3.4.3 Meiosis & Mutations Flashcards
what is a mutation that occurs in meiosis
nondisjunction - chromosomes do not separate during anaphase in meiosis - causes down syndrome
characteristics of meiosis
- produces daughter cells that are genetically different
- 2 nuclear divisions
- 4 haploid daughter cells
- preceded by DNA replication
process of meiosis
- prophase l
- metaphase l
- anaphase l
- telophase l
- cytokinesis
- prophase ll
- metaphase ll
- anaphase ll
- telophase ll
- cytokinesis
what happens in prophase l
- chromosomes condense and become visible
- homologous chromosomes attach to each other at chiasmata forming bivalent
- spindle fibres form
what happens in metaphase l
- homologous pairs of chromosomes attach to spindle fibres at the equator of the cell
- independent segregation occurs
- crossing over occurs
what happens during anaphase l
- 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
what happens telophase l
- chromosomes uncoil
- spindle fibres break down
- haploid nuclei have formed
what happens in prophase ll
- chromosome condense and become visible
- spindle fibres form
what happens in metaphase ll
- chromosomes line up at the equator of cell and attach to spindle fibres by the centromere
what happens in anaphase ll
- chromosomes separate and chromatids are pulled to the poles of the cell
- spindle fibres contract, pulling the chromatids by the centromeres
what happens in telophase ll
- chromosomes uncoil
- spindle fibres break down
how does genetic variation occur during meiosis
- independent segregation (random lining up)
- crossing over
- random fertilisation
what is independent fertilsation
- 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
how does crossing over result in genetic variation
- sections of non-sister chromatids can be exchanged when the chiasmata breaks
- results in new combinations of alleles on the chromatids
how does random fertilisation cause
- 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
differences between meiosis and mitosis
mitosis: all other body cells, 1 parent cell, produces 2 diploid daughter cells, 1 division, no genetic variation
meiosis: gametes 2 parents cells, produces 4 haploid daughter cells, 2 divisions, genetic variation
what is the probability that independent segregation creates an identical arrangement
1/16
