10.1 Meiosis

The image below shows a pair of chromosomes during meiosis, taking place in a testis of Drosophila melanogaster (a fruit fly). The position of the alleles of some genes is indicated.

State the name of the arrangement of chromosomes shown in the image above.

The diagram below shows two of the gamete nuclei that formed at the end of the meiosis process shown in part a). Assume that the parent cell only contains 2 chromosomes.

Draw the chromosomes in each of the nuclei shown in the diagram to give their appearance at the end of meiosis.

Outline the events that occur during anaphase I of meiosis.

Explain how independent assortment contributes to genetic variation in gametes.

European rabbits (Oryctolagus cuniculus) have a diploid (2n) chromosome number of 44.

The number of possible chromosome combinations that are possible as the result of independent assortment can be calculated using the formula 2ⁿ, where n is the haploid chromosome number.

Calculate the number of different possible chromosome combinations in the gametes of rabbits.

The graph below shows how the mass of DNA changes over time during two different types of cell division of a diploid organism.

Identify, with a reason, which of the division types represents meiosis.

Describe the two processes represented by the letters X and Y in the graph in part b).

The fruit fly (Drosophila melanogaster) has a diploid number (2n) of 8.

The image below shows some cells from different organisms undergoing cell division.

Identify, with a reason, the cell which would represent a fruit fly cell that has just completed meiosis I.

Explain what is meant by the phrase ‘non-Mendelian ratio’.

Explain how the work of Thomas Hunt Morgan provided a possible explanation for non-Mendelian ratios.

Hydra are small, freshwater invertebrates that can reproduce by forming buds on their cylinder-shaped bodies. These buds grow over time, developing tentacles like the adult hydra, and eventually detaching from the parent hydra’s body.

Suggest why meiosis would not occur in Hydra during the process described above.

Describe the process of crossing over in prophase I.

Compare and contrast meiosis II and mitosis.

Draw a diagram to show how chiasmata are formed.