Topic 1: Cell Division Flashcards
when did the early study of genetics start?
1865
genes control gene ____ of DNA to RNA, and therefore ______ to proteins
- transcription
- translation
genes are contained in _____
chromosomes
genetic information can also be contained within ______ (plants) and _____ (plants&animals)
- chloroplasts
- mitochondria
what are the three main subdisciplines of genetics?
transmission genetics
evolutionary genetics
molecular genetics
mitosis creates ______
two identical daughter cells
in what kind of cells does mitosis occur?
somatic cells
each somatic cell is ____N (______)
- 2N
- diploid
if human cells are diploid, how many chromosomes do humans have if their diploid state is 2N=46?
23 chromosomes
meiosis creates _____
four unique haploid cells
in what kind of cells does meiosis occur?
germ-line cells, to produce gametes!
what are the six stages of mitosis?
interphase
prophase
prometaphase
metaphase
anaphase
telophase/cytokinesis
in _____,
1. chromosomes are diffuse and not visible
2. chromosomes are duplicated
3. nuclear envelope still encloses the nucleus
4. two centrosomes are in the cytoplasm
5. microtubules begin to extend
interphase
in ______,
1. chromosomes begin to condense and become visible
2. sister chromatids attached via centromeres visible
3. pair centrosomes move to the poles
4. microtubules extend from centrosomes to form the mitotic spindle
5. nucleolus disappears
prophase
in ______,
1. nuclear envelope begins to breakdown
2. mitotic spindle attaches to kinetochores of the sister chromatids
3. microtubules begin exerting pulling forces in both directions
4. chromosomes begin to move to center of the cell
5. cohesion proteins bind sister chromatids together
6. nonkinetochore and astral microtubules stabilise the cell
prometaphase
why do cohesion proteins bind sister chromatids together in prometaphase?
to prevent them from separating early!
in ______,
1. chromosomes are fully condensed
2. chromosomes align to metaphase plate
3. sister chromatids are still attached to kinetochore microtubules extended from centrosomes
4. mitotic spindle fully developed
metaphase
in ______,
1. sister chromatids separate
2. daughter chromosomes move towards opposite poles and congregate at centrosomes
3. non-kinetochore and astral microtubules polymerise, elongating the cell
anaphase
“_______”: sister chromatids separate
disjunction
in _____, cohesion proteins break down and kinetochore microtubules depolymerise
disjunction (when sister chromatids separate in anaphase)
in ______ & ______,
1. non-kinetochore microtubules continue polymerising (elongating the cell)
2. nuclear envelope redevelops
3. chromosomes decondense
4. cytokinesis divides the cytoplasmic contents equally between daughter cells
5. nucleolus reforms to continue creating proteins/ribosomes again
telophase/cytokinesis
what does cytokinesis form in plants to divide the two daughter cells? in animals?
- cell plate
- contractile ring and cleavage furrow
during mitosis the number of chromosomes _____
doesn’t change
during mitosis, the number of chromatids _____
doubles in S phase, goes back to normal after anaphase
if we have 2ng of DNA in G1, we have ____ after S phase and ____ after anaphase (M phase)
- 4ng
- 2ng
_________, pass if cell size is adequate, nutrients are available, presence of growth factors
G1 checkpoint
what do growth factors do?
regulate cyclin kinases
______, pass if DNA replication is complete and base-pair mismatches/errors are removed
S-phase checkpoint
_____, pass if cell size is adequate, chromosome replication is complete
G2 checkpoint
_______, pass if all chromosomes are attached to the mitotic spindle
metaphase checkpoint
which 3 of the 4 main checkpoints does a cell HAVE to pass to continue on in the cell cycle?
G1, S-phase, G2
the cell can still function if it doesn’t pass the metaphase checkpoint
meiosis has ___ rounds of cell division
2
is there DNA replication between meiosis I and II?
no!
_____ -homologous chromosomes separate, ploidy level is halved
meiosis I
____- sister chromatids separate
meiosis II
which phase of meiosis is most similar to mitosis?
meiosis II
what are the three main hallmark events of meiosis I?
- homologous chromosome pairing
- crossing over between homologous chromosomes
- segregation of homologous chromosomes
what does chromosome synapsis mean?
crossing over!
crossing over between homologous chromosomes results in ____
recombination
where does recombination occur?
at chiasmata (crossing-over sites)
what are the five sub-stages of prophase I?
leptotene and zygotene, pachytene and diplotene, diakinesis
______: chromosomes are duplicated, chromosomes condense but not visible, centrosomes migrate to poles, spindle fibers produced
leptotene
_____: chromosomes continue condensing, homologous pairs enter synapsis (forming the synaptonemal complex), meiotic spindle forms, and the nuclear envelope begins to break down
zygotene
what is the synaptonemal complex?
3-layer structure that forms during prophase I, tightly binds non-sister chromatids of homologous chromosomes
______: chromosome condensation is partially complete, synapsed homologs are seen as bivalents (tetrads), crossing over occurs between non-sister chromatids (formation of chiasmata), kinetochore microtubules attach to the kinetochores, nuclear envelope breakdown continues
pachytene
_____: crossing over is complete, synaptonemal complex dissolves but chiasmata remain, tetrads are completely visible, the nuclear envelope is fully dissolved
diplotene
_____: meiotic spindle established, homologous chromosomes tethered to poles via spindle fibers, nuclear envelope fully degraded, tetrads move to cell middle
diakinesis
______: tetrads align at to the metaphase plate, homologous pairs are tethered to opposite poles, kinetochores of sister chromatids are attached to the same centromere and joined by cohesion proteins, chiasmata linking non-sister chromatids are broken
metaphase I
metaphase I allows recombination via ______
independent assortment
independent assortment allows for ____ different combinations (where n= number of homologous pairs)
2^(n-1)
anaphase I (_____ of alleles)
segregation
______: kinetochore microtubules depolymerise, disjunction occurs (pulling homologies to opposite poles), sister chromatids remain attached by cohesion, ploidy level has now been reduced by half
anaphase I
_____ & ________: nuclear membrane re-form around chromosomes, chromosomes partially decondense, cytokinesis divided the cytoplasmic contents (which may now be uneven), progeny cells are now haploid
telophase I and cytokinesis
___:
1. nuclear envelope breaks down
2. centrosomes duplicate and migrate to poles
3. microtubules form
4. chromosomes recondense
prophase II
_____:
1. sister chromatids attached to kinetochore
2. align at metaphase plate
metaphase II
_____:
1. sister chromatids separate, breakdown of cohesion proteins
2. kinetochore microtubules deploymerise (shorten)
3. sister chromatids move to opposite poles
anaphase II
_____ & _____:
1. chromosome migration complete
2. chromosomes decondense
3. nuclear envelope reforms
4. cytokinesis divided the cytoplasm
telophase II and cytokinesis
chromatids are _____ in S-phase, then ____ in meiosis I and then _____ again in meiosis II
- doubled
- halved
- halved
number of chromosomes stay _____ in S-phase, then are _____ in meiosis I and remain ____ in meiosis II
- the same
- halved
- halved
how many chromosomes and chromatids does a gamete have?
23 chromosomes, 23 chromatids
_______= failed chromosomal separation
nondisjunction
where does nondisjunction occur?
meiosis I or II
what does nondisjunction cause?
aneuploidy, missing or extra chromosomes
