Unit 7 - Inheritance

Question 1

Define phenotype (2)

Answer 1

1. Expression of genetic constitution of a genotype
2. And its interaction with the environment

Question 2

Define genotype (1)

Answer 2

1. The genetic constitution of an organism

Question 3

If a gene is sex-linked on the X chromosome, why is the phenotype more common in XY organisms? (2)

Answer 3

1. Males have one allele
2. Females need 2 recessive alleles

Question 4

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

Answer 4

1. Crossing over
2. Independent segregation
3. Random fertilisation

Question 5

In genetic crosses, the observed phenotypic ratio obtained in the offspring are often NOT the same as the expected ratios. Suggest TWO reasons why. (2)

Answer 5

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

Question 6

Name the relationship between 2 alleles when both alleles appear in the phenotype. (1)

Answer 6

1. Co-dominance

Question 7

Name the type of gene interaction when one gene affects the expression of another. (1)

Answer 7

1. Epistasis

Question 8

Explain what it means when two genes are linked. (1)

Answer 8

1. On the same chromosome

Question 9

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

Answer 9

1. Chi-squared test
2. The data is categoric

Question 10

Define gene pool (1)

Answer 10

1. All the alleles of each gene in a population at a given time.

Question 11

Define species (1)

Answer 11

1. Organisms that can interbreed to produce fertile offspring

Question 12

The conditions under which the Hardy-Weinberg principle applies (5)

Answer 12

1. No mutations occur
2. Random mating
3. Large population
4. Population is isolated (so no migration)
5. No selection

Question 13

What are the two equations used in the Hardy-Weinberg equation (2)

Answer 13

1. p + q = 1
2. p² + q² + 2pq = 1

Question 14

Describe allopatric speciation (5)

Answer 14

1. Geographical isolation
2. Reproductive isolation/Gene pools remain separate
3. Different selection pressures
4. Variations due to mutations
5. Different ALLELES passed on/Change in frequency of ALLELES
6. Eventually different species cannot interbreed to produce fertile offspring

Question 15

Why does speciation take a long time? (3)

Answer 15

1. Initially few organisms will have the favourable allele/mutation
2. Individuals with the favourable allele will reproduce more and have more offspring.
3. Takes many generations for the allele to become the most common allele

Question 16

Natural selection in resistant strains (5)

Answer 16

1. Some organisms naturally resistant
2. Due to mutations
3. These survive when non-resistant ones are killed (due to pesticide/antibiotic)
4. And they reproduce and pass on the favoured allele
5. Increase in frequency of allele for resistance

Question 17

Describe sympatric speciation (5)

Answer 17

1. NOT geographically isolated
2. Mutation causes reproductive isolation
3. Gene pools kept separate/no gene flow
4. Different alleles passed on
5. Cannot breed to produce fertile offspring

Question 18

Define community (1)

Answer 18

1. All organisms of every species in the same area at a given time

Question 19

Mark, Release, Recapture - Assumptions (4)

Answer 19

1. No migration
2. No losses due to predation
3. Marking does not affect survival
4. Birth rate and death rate are equal

Question 20

Describe how you could estimate the size of a population using random sampling (4)

Answer 20

1. Use a grid
2. Method of obtaining random coordinates (RNG)
3. Count number/frequency in a quadrat
4. Large sample AND calculate mean
5. Valid method of calculating total number of plant (e.g mean number of plants per quadrat multiplied by number of quadrats)

Question 21

Why do you need a large sample size? (1)

Answer 21

1. So more representative

Question 22

Why random sampling? (1)

Answer 22

1. To avoid bias

Question 23

The scientist used % cover rather than frequency to record the abundance of algae present. Suggest why (1)

Answer 23

1.Too many to accurately count / too small / overlap

Question 24

Describe use of systematic sample to count plants (4)

Answer 24

1. Systematic sampling, place quadrats at regular intervals
2. Transect line from/to….
3. Count number/frequency in a quadrat
4. Large sample AND calculate mean number per quadrat

Question 25

Effect of increased plant/animal diversity on ecosystem (3)

Answer 25

1. Increase in diversity of plants leads to more variety of food for animals 2. Increase in diversity of animals leads to an increase in predator species 3. Increase in more different niche/habitat

Question 26

Define niche (3)

Answer 26

1. Role a species plays in a community 2. Includes food resources 3. No two species can occupy identical niche

Question 27

Succession (5)

Answer 27

1. Colonisation by pioneer species 2. Pioneer species change the abiotic conditions (GIVE EXAMPLE HOW) 3. Environment becomes less hostile for new species (Accept older species being outcompeted) 4. Increase in biodiversity 5. To climax community

Question 28

Predator-prey relationship (4)

Answer 28

1. As pest numbers increase, there's also more food for predators so they increase too. 2. Increased predation of pests/prey reduces numbers of prey 3. Low number of pests result in less food for predators so their numbers decrease 4. Low predator numbers allow prey population to increase as less eaten.

Question 29

Succession - competition (3)

Answer 29

1. Pioneer species increase and then decreases 2. Principle of a species changing the conditions / a species makes the conditions 3. New / named species better competitor / pioneer species outcompeted

Question 30

Give TWO features of a climax community (2)

Answer 30

1. Same species present over a long time / stable community 2. Abiotic factors constant 3. Stable populations

Question 31

Suggest ONE reason for conserving woodlands. (1)

Answer 31

1. Conserving habitats 2. Conserving endangered species 3. Reduces global warming (as CO2 is taken up) 4. Source of medicines, etc