(02) Cell Division Flashcards
define somatic cell
body cell
define germ cell
egg in females and sperm in males
involved in reproductive cell division
define diploid / haploid
haploid has 23 chromosomes
diploid has full set of 46 chromosomes
stages of interphase
G1 = growth phase
S = synthesis of DNA
G2 = Growth / gap phase 2
describe G1
general life is happening for the cell… cells grow and get larger, many ORGANELLES duplicate
describe S phase
DNA replication
ends up with two copies of all DNA in the cell - NOTE THIS IS DIFFERENT FROM RNA TRANSCRIPTION - we do not cover DNA replication process
describe G2
doing a number of checks in preparation for Mitotic phase
replication of centrosomes completed
name the four stages of the mitotic phase
Prophase
Metaphase
Anaphase
Telophase + cytokinesis
Describe prophase for mitosis
Forming mitotic spindle (made of microtubules (tubulin))
Nucleus condenses into chromosomes
Nuclear envelope disappears so chromosomes are more free
describe metaphase
condensed chromosomes align in the middle
spindles pull it
describe anaphase
spindle fibres contract, separating chromosomes to opposite poles of the cell
describe telophase
nuclear envelope reforms
cleavage
in what forms does DNA exist in each stage of cell division?
usually exists as chromatin (soup)
prophase - condenses into 2 identical sister chromatids per chromosome (attached at centromere)
anaphase - sister chromatids separate
the result of cell division
two daughter cells that are genetically identical to the parent cell
where are mitotic cell checkpoints located
three key checkpoints: G1, end of G2, M
what is checked during the M phase checkpoint?
that all chromosomes are attached to spindles (in the pro-meta phase)
where does meiosis occur?
occurs in the gonads (ovaries and testes)
what does meiosis produce
gametes = haploid cells
they are GENETICALLY DIFFERENT from the parent cell
from diploid to haploid cells - daughter cells have exactly half the number of chromosomes
what are homologous pairs
one maternal and one paternal chromosome that pair up during fertilisation
carry the same genes but not necessarily the same alleles of those genes
name the two stages of meiosis and the main functions
Meiosis I = separates homologous chromosomes
Meiosis II = separates sister chromatids
because both the homologous pairs AND sister chromatids must be separated
so one starting cell can produce four gametes
describe prophase I in Meiosis
synapsis - two sister chromatids of each pair of homologous chromosomes pair up, forming a TETRAD
recombination - non-sister chromatids within these tetrads then cross over
describe metaphase I in Meiosis
homologous PAIRS line up at the metaphase plate
(at random! = random assortment, so gametes with different sets of homologues are formed)
describe anaphase I and telophase I in Meiosis
homologues separate to opposite sides of cells (sister chromatids remain attached)
cleavage, newly formed cells are haploid (2n???)
describe Meiosis II
very similar to mitosis
sister chromatids line up at the middle of the cell
sister chromatids separate in anaphase II
haploid (1n) daughter cells form (4 gametes total per parent) \
differences in DNA replication for mitosis and meiosis
DNA replication occurs during interphase before mitosis, and also interphase before Meiosis I but NOT before Meiosis II
what are sources of genetic variation as a result of meiosis?
crossing over at prophase = recombination
independent assortment at metaphase
fusion between two gametes
