Meiosis

Question 1

Explain the importance of meiosis in the life cycle of a sexually reproducing organism.

Answer 1

Meiosis halves the number of chromosomes (formation of haploid gametes, eggs and sperm)
Restoration of diploid number at fertilisation;
Introduces variation;

Question 2

Describe what happens to chromosomes in meiosis.(6)

Answer 2

1. Chromosomes condense;
2. Chromosomes associate in homologous pairs (bivalents)
3. Crossing-over (chiasma formation)
4. Join to spindle (fibres) / moved by spindle ;(*)
5. (Join via) centromere
6. (At) equator/middle of cell
7. Independent assortment”
8. (Homologous) chromosomes move to opposite poles /
   chromosomes separate/move apart; (ALLOW ‘are pulled apart’)
9. (Pairs of) chromatids separated in 2nd division;

Question 3

Describe how meiosis causes variation and explain the advantage of variation to the species.(5)

Answer 3

1. Crossing-over;
2. Independent/random assortment/orientation/segregation of (homologous) chromosomes in meiosis I;
3. Independent/random assortment/orientation/segregation of chromatids in meiosis II;
   Advantages of variation, any three from:
4. Different adaptations / some better adapted;
5. Some survive / example described;
6. To reproduce;
7. Pass on gene/allele;
8. Allows for changing environment/different environment/example described;

Question 4

Explain how crossing over can contribute to genetic variation.

Answer 4

Sections of chromatids exchanged;
sections have different alleles;
new combinations of (linked) alleles;

Question 5

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

Answer 5

Mutation;
different/new allele formed / genes deleted or duplicated/ sequence of genes
changed (reject genetic information);
random fusion of gametes in fertilisation;
new combination of alleles;
independent assortment (of chromosomes) (accept random);
shuffling of maternal and paternal chromosomes/new combination
of alleles;