mitosis meiosis Flashcards
what happens during interphase
organelle synthesis occurs in g1 and g2 phase; semiconservative DNA replication occurs in S phase
Mitosis pathway GOGOGOGOGOGO
Prophase: chromatin condenses to form chromosomes. each chromosome comprises 2 sister chromatids joined at the centromere; centrioles move to opp poles and start to organise spindle fibres; nucleolus disapppers and nuclear envelope disintegrates into vesicles
metaphase: chromosomes align at the metaphase plate; each chromosome is attached to 2 kinetochore microtubules at the centromere
anaphase: Centromere of each chromosome divides to form daughter chromosomes ; kinetochore microtubules shorten and pull daughter chromosomes centromere first to opp poles ; non-kinetochore microtubules elongate and slide in opposite directions
telophase:
cytokinesis: cell membrane invaginates towards the equator of the cel, forming a cleavage furrow.
in plant cells; fluid-filled vesicles appear in the middle of the cell and coalesce to form a cell plate
whats PMAT
prophase metaphase anaphase telophase
meiosis prophase 1
P1: chromatin condenses to form chromosomes. each chromosome comprises 2 sister chromatids joined at the centromere.
synapsis occurs -> homologous chromosomes pair up to form bivalents
crossing over occurs between non-sister chromatids of homologous chromosomes, forming chiasmata. exchange of corresponding alleles on non-sister chromatids occurs.
centrioles move to opposite poles and spindle fibres start to form
nucleolus disappears and nuclear envelope disintegrates into vesicles
meiosis metaphase 1
M1: homologous chromosomes align in pairs at the metaphase plate; independent assortment occurs
each chromosome is attached to the kinetochore microtubules from the pole it faces
meiosis anaphase 1
A1: homologous chromosomes separate to opposite poles
each homologue is pulled by a shortening kinetochore microtubule
non-kinetochore microtubules elongate and slide in opposite directions, elongating the cell
meiosis telophase 1
T1: each pole now has a haploid set of chromosomes.
chromosomes decondense to form chromatin
spindle fibres disintegrate. nuclear envelope reforms and nucleolus reappears.
meiosis prophase 2 GOOGOGOGOGOGO
chromatin condenses to form chromosomes. each chromosome comprises 2 sister chromatids joined at the centromere.
centrioles duplicate and move to opposite poles
spindle fibres start to form
nucleolus disappears, nuclear envelope disintegrates.
meiosis metaphase 2
chromosomes align at the metaphase plate in 1 row; each chromosome is attached to kinetochore microtubules from both poles.
meiosis anaphase 2
centromere of each chromosome divides -> each sister chromatid now known as daughter chromosome.
kinetochore microtubules shorten -> pulls daughter chromosomes, centromere first, to opposite poles.
non-kinetochore microtubules elongate and slide in opposite directions -> elongating the cell
meiosis telophase 2
chromosomes decondense to form chromatin
spindle fibres disintegrate
nuclear envelope reforms and nucleolus reappears
cytokinesis: in animal and plant cells
in animal cells: cell membrane invaginates towards the equator of the cell, forming a cleavage furrow. the cleavage furrow deepens and is pinched into 2, producing 2 daughter cells
in plant cells: fluid-filled vesicles appear in the middle of the cell and coalesce to form a cell plate, separating the two daughter cells.
significance of mitotic cycle
production of genetically identical daughter nuclei with same number and type of chromosomes and the same alleles so that genetically identical daughter cells can be produced for
1. growth
2. regeneration and cell replacement
3. asexual reproduction
need to regulate the mitotic cycle tightly
cancer occurs when the dysregulation of checkpoints of cell divison occur or cells escape the cell cycle control mechanism leading to uncontrolled cell division.
significance of meiotic cell cycle
for maintenance of chromosome number in every generation
reduction division: production of 4 haploid gametes from 1 diploid parent cell; chromosome number halved so that the chromosome number can be restored upon fertilisation
2. for genetic variation in offspring in every generation: crossing over between non-sister chromatids of homologous chromosomes results in new combinations of alleles on chromatids; independent assortment of homologous chromosomes at the metaphase plate and their subsequent separation during M1 and A1 and random orientation of non-sister identical sister chromatids of each chromosome at the metaphase plate and their subsequent separation during M2 and A2.
random fusion of gamete during sexual reproduction
