Module 4 - Genetic diversity can arise as a result of mutation or during meiosis

Question 1

6 marks

Describe what happens to chromsomes in meoisis

Answer 1

1. Chromosomes condense
2. Chromosomes associate in homologous pairs
3. Crossing over
4. Join to spindle fibres
5. at equator of cell via centromere
6. Homologous pairs move to opposite poles
7. Pairs of chromatids seperated in 2nd division

Question 2

4 marks

Explain crossing over

Answer 2

1. Chromatids can become twisted around each other
2. This puts tension on chromatids
3. Causing pairs of the chromatid to break
4. Broken parts of chromatid recombine with another chromatid
5. =New combination of alleles

Question 3

4 marks

Describe and explain meoisis that result in genetic variation within a species

Answer 3

• In metaphase I of meoisis crossing over between homologous pairs= variation in gametes
• Also in metaphase I independent segration of the homologous pairs leads to variation of different alleles in the gametes
• Random fertlisation of gametes
• New combination of alleles in gametes

Question 4

Explain how chromosome number is halved

Answer 4

1. Homologous chromosomes (pair);
2. One of each (pair) goes to each (daughter) cell / to opposite poles;

Question 5

2 marks

Explain why meosis is important in sexual reproduction, apart from producing gametes that are genetically different

Answer 5

1. Produces haploid cells
2. Restoring diploid number
3. Introduces genetic variation

Question 6

3 marks

Explain how crossing over can contribute to genetic variation

Answer 6

1. Sections of chromatids exchanged
2. Sections have different alleles
3. New combination of alleles

Question 7

5 marks

Meiosis results in genetic variation in the gametes which leads to variation in the offspring formed by sexual reproduction.
Describe how meiosis causes this variation and explain the advantage of variation to the species.

Answer 7

1. Crossing over
2. Independent segregation
3. Random fertilisation
4. Different adaptations
5. Some survive
6. To reproduce
7. Pass on allele

Question 8

The offspring produced from farmed trout are sterile. Suggest and explain why.

Answer 8

1. Too many copies of chromosomes
2. Homologous chromosomes do not pair
   OR
   Homologous chromosomes do not separate
   evenly
3. So no meiosis

Question 9

4 marks

Describe how the process of meiosis results in haploid cells.
Do not include descriptions of how genetic variation is produced in meiosis.

Answer 9

1. DNA replication
2. Two divisions
3. Separation of homologous chromosomes in first division
4. Separation of sister chromatids in second division
5. Produces 4 haploid cells

Question 10

Define homologous pair of chromosomes

Answer 10

2 chromosomes that carry the same genes