L13- Meiosis Flashcards
meiosis is
division for germ line cells
production of sperm
spermatogenesis
production of eggs
oogenesis
meiosis creates
haploid cells- sperm and eggs
2n–> n
sperm and eggs will
two haploid cells will join at fertilisation and form a couple diploid set- new genome
meiosis produces ……. cells
non-identical
meiosis is one round of replication followed by
two rounds of division to separate sister chromatids
- meiosis 1
- meiosis 2
order of meiosis 1
prophase 1
metaphase 1
anaphase 1
telophase 1
prophase 1
somes begins to condense and pair up(homologous chromosomes (from mums and dad) will look for each other)
- Each chromosome carefully aligns with homologues partner so that two match up at corresponding positions along their full length
- Homologues recombination occurs via crossing over.
homologous recombination occurs via crossing over
o DNA is broken at the same spot on each homologue and exchange part of their DNA
o Crossing over occurs as chiasmata- cross shaped structures where homologues are linked together
o Chiasmata keep homologues connected
o Can have multiple cross overs
metaphase 1
spindle begins to capture chromosomes and move them towards the centre of the cell- metaphase plate
- Each chromosome attaches to microtubule from just one pole of the spindle
- Homologous pairs not individual chromosomes line up for separation.
when homologous pairs line up at the metaphase plate
the orientation of each pair is random
- gametes will have diff set of homologues
anaphase 1
homologues are pulled apart and move apart to opposite ends of the cell
- Sister chromatids of each chromosome remain attached to one another and
don’t come apart
telophase 1
chromosomes arrive at opposite poles of the cell
- Cytokinesis occurs at the same time as telophase I
- Cleavage- formation of two haploid non-identical daughter cells
cells move from meiosis II to II without
copying their DNA
how is meiosis II diff to meiosis I
shorter and simpler
- basically mitosis for haploid cells
cells that enter meiosis II
are haploid and have one chromosome from each homologues pair
but chromosomes still consist of two sister chromatids
prophase II
Chromosome condense and nuclear envelop breaks down- if needed
- Centrosomes move apart
- Spindle forms between them
- Two sister chromatids are captures by microtubules from opposite spindle poles
metaphase II
the chromosomes line up individually along the metaphase plate.
anaphase II
sister chromatids separates and are pulled towards opposite poles of the cell
telophase II
nuclear envelopes form around each set of chromosomes and the chromosomes decondense.
- Cytokinesis splits the chromosome set into new cells
at the end of telophase II you have
4 haploid cells in which each chromosomes has just one chromatid
consequence of meiosis
- Maintaining constant chromosomes number from generation to generation
- Generation of genetic diversity
how does meiosis produce genetic diversity
o Random assortment of chromosomes on the metaplate
o Crossing over of genetic material
spermatogenesis
cell vision to produce male gametes (sperm)
outline spermatogenesis
1) spermtogonium (2n) becomes a primary spermatocyte (2n)
2) spermatocyte undergoes meiosis –> 4 spermatids (n)
3) spermatids mature to sperm
1 spermacyte (2n) –> 4 sperm (n)
how long does spermatogenesis take
60 days
outline oogenesis
1) oogonium (2n) mature to become a primary oocyte (2n)
2) meiosis of primary oocyte (2n) forms 4 haploid cells
describe the 4 haploid cells produced in oogenesis
1 mature ovum
3 polar bodies
length of oogenesis
12-50 years
