NSC Life Sciences Genetics and Inheritance: 2.1 The leaf colour in a plant i

Question

2.1 The leaf colour in a plant is controlled by two alleles, green (G) and yellow (g). Thorns on plant stems are controlled by two alleles, presence of thorns (T) and no thorns (t).

Two plants with the genotypes GGTT and ggtT were crossed. Their offspring were then left to pollinate each other.

The table below shows the possible genotypes of the offspring of the second generation. Genotypes (i) and (ii) have been left out.

| Gametes  | GT   | Gt   | gT   | gt   |
|----------|------|------|------|------|
| GT       | GGTT | GGtT | GgTT | GgTt |
| Gt       | GGtT | GGtt | GgTt | ggtT |
| gT       | GgTT | GgTt | ggTT | ggTt |
| gt       | GgTt | ggtT | ggTt | ggtT |

2.1.1 Give the:
(a) Genotype of (i)
(b) Phenotype of (ii)

2.1.2 List the FOUR genotypes of the offspring of the second generation that would be phenotypically different from the original pair of parents.

2.2 The diagram below represents a phase in meiosis.

Cell 1 undergoes division to give rise to cells 2 and 3. Some alleles are indicated by letters.

2.2.1 Explain why cell 1 does NOT belong to a human.

2.2.2 How many chromosomes would be present in:
(a) Cell 2 at the end of telophase I
(b) The daughter cells produced by cell 3 after meiosis II

2.2.3 Draw a labelled diagram of a gamete that will result from cell 2.

2.4 Huntington's chorea is a disease caused by a gene mutation that results in the degeneration of brain tissue. It is caused by a dominant allele (H).

The pedigree diagram below shows the inheritance of this disorder in a family.

What is:
(a) Susan's phenotype
(b) Sarah's genotype

Emma plans to have a baby. What must the father's genotype be so that there is a 50% chance that their child will not have Huntington's chorea?

Explain your answer to QUESTION 2.4.2.

2.5 The mutation that causes Huntington's chorea occurs when the CAG base triplet on the DNA molecule is repeated more than 35 times. This mutation results in the formation of a 'Huntington's protein', which causes the degeneration of neurons in the brain.

The diagram below shows the process whereby an mRNA molecule is formed from the DNA molecule.

2.5.1 Name the process represented in the diagram.

2.5.2 Where in the cell does this process occur?

2.5.3 Give the:
(a) Complementary bases on DNA strand 2 for a CAG triplet
(b) Sequence of bases at X

2.5.4 Which amino acid will occur more than 35 times in a 'Huntington's protein'?

2.5.5 Explain how a mutation results in the formation of a different protein.

2.6 You have two rose plants, both with pink flowers. You cross them and find that, while most of the offspring are pink, some are red and some are white.

Use a genetic cross to show how breeding two pink flowering plants can result in pink, red and white offspring. Use the letter R for the red allele and W for the white allele.

2.1 The leaf colour in a plant is controlled by two alleles, green (G) and yellow (g) - NSC Life Sciences - Question 2 - 2016 - Paper 2

Worked Solution & Example Answer:2.1 The leaf colour in a plant is controlled by two alleles, green (G) and yellow (g) - NSC Life Sciences - Question 2 - 2016 - Paper 2

Genotype of (i)

Phenotype of (ii)

List the FOUR genotypes of the offspring of the second generation that would be phenotypically different from the original pair of parents.

Explain why cell 1 does NOT belong to a human.

How many chromosomes would be present in: (a) Cell 2 at the end of telophase I

How many chromosomes would be present in: (b) The daughter cells produced by cell 3 after meiosis II

Draw a labelled diagram of a gamete that will result from cell 2.

Susan's phenotype

Sarah's genotype

What must the father's genotype be so that there is a 50% chance that their child will not have Huntington's chorea?

Explain your answer to QUESTION 2.4.2.

Name the process represented in the diagram.

Where in the cell does this process occur?

Give the: (a) Complementary bases on DNA strand 2 for a CAG triplet

Give the: (b) Sequence of bases at X

Which amino acid will occur more than 35 times in a 'Huntington's protein'?

Explain how a mutation results in the formation of a different protein.

Use a genetic cross to show how breeding two pink flowering plants can result in pink, red and white offspring.

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