Meiosis Flashcards
1
Q
Define meiosis
A
- 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
2
Q
Why are gametes produced?
A
- nucleus of male gamete and female gamete fuses during fertilisation (each is haploid)
- form diploid number of chromosomes, maintained in zygote
3
Q
Interphase
A
- chromatin threads replicate to produce 2 identical sis chromatids
- centrioles replicate
4
Q
Prophase I
A
- 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
5
Q
Metaphase I
A
- homologous chromosomes arrange themselves along equator (orientation can vary)
- one of each pair faces opp poles
- each chromosome attached to spindle fibre
6
Q
Anaphase I
A
- homologous chromosomes separate
- one of each pair pulled to opp pole of cell
7
Q
Telophase I
A
- spindle fibres disintegrates
- nuclear envelope reforms in animal cell only
- most plant cells dont undergo telophase I, move straight to metaphase II)
8
Q
Cytokinesis I
A
- centrioles replicate (4)
- cytoplasm cleaves/splits to form 2 daughter cells (haploid)
9
Q
Prophase II
A
- centrioles move to opp poles of cell
- nuclear envelope disintegrates
- spindle fibres appear
10
Q
Metaphase II
A
- chromosomes line singly along equator
- homologous chromosomes lie next to each other (unlike metaphase I)
11
Q
Anaphase II
A
- centromeres divide, sis chromatids separated to becomes daughter chromosomes
- daughter chromosomes pulled to opp poles of cell
12
Q
Telophase II
A
-spindle fibres disintegrate and nuclear envelopes form
13
Q
Cytokinesis II
A
- cells divide, form 4 daughter cells (each haploid)
14
Q
Importance of meiosis in sexual reproduction
A
- 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
15
Q
Differences between mitosis and meiosis (MITOSIS)
A
- 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)