2.6 cell division, diversity and cellular organisation Flashcards
the stages of the cell cycle are
mitosis, cytokinesis, interphase
many cells in multicellular tissues don’t have the ability to
divide
during interphase, cells are
between dividing
during mitosis, cells are
dividing and moving to opposite poles of the cell
during cytokinesis, cells are
splitting in two
the stages of interphase are
G1, S, G2
G1 is known as the
growth phase
the purpose of G1 is to
prepare the cell for mitosis
3 things that happen during G1 are…
- organelles duplicate
- cell grows in size
- proteins needed for mitosis are made
S phase is also known as the
synthesis phase
the purpose of S phase is to
replicate DNA so that there are 2 sets for the new cells
by the end of S phase, all chromosomes
have been replicated
during S phase, all - are replicated
DNA strands
the purpose of G2 phase is to
check that the cell is ready for mitosis
what happens in G2 phase
organelles such as mitochondria and lysosomes divide
meiosis is used to create
haploid cells
meiosis occurs in
two divisions
diploid cells have - pairs of chromosomes
23
haploid cells can be called
gametes
why do gametes have to be haploid?
so that they have the right number of chromosomes when they grow alongside another gamete in sexual reproduction
meiosis occurs
after interphase
what happens in meiosis 1?
homologous pairs of chromosomes are separated
what happens in meiosis 2?
sister chromatids from each chromosome are separated
meiosis creates - - gametes which are - -
4 haploid, genetically different
what are the stages in meiosis 1
prophase 1, metaphase 1, anaphase 1, telophase 1
prophase 1 is the first…
stage in meiosis overall
during prophase 1, chromosomes
supercoil to condense, making them visible
during prophase 1, the nuclear envelope
breaks down
during prophase 1, spindle fibres
form from centrioles
4 things that happen during prophase 1
- chromosomes supercoil
- nuclear envelope breaks down
- spindle fires form from centrioles
- chromosomes undergo crossing over
when does crossing over occur?
during prophase 1
crossing over is the…
exchange of DNA between chromatids on homologous chromosomes
the stages of crossing over are
- twisting
- breaking off
- swapping
crossing over allows
variation in alleles
the key purpose of metaphase 1 is to
line up chromosomes at the equator of the cell
independent assortment occurs during
metaphase
independent assortment is how
homologous chromosomes are arranged
independent assortment creates
more genetic variation
3 things that happen in metaphase 1 are
- attachment of chromosomes to spindle fibres at the centromere
- chromosomes lie with their homologous pair at the equator
- independent assortment
how do chromosomes attach to spindle fibres
at the centromeres
spindle fibres are constructed from
centrioles in animals, cytoplasm in plants
the purpose of anaphase 1 is
to separate homologous chromosomes to opposite poles of the cell
in anaphase 1, chromosomes are pulled to opposite poles by
spindle fibres and motor proteins
the purpose of telophase 1 is to
reform two new nuclear envelopes
which type of cell undergoes cytokinesis after telophase 1
animal cells
do plant cells undergo cytokinesis after telophase 1
no
