AQA A level Bio 4.3 Genetic diversity via mutation

Describe what is happening to the chromosomes at the stage shown in Figure 2 (2)

Homologous chromosomes are pulled to opposite poles of the cell by spindle fibres (1)

Describe and explain the appearance of one of the chromosomes in cell X (3)

Chromosomes is formed by two chromatids (1)

which are joined together at the centre by centromere (1)

as DNA replication has occured (1)

Describe what has happened during division 1 in the figure above (2)

Homologous chromosomes are separated are pulled to opposite poles of the cell (1)

One of each into daughter cells (1)

Homologous chromosomes carry the same genes but they are not genetically identical. Explain why (1)

Homologous chromosomes carry different alleles (1)

Figure 2 shows three pairs of homologous chromosomes in a cell at the end of cell division.

The appearance of each chromosome in Figure 2 is different from those shown in Figure 1. Explain why. (1)

Chromatids have not replicated (1)

The diagram shows a cell undergoing cell division.

Identify the type and stage of cell division shown. Give evidence from the diagram to support your answer. (3)

Anaphase I in meiosis (1)

Chromosomes are moving apart (1)

Chromosomes still double structures (1)

Explain one way in which the behaviour of chromosomes during meiosis produces genetic variation in gametes. (1)

Different combinations of maternal and paternal chromosomes (1)

What is the biological importance of reducing the chromosome number when the cell divides by meiosis? (2)

restoring diploid (1)

Later fertilisation (1)

Give two processes, other than crossing over, which result in genetic variation. Explain how each process contributes to genetic variation (4)

Process- Mutation (1)

Explanation - new allele formed (1)

Process - new combination of alleles (1)

Explanation- independent segregation (1)

Describe how crossing over occurs during meiosis I (2)

Chromosomes in each pair twist around each other (1)

Chromatids break and rejoin to chromatid on sister chromosome (1)

Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how (6)

Homologous chromosomes pair up (1)

Crossing over/chiasmata form (1)

Produces new combination of alleles (1)

Chromosomes separate (1)

at random (1)

Product varying combinations of chromosomes (1)

During meiosis, one chromosome from each homologous pair goes to each of the cells produced. Explain why this is important. (2)

To get haploid (1)

so that each cell gets one copy of each chromosome (1)

The diagram shows the life cycle of a fern plant. Drawings of the chromosomes during cell division are shown for the stages that give the spore-producing plant and the gamete-producing plant.

Are the male and female gametes produced by mitosis or meiosis

Explain your answer (2)

(Mitosis because) zygote gets 2 chromosomes from each gamete (1)

Gamete-producing plant has 2 chromosomes so mitosis produce gametes with 2 (1)

Explain how crossing over can contribute to genetic variation. (3)

Sections of chromatids exchanged (1)

Sections have different alleles (1)

New combinations of linked alleles (1)

Crossing over greatly increases genetic diversity in this species of moss.

Describe the process of crossing over and explain how it increases genetic diversity (4)

Homologous pairs of chromosomes associate (1)

Chiasmata form (1)

Alleles are exchanged (1)

Producing new combinations of alleles (1)