Unit 4- Mutations + Meiosis =)

Question 1

Explain how the chromosome number is halved during meiosis. (2)

Answer 1

1. homologous chromosomes
2. each pair moves to each daughter cell

Question 2

Give one reason why trout eggs produced by meiosis are genetically different. (1)

Answer 2

• independent segragation
• /crossing over

Question 3

Farmed female trout are treated so that they produce diploid egg cells.
The offspring produced from farmed trout are sterile. Suggest and explain why. (2)

Answer 3

• extra set (/ 3 copies) of chromosomes
• chromosomes x pair up
• x meiosis

Question 4

Give two differences between mitosis and meiosis. (2)

Answer 4

mitosis vs meiosis:
1. 1 division vs 2
2. 2 daughter cells vs 4
3. genetically identical vs diff.
4. diploid –> diploid vs diploid –> haploid
5. x vs separation of homologous chromosomes
6. x vs independent segragation
7. x vs crossing over

Question 5

On some farms, animals are routinely given antibiotics in their food.
Suggest and explain one reason why bacteria resistant to tetracycline are more common than bacteria resistant to streptomycin in these farm animals. (2)

Answer 5

1. T given ↑ often/ in ↑ doses
2. resistant bacteria ↑ likely to survive –> reproduce ==> pass on allele for resistance
3. gene passed on to ↑ bacteria

//
1. ↑ doses
2. ↑ freq. of mutations for resistance
3. T used over a longer time period
4. ↑ time for mutations to occur

Question 6

In recent years, these farm animals have not been given tetracycline in their food. Despite this, the percentage of bacteria resistant to tetracycline has remained constant.
Suggest one reason why. (1)

Answer 6

• x selection against resistant bacteria
• // r gene passed on when bacteria reproduce
• //environment x changed–> stabilising selection

Question 7

Patau syndrome caused an extra chromosome in one of the chromosomes in a female sufferer. Describe how this change in chromosome number was produced. (2)

Answer 7

• homologous chromosomes x separate
• in meiosis

Non-disjunction can result in the loss of an entire chromosome in one daughter cell, and a gain of a chromosome in another daughter cell.

Question 8

Patau syndrome caused an extra chromosome in one of the chromosomes in a female sufferer.
Explain why all the cells of the body will have this mutation. (2)

Answer 8

• mutation in gamete
• all cells are derived from mitosis
• genetically identical

Question 9

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Define the term mutagenic agent. (1)

Answer 9

a factor that incrases the rate of mutations

Question 10

spore = ball supported by hypha = stick/ stem

The hypha supporting the spore-carrying sporangium is vertical.
Suggest one advantage of the hypha being vertical. (1)

Answer 10

spores spread further

Question 11

Suggest how a mutation in the LCT gene could result in a baby being unable to digest lactose in breast milk or formula. (2)

Answer 11

• mutation –> Δ order of a.a. –> Δ primary structure
• x complementary to a.s.