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Mutation is one cause of genetic variation in organisms - AQA - A-Level Biology - Question 6 - 2020 - Paper 2

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Mutation is one cause of genetic variation in organisms. Give two other causes of genetic variation. 1 2 In a species of flowering plant, the T allele for tallne... show full transcript

Worked Solution & Example Answer:Mutation is one cause of genetic variation in organisms - AQA - A-Level Biology - Question 6 - 2020 - Paper 2

Step 1

Give two other causes of genetic variation.

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Answer

  1. Crossing over: This process occurs during meiosis where homologous chromosomes exchange genetic material, leading to new combinations of alleles.

  2. Random fertilization: The random fusion of gametes during fertilization contributes to genetic variation as it creates unique genetic combinations.

Step 2

Name the relationship between the two alleles that code for flower colour.

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Answer

The relationship between the two alleles is termed codominance, where both alleles are expressed in the phenotype of the heterozygote.

Step 3

Phenotypes of parents:

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Answer

Dwarf, pink-flowered × Tall, white-flowered

Step 4

Genotypes of parents:

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Answer

Dwarf, pink-flowered: ttC^R C^W (assuming pink is heterozygous for colour) and Tall, white-flowered: TtC^W C^W

Step 5

Genotypes of offspring:

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Answer

Possible genotypes: TtC^R C^W, TtC^W C^W, ttC^R C^W, ttC^W C^W

Step 6

Phenotypes of offspring:

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Answer

Tall pink-flowered, Tall white-flowered, Dwarf pink-flowered, Dwarf white-flowered

Step 7

Ratio of phenotypes:

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Answer

The expected ratio of phenotypes is 1 (tall pink): 1 (tall white): 1 (dwarf pink): 1 (dwarf white), resulting in a ratio of 1:1:1:1.

Step 8

Calculate the percentage of pink-flowered plants.

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Answer

Let p = proportion of red-flowered plants = 0.09. Using Hardy-Weinberg, p^2 + 2pq + q^2 = 1 where q² (percentage of red-flowered plants) = 0.09.

Therefore, q = √0.09 = 0.3, and p + q = 1, thus p = 1 - 0.3 = 0.7 (proportion of pink-flowered plants).

The percentage of pink-flowered plants = 2pq = 2(0.7)(0.3) = 0.42 or 42%.

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