation. (5)

Answer 18

1. Occurs in same habitat/environment/population
2. Mutation/s caused different flowing times
3. Reproductive separation/isolation
   OR no gene flow OR gene pools remain separate
4. Different allele/s passed on/ selected
5. DISRUPTIVE (natural) selection
6. Eventually different species cannot (inter) breed to produce fertile offspring

Question 19

7.3 - Evolution

Suggest and explain two reasons why there’s a high frequency of the E280A mutation in Yaramul (2)

Answer 19

1. Isolated so inbreeding/low genetic diversity/small gene pool
2. ALLELE inherited (through generations) from (common) ancestor

Question 20

7.3 - Evolution

Explain why natural selection has not reduced the frequency of the E280A mutation in the population (2)

Answer 20

1. AD/symptoms develops late
2. Have already reproduced

Question 21

7.3 - Evolution

One farmer stated that the increase in the use of Bt crop plants has caused a mutation in one of the insect species that this Munson has spread to other species of insect. Was he correct? Explain. (4)

Answer 21

No
1. Mutations are spontaneous/random
2. Only the rate of mutations is affected by environment
3. Different species do not interbreed/do not produce fertile offspring
4. Soo mutation/gene/allele cannot be passed from one species to another

Question 22

7.3 - Evolution

There was a time lag between the introduction of Bt crops and the appearance of the first insect species that was resistant to the Bt toxin. Explain why there was a time lag. (3)

Answer 22

1. Initially one/few insects with favourable mutation/allele
2. Individuals with (favourable) mutation/allele will have more offspring
3. Takes many generations for (favourable) mutation/allele to become the most common allele (of this gene)

Question 23

7.3 - Evolution

Explain how different subspecies of giraffe may have evolved from a common ancestor. (5)

Answer 23

1. No interbreeding/gene pools are separate/geographical isolation
2. Mutation linked to different marking/colours
3. Surgeon/survival linked to (different) markings/colours
4. Adapted organisms breed /differential reproductive success
5. Change/increase in allele frequency/frequencies

Question 24

7.3 - Evolution

Biologists compared the mitochondrial DNA of 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 (2)

Answer 24

1. (Compare DNA) base sequence /base pairing/ (DNA)
2. Different in six (species)/different in different species/similar in three (subspecies)/similar in same species/subspecies