3.4.3 Meiosis & Mutations Flashcards
1
Q
what is a mutation that occurs in meiosis
A
nondisjunction - chromosomes do not separate during anaphase in meiosis - causes down syndrome
2
Q
characteristics of meiosis
A
- produces daughter cells that are genetically different
- 2 nuclear divisions
- 4 haploid daughter cells
- preceded by DNA replication
3
Q
process of meiosis
A
- prophase l
- metaphase l
- anaphase l
- telophase l
- cytokinesis
- prophase ll
- metaphase ll
- anaphase ll
- telophase ll
- cytokinesis
4
Q
what happens in prophase l
A
- chromosomes condense and become visible
- homologous chromosomes attach to each other at chiasmata forming bivalent
- spindle fibres form
5
Q
what happens in metaphase l
A
- homologous pairs of chromosomes attach to spindle fibres at the equator of the cell
- independent segregation occurs
- crossing over occurs
6
Q
what happens during anaphase l
A
- homologous pairs of chromosomes separate and individual chromosomes are pulled to the poles of the cell
- spindle fibres contract, pulling the chromatids by the centromeres
7
Q
what happens telophase l
A
- chromosomes uncoil
- spindle fibres break down
- haploid nuclei have formed
8
Q
what happens in prophase ll
A
- chromosome condense and become visible
- spindle fibres form
9
Q
what happens in metaphase ll
A
- chromosomes line up at the equator of cell and attach to spindle fibres by the centromere
10
Q
what happens in anaphase ll
A
- chromosomes separate and chromatids are pulled to the poles of the cell
- spindle fibres contract, pulling the chromatids by the centromeres
11
Q
what happens in telophase ll
A
- chromosomes uncoil
- spindle fibres break down
12
Q
how does genetic variation occur during meiosis
A
- independent segregation (random lining up)
- crossing over
- random fertilisation
13
Q
what is independent fertilsation
A
- maternal and paternal chromosomes can be positioned either side of the equator of the cell
- which is random for each homologous pair
- results in cells with different combinations of maternal and paternal chromosomes
14
Q
how does crossing over result in genetic variation
A
- sections of non-sister chromatids can be exchanged when the chiasmata breaks
- results in new combinations of alleles on the chromatids
15
Q
how does random fertilisation cause
A
- each individual organism produces genetically varied gametes
- in each fertilisation event there is an equal probability of any female gamete fusing with any male gamete
- increases genetic variation within a species
