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GCSE · Biology

IG.B8 Meiosis and the Causes of Variation

EDEXCEL 4BI1 · Calculator allowed · about 60 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

Define meiosis, as used in the production of gametes in animals and plants, naming the number of cells produced and whether they are genetically identical or different.

(Total for Question 1 is 2 marks)

State the haploid and diploid chromosome numbers relationship that meiosis establishes for sexual reproduction, as required for fertilisation to restore chromosome number.

(Total for Question 2 is 1 mark)

Describe, for the topic of meiosis in 4BI1, how the chromosome number is halved during the division process in a diploid cell.

(Total for Question 3 is 2 marks)

Explain why it is necessary for meiosis to halve the chromosome number before fertilisation in sexual reproduction, referencing zygote chromosome number.

(Total for Question 4 is 2 marks)

Explain two ways in which genetic variation arises between gametes and therefore between offspring of the same species, naming meiosis and another source.

(Total for Question 5 is 2 marks)

Distinguish between continuous and discontinuous variation, giving one clear example of each within the context of organisms of the same species.

(Total for Question 6 is 2 marks)

Interpret the following histogram data for height in a plant population in a school biology class experiment. Heights (cm): 10 plants at 6-8 cm, 20 plants at 8-10 cm, 30 plants at 10-12 cm, 20 plants at 12-14 cm, 10 plants at 14-16 cm. (a) State whether this distribution is continuous or discontinuous. (b) Describe the shape of the histogram and what it suggests about typical plant height.

(Total for Question 7 is 3 marks)

Define mutation, in the context of genetic variation, and state whether mutations are usually harmful, beneficial or neutral.

(Total for Question 8 is 2 marks)

Explain briefly how a mutation can lead to variation within a species, using the effect on a protein or phenotype in your answer.

(Total for Question 9 is 2 marks)

Give one example of a variation caused mainly by genetics and one caused mainly by the environment, naming the organism or human trait in each example.

(Total for Question 10 is 2 marks)

A student wants to investigate whether different amounts of fertiliser affect the height variation of identical fast-growing bean plants. Describe a simple method for this investigation, including the independent variable, dependent variable and two control variables to make the test fair.

(Total for Question 11 is 3 marks)

In a population survey for blood groups, 18 out of 60 people sampled had blood group O. Calculate the percentage of people with blood group O to one decimal place.

(Total for Question 12 is 3 marks)

State briefly why gametes produced by meiosis are genetically different from each other, in the context of producing variation within a species.

(Total for Question 13 is 1 mark)

Explain the causes of variation between organisms of the same species. In your answer include genetic causes and environmental causes, and explain how these together produce the variation seen in a population.

(Total for Question 14 is 6 marks)

Mark scheme · IG.B8 Meiosis and the Causes of Variation

Question 1

B1 a type of cell division that produces gametes
B1 produces four haploid cells that are genetically different from each other and from the parent cell
Answer: Meiosis is a cell division that produces four haploid gametes which are genetically different

Question 2

B1 meiosis halves the diploid number to make haploid gametes so fertilisation restores the diploid number
Answer: Meiosis halves the diploid number to haploid so fertilisation restores the diploid number

Question 3

B1 the cell divides twice (two successive divisions)
B1 sister chromatids or homologous chromosomes are separated so daughter cells have half the chromosomes
Answer: The cell undergoes two divisions so homologous chromosomes/sister chromatids are separated, producing cells with half the chromosome number

Question 4

B1 halving prevents chromosome number doubling every generation
B1 fertilisation restores the diploid number so the zygote has the correct chromosome number
Answer: Halving prevents chromosome number doubling each generation, because two haploid gametes fuse at fertilisation to restore the correct diploid zygote chromosome number

Question 5

B1 variation arises in meiosis because the four gametes are genetically different (award phrasing that meiosis produces different combinations)
B1 variation also arises from random fertilisation or mutation named as a second source
Answer: Meiosis produces genetically different gametes, and additional variation arises from random fertilisation or from mutations in DNA

Question 6

B1 continuous variation: shows a range of values, e.g. height
B1 discontinuous variation: distinct categories, e.g. blood group
Answer: Continuous variation shows a range of values such as height; discontinuous variation falls into distinct categories such as blood group

Question 7

B1 identifies the distribution as continuous
B1 describes the shape as roughly bell-shaped or symmetric with a peak in the 10-12 cm class
B1 states that most plants are around 10-12 cm (the mode), suggesting a typical or average height in that range
Answer: a) Continuous. b) Roughly bell-shaped with a peak at 10-12 cm, so most plants are around 10-12 cm tall

Question 8

B1 a change in the DNA sequence (or gene) of an organism
B1 most mutations are neutral or harmful, with beneficial mutations being rare
Answer: A mutation is a change in an organism's DNA sequence; most mutations are neutral or harmful, beneficial ones are rare

Question 9

B1 mutation can change a gene so it codes for a different protein or a nonfunctional protein
B1 this change can alter the organism's phenotype, producing variation among individuals
Answer: A mutation can alter a gene so a different or nonfunctional protein is made, changing the phenotype and so producing variation among individuals

Question 10

B1 one genetic example, e.g. blood group in humans or flower colour determined by genes
B1 one environmental example, e.g. plant height affected by nutrient availability or tan in humans caused by sun exposure
Answer: Genetic example: human blood group. Environmental example: plant height affected by nutrient availability

Question 11

B1 identifies independent variable: amount or concentration of fertiliser and how to vary it (e.g. none, low, medium, high)
B1 identifies dependent variable: plant height measured after a fixed time
B1 states two control variables, e.g. same light, same soil type and volume, same watering schedule, same number and age of seeds
Answer: Vary fertiliser amount (e.g. none, low, medium, high) as independent variable; measure plant height after a set time as dependent; keep seed type, soil, light and water the same as control variables

Question 12

M1 forms the fraction 18/60 and multiplies by 100
A1 percentage = 30.0% cao
B1 gives answer to one decimal place as 30.0% or equivalent
Answer: 30.0%

Question 13

B1 because meiosis produces different combinations of genes in each gamete (leading to genetic differences)
Answer: Because meiosis produces gametes with different combinations of genes so each gamete is genetically different

Question 14

Level 1 (1-2): Simple statements about one or two causes of variation, with limited development. May list examples without clear explanation.
Level 2 (3-4): Clear explanation of genetic and environmental causes with some linking showing how they produce differences in traits. Some correct use of terminology.
Level 3 (5-6): Detailed explanation covering genetic causes, mutation and random fertilisation, plus environmental influences, and a coherent synthesis of how these factors interact to produce the range of variation in a population
Indicative content:
- Genetic causes: different alleles inherited from parents determine traits
- Meiosis produces different combinations of alleles and gametes are genetically different
- Random fertilisation of gametes mixes alleles from two parents producing new combinations
- Mutation introduces new alleles or changes to genes that can alter traits
- Environmental causes: factors such as nutrition, light, temperature, disease, and exercise can change phenotype without changing the genotype
- Interaction: the same genotype can give different phenotypes in different environments, and genetic variation provides the raw material on which environmental selection acts, producing the observed range of traits in a population

Meiosis and the Causes of Variation - Worksheets, Questions and Revision