Mitosis / Meiosis

Question 1

define mutagenic agent : (1)

Answer 1

(A factor that) increases (the rate of) mutations;

Question 2

Name the type of mutation that changed the number of chromosomes to produce a species with double the chromosomes (3)

Answer 2

1. Non-disjunction;
2. (In) meiosis;
3. Chromosomes not separated

Question 3

Explain the process of crossing over in meiosis I

Answer 3

• During meiosis I, homologous pairs of chromosomes pair up.
• The chromatids twist around eachother and bits swap over.
• They still contain the same genes, but different alleles.

Question 4

Explain how independent segregation of chromosomes leads to genetic variation

Answer 4

When the homologous pairs are separated during meiosis I, it is completely random which chromosome ends up with which daughter cell

Question 5

What happens during interphase?

Answer 5

• DNA is decondensed
• DNA replication
• replication of organelles
• protein synthesis.

Question 6

What happens during prophase?

Answer 6

• DNA coils and becomes more condensed
• nuclear envelope breaks down
• centrioles produce spindle fibres which attach to the centriomere of the chromosomes

Question 7

Let’s happen during anaphase.

Answer 7

• Spindle fibres shorten and contract.
• This separates the sister chromatids
• so that they are pulled to opposite poles of the cell.

Question 8

Apart from mutation, explain one other way genetic variation within a species is increased: (2)

Answer 8

1. Random fusion of gametes;
2. (Produces) new allele combinations;

Question 9

Female trouts are treated to produce diploid egg cells. Explain why offspring produced from farmed trout or sterile. (3)

Answer 9

1. Too many/extra set/three copies of chromosomes;
2. (Homologous) chromosomes do not pair
   OR
   (Homologous) chromosomes do not separate (evenly);
3. (So) no meiosis;

Question 10

Define ‘gene mutation’ and explain how a gene mutation can have:
* no effect on an individual
* a positive effect on an individual

Answer 10

1. Change in the base/nucleotide (sequence of chromosomes/DNA);
2. Results in the formation of new allele;
   (Has no effect because)
3. Genetic code is degenerate (so amino acid sequence may not change);
4. May result in increased reproductive success