Meiosis

Question 1

Define meiosis

Answer 1

• results in production of 4 daughter nuclei
• all haploid, half number of chromosomes as parent cells
• e.g. gametes
• undergoes 2 nuclear divisions
• aka reduction division

Question 2

Why are gametes produced?

Answer 2

• nucleus of male gamete and female gamete fuses during fertilisation (each is haploid)
• form diploid number of chromosomes, maintained in zygote

Question 3

Interphase

Answer 3

• chromatin threads replicate to produce 2 identical sis chromatids
• centrioles replicate

Question 4

Prophase I

Answer 4

• chromatin threads condense, coil and shorten into visible chromosomes
• homologous chromosomes pair up (synapsis) , each pair is a bivalent
• crossing over btw sis chromatids of homologous chromosomes may occur (exchange DNA)
• point of cross over = chiasma
• results in new combi of alleles along chromosomes
• centrioles move to opp ends, nuclear envelope disintegrates, spindle fibres form

Question 5

Metaphase I

Answer 5

• homologous chromosomes arrange themselves along equator (orientation can vary)
• one of each pair faces opp poles
• each chromosome attached to spindle fibre

Question 6

Anaphase I

Answer 6

• homologous chromosomes separate

- one of each pair pulled to opp pole of cell

Question 7

Telophase I

Answer 7

• spindle fibres disintegrates
• nuclear envelope reforms in animal cell only
• most plant cells dont undergo telophase I, move straight to metaphase II)

Question 8

Cytokinesis I

Answer 8

• centrioles replicate (4)

- cytoplasm cleaves/splits to form 2 daughter cells (haploid)

Question 9

Prophase II

Answer 9

• centrioles move to opp poles of cell
• nuclear envelope disintegrates
• spindle fibres appear

Question 10

Metaphase II

Answer 10

• chromosomes line singly along equator

- homologous chromosomes lie next to each other (unlike metaphase I)

Question 11

Anaphase II

Answer 11

• centromeres divide, sis chromatids separated to becomes daughter chromosomes
• daughter chromosomes pulled to opp poles of cell

Question 12

Telophase II

Answer 12

-spindle fibres disintegrate and nuclear envelopes form

Question 13

Cytokinesis II

Answer 13

• cells divide, form 4 daughter cells (each haploid)

Question 14

Importance of meiosis in sexual reproduction

Answer 14

• gives genetic variation (crossing over during prophase I, independent assortment at metaphase I, random seperation of homologous chromosomes at anaphase I)
• fertilisation is random, result in variation
• variation increases chances of survival of species when there are environmental changes

Question 15

Differences between mitosis and meiosis (MITOSIS)

Answer 15

• occur in all cells
• function: growth, repair
• 1 nuclear division, produce 2 diploid cells, same no. of chromosomes as parent
• daughter cells genetically identical to parent cell
• homologous chromosomes dont pair up at prophase, no crossing over
• line up singly (M)
• sis chromatid separate, centromeres divide (A)

Question 16

Differences between mitosis and meiosis (MEIOSIS)

Answer 16

• occur only in reproductive organs
• function: produce gametes
• 2 nuclear divisions, 4 haploid daughter cells (half no. of chromosomes)
• daughter cells are genetically diff (genetic variation)
• homologous chromosomes pair up, crossing over may occur at prophase I
• bivalent line up (M I)
• centromeres don’t divide, homologous chromosomes separated (A I)