mitosis and meiosis (topic 4) Flashcards
what does mitosis do and what is it used for
cell division in all cells excluding gametes
- 2 daughter cells are genetically identical to parent cells (unless mutation)
important for:
organism growth,
tissue repair/cell replace,
reproduction eg bacteria
what is interphase
the period of time cells are not dividing (90% of the time), you can just see the nucleus and cell membrane in a microscope, chromosomes are not visible
DNA replication occurs => 46 chromosomes become still 46 chromosomes due to centromere (92 chromatids)
/ chromosome (one chromatid)
X also chromosome (sister chromatids)
mitosis - prophase
chromosomes become visible, condense (short+fat)
nuclear membrane disintegrates
spindle fibres start to develop from centrioles at opposite poles
mitosis - metaphase
sister chromatids line up along the equator of the cell because spindle fibres attach to the centromeres and pull them into position
mitosis - anaphase
sister chromatids are pulled apart to opposite poles, spindle fibres contract and pull on the centromeres
mitosis - telophase
nuclear envelopes reform
chromosomes recoil (long+thin) and become invisible
spindle fibres disintegrate
cytokinesis
splitting of cytoplasm => 2 genetically identical daughter cells
mitotic index equation
= (P+M+A+T) / total no of cells x100
prophase, metaphase, anaphase, telophase
what does chemotherapy aim to do
blocks some part of the cell cycle to stop the growth of the cancer
- prevent dna replication, or metaphase by interfering with spindle formation
sex cells chromosomes
have 23 chromosomes each (haploid)
meiosis prophase I
nuclear envelope disintegrates and nucleolus disappears
centrioles move to opposite and spindle fibres start to form
chromosomes condense (short and fat) becoming visible
pair up in homologous chromosomes
meiosis metaphase I
pairs of homologous chromosomes line up along the equator
crossing over can occur between homologous chromosomes (exchange genetic material)
- recombinant chromosomes are formed
meiosis anaphase I
spindle fibres contract, pulling pairs of homologous chromosomes apart to opposite poles
meiosis telophase I
nuclear envelope and nucleolus reform
chromosome recoil (long and thin) become invisible
then cytokinesis
meiosis prophase II
nuclear envelope disintegrates and nucleolus disappears
chromosomes condense (short and fat) and become visible
centrioles move to opposite poles and spindle fibres form
meiosis metaphase II
sister chromatids (chromosomes) line up along the equator (due to spindle fibres attached to centromeres)
meiosis anaphase II
spindle fibres contract pulling sister chromatids apart to opposite poles
meiosis telophase II
nuclear envelope and nucleolus reform
chromosomes recoil (long and thin) becoming invisible
meiosis cytokinesis 2 (product)
4 genetically different daughter cells
each have 23 chromosomes and 23 chromatids (haploid)
meiosis - independent segregation
meiosis is random, 2 chromosomes that pair up will randomly mix when gametes form
(metaphase, they could move around which means they get separated into different daughter cells)
meiosis - genetic recombination
each pair of chromosomes lie side by side, so genes can cross over
calculate possible number of combinations of chromosomes in each daughter cell
(2^n) (n = no of pairs of homologous chromosomes)
eg humans = 2^23 = 8,388,608
after fertilisation: (2^n)^2
homologous chromosomes
copies of the chromosome with same size and gene position
=> eg one from mother one from father
