UNIT 4 (topic 3) meiosis Flashcards
1
Q
what are the phases of meiosis
A
interphase, prophase I, metaphase I, anaphase I, telophase I/cytokinesis, prophase II, metaphase II, anaphase II, telophase II, after cytokinesis
2
Q
what does meiosis produce
A
4 non-identical daughter cells (gametes)
3
Q
explain interphase
A
- chromosome replicate (DNA synthesis)
- each chromosome has two sister chromatids
4
Q
explain prophase I
A
- chromosomes condense
- nuclear envelope breaks down
- spindle fibres formed
- homologous pairs form bivalents
- chiasma is formed
5
Q
what does bivalent mean
A
homologous pairs slightly overlap
6
Q
what is chiasma
A
two points cross over each other and twist
7
Q
explain metaphase I
A
- spindles attach to centromeres
- bivalents line up on the equator in homologous pairs
- one spindle per homologous pair
8
Q
explain anaphase I
A
- bivalents pulled apart
- maternal and paternal chromosomes separated randomly (independent segregation)
9
Q
explain telophase I/ cytokinesis
A
- chromosomes reach the poles
- often cells go straight to meiosis II but spindles can start to break down (cytokinesis)
10
Q
explain prophase II
A
- spindles form around both sets of chromosomes
- nuclear envelope breaks down if it has reformed
11
Q
explain metaphase II
A
- spindle fibres line chromosomes up along the equator
12
Q
explain anaphase II
A
- spindle fibres contract
- centromeres divide and chromatids divide and chromatids separate
- pulled to the poles
13
Q
explain telophase II
A
- chromosomes reach poles and disperse
- spindles break down
- nuclear envelope reforms
14
Q
explain after cytokinesis
A
- cytoplasm divides
- membranes form
- 4 haploid cells produced (all genetically different)
15
Q
define the term non-disfunction
A
occurs when chromosomes fail to separate in meiosis, leading to offspring having 3 copies or 1 copy of that chromosome
e.g. down syndrome
