2.6 cell division, diversity, organisation Flashcards
name the phases of the cell cycle
interphase
mitosis
cytokinesis
name the phases and describe what happens in interphase
g0= resting phase, cells may die, differentiate
G1= first growth phase, cell increases in size, organelles duplicate, genes transcript, protein synthesis
S= synthesis, DNA replicates
G2= second growth phase, cell checks for errors
what happens at the checkpoints
cell cycle halted and checked
g1= DNA damage, cell size etc.
g2=prevents cell replicating if DNA error from replicating
why are there checkpoints in the cell cycle
prevent uncontrolled cell division
detect/repair DNA damage
ensure cell cycle cannot be reveresed
DNA is only duplicated once
why do cells undergo mitosis
asexual reproduction
tissue growth and repair
name the stages of mitosis
prophase
metaphase
anaphase
telephase
what happens in prophase
chromosomes condense and become visible
spindle fibres form by centriole splitting and moving to opposite poles
nuclear envelope breaks down
what happens in metaphase
pairs of chromatids line up in the middle
spindle fibres attach to centromeres
what happens in anaphase
centromere of each pair of chromatids split
spindle fibres pull apart (motor proteins)
what happens in telephase
new nuclear membrane forms
cell now contains two nuclei that are genetically identical
what happens in cytokinesis
cell splits in two
plasma membrane and cytoplasm spilt
2 daughter cells formed
what is the significance of meiosis
sexual reproduction
fertilisation
haploid cells/gametes
what are homologous chromosomes
matching chromosome pairs containing the same genes (diff. alleles)
name the stages of meiosis
prophase 1
metaphase 1
anaphase 1
telephase 1
p2
m2
a2
t2
what happens at prophase 1
p1= chromatin condenses, chromosomes supercoil, nuclear envelope break down, spindle fibres form, chromosomes come together in homologous pairs, crossing over occurs
what happens at metaphase 1
bivalents attach along equator, spindle attaches to centromere, independant assortment occurs (random)
what happens at anaphase 1
pairs of h.c are pulled apart
what happens at telephase 1
spindle fibres break down
two new nuclear membranes form around each set of chromosomes
what happens during cytokinesis after stage 1 of meiosis
division of cytoplasm and plasma membrane
produces two haploid cells
what happens at prophase 2
the two new nuclear envelopes break down, chromosomes condense and spindle forms
what happens at metaphase 2
chromosomes line up at equator attached by centromere
what happens at anaphase 2
centromeres divide, chromatids pulled apart and randomly segregated
what happens at telophase 2
nuclear envelope form around each of 4 haploid nuclei
how does meiosis produces genetic variation
crossing over during prophase
independant assortment
what is independant assortment
production of different combinations of alleles in daughter cells due to random allignment of homologous pairs along the equator of the spindle during metaphase 1
what are stem cells
unspecialised cells that are pluripotent