[Maximum number: 3]

The courgette plant, Cucurbita pepo, produces edible fruits that vary in colour and shape.
Fruit colour in courgettes is controlled by the gene A / a.
Fruit shape in courgettes is controlled by the gene B/b.
- A yellow fruit is produced when the dominant allele A is present.
- A round fruit is produced when the dominant allele B is present.

Genes A / a and B/b occur on different chromosomes.
Table 1.1 shows the genotypes and phenotypes of four different varieties of courgette with respect to their fruit colour and shape.

Table 1.1

(a)

Watermelons, Citrullus lanatus, are plants in the same family as courgettes. They produce large round edible fruits that usually contain many hard seeds. Seeds are the structures formed when the male and female gametes fuse at fertilisation.

In the 1990s a triploid (3 n) watermelon plant was developed. To produce the triploid watermelon plant, a normal diploid parent plant ( 2 n=22 ) was crossed with an artificially created tetraploid plant (4 n=44).

Triploid watermelon plants develop edible fruits but these are sterile and do not contain seeds, making them more enjoyable to eat.

Explain why the fruits of the triploid plants are sterile and do not contain seeds.

[ 3 ]

(a)

The cells in Fig. 1.1 are from the same organism and look the same. The cells in Fig. 1.1(a) have been produced by mitosis and the cells in Fig. 1.1(b) have been produced by meiosis.

Fig. 1.1(a)

[ 2 ]

(i)

Explain why the organism produces cells by meiosis.

[ 2 ]

[Maximum number: 1]

Fig. 1.1 shows a cell of a female fruit fly, Drosophila melanogaster, during a stage of mitosis.

Fig. 1.1

(a)

(i)

Shade a pair of homologous chromosomes.

[ 1 ]

(a)

(i)

Suggest what information about the relative distance between the linked genes can be gained from crossover values.

[ 1 ]

[Maximum number: 5]

Yeasts are unicellular organisms from the kingdom Fungi. Saccharomyces cerevisiae is one species of yeast that can carry out either asexual reproduction by mitosis or sexual reproduction by meiosis.

Budding in S. cerevisiae is a process where a small daughter cell forms as a bud on the parent cell. The bud contains a copy of the parent cell nucleus and it eventually separates from the parent cell to form a new cell.
S. cerevisiae can exist in two forms: haploid cells or diploid cells.
- Haploid cells can be one of two different mating types: a and $\boldsymbol{\alpha}$ .
- Haploid cells can only mate with other haploid cells of the opposite mating type.

Key: (a) mating type a

\text { @ mating type } \alpha

Fig. 2.1

(a)

With reference to Fig. 2.1, state the numbers of the stages 1-5 that:
involve mitosis
involve meiosis
produces new genetic variation
shows only haploid cells
shows only diploid cells

[ 5 ]

(a)

After treatment with hFSH, oocytes are collected from mature ovarian follicles and examined to check that they have reached metaphase II of meiosis.

Describe how an oocyte in metaphase I of meiosis can be distinguished from one in metaphase II of meiosis. You may use labelled diagrams to illustrate your answer.

[ 3 ]

[Maximum number: 2]

The patty pan squash plant, Cucurbita pepo, produces edible fruits that vary in colour.

(a)

The colour of the fruits is controlled by two genes, A / a and B / b, that occur on different chromosomes.
- Allele A produces a white fruit colour.
- Allele a does not produce a colour by itself but allows the colours coded by gene B/b to show in the phenotype.
- Allele B produces a yellow fruit colour.
- Allele b produces a green fruit colour.

In a dihybrid cross, an AABB plant was crossed with an aabb plant. All the resulting F1 plants produced white fruits.

The F1 plants were then crossed with each other to obtain the F2 generation.

[ 2 ]

(i)

Plants P and Q show genetic variation with respect to fruit colour alleles.

Identify the process that occurred during meiosis in the F1 parents that produced this variation and the stage of meiosis at which it occurred.
process
stage of meiosis

[ 2 ]

[Maximum number: 2]

The summer squash plant, Cucurbita pepo, produces edible fruits that vary in shape. Fig. 2.1 shows the fruits of three different varieties of squash plants.

Fig. 2.1

Fruit shape in squashes is controlled by two genes, A / a and B / b, that are located on different chromosomes.
- A disc-shaped fruit is produced when both dominant alleles, A and B, are present.
- A spherical fruit is produced when either allele A or allele B is present, but not if both A and B are present.
- A long fruit is produced when both allele A and allele B are absent.

(a)

(i)

The offspring show genetic variation with respect to fruit shape alleles.

Name the process that occurred during meiosis in the parents that produced this variation and state the stage of meiosis at which it occurred.
process
stage of meiosis

[ 2 ]

(a)

The results of the test crosses described in (a)(ii) are shown in Table 2.2.

Table 2.2

[ 4 ]

(i)

Flies with red eye, vestigial wing and flies with purple eye, normal wing phenotypes are described as recombinant.

Name the stage of meiosis when these recombinants are produced and state how this occurs.

[ 2 ]

(ii)

Explain why the results in Table 2.2 are different from the expected ratio of 1: 1: 1: 1.

[ 2 ]