1.6 cell division Flashcards
what does diploid mean
2 sets of chromosomes
haploid
1 set of chromosones
gametes
sex cells
what are chromosomes
long sections of DNA
what are chromosomes made up of
2 parts that are called chromatids
what are chromatids joined by
centromere
at what point do chromosomes become visible
at the onset of cell division
how many chromosomes do humans have
46
23 pairs of homologous chromosomes
what does mitosis produce
two daughter cells that are genetically identical to the parent cell
what is in the life cycle of somatic cells
-interphase
-mitosis
- cytokinesis
describe interphase
DNA of each chromosome is replicated (copies are called sister chromatids held together at the centromere)
organelles and centrioles replicated
proteins made and the cell carries out its function
4 phases of mitosis
prophase
metaphase
anaphase
telophase
explain prophase
-replicated chromosomes supercoil/ condense (get shorter/ thicker)
-they are then visible under the microscope
-the nuclear envelope breaks down and disappears
- centrioles divide and move to opposite poles
explain metaphase
chromosomes move to the middle of the cell and attaches to the spindle thread (made by the centrioles) by it’s centromere
explain anaphase
the spindle fibres shorten/contract pulling the sister chromatids towards the poles (by their centromeres)
-replicated sister chromatids are separated when the centromere holding them together split
explain telophase
- a new nuclear envelope forms around each set
- spindle fibres break down and disappear
- chromosomes uncoil (no longer visible)
- in this phase the cell has 2 nuclei
where does cytokinesis happen in yeast
called budding
what is interphase split into
Growth phase 1
Growth phase 2
synthesis
where does cytokinesis happen in animals
the centre of the cell, the cytoplasm splits to form a cleavage furrow
what happens during cytokinesis
cell splits to form 2 new cells
each cell has a full set of chromosomes identical to parent cell
spliting is called cytokinesis
where does cytokinesis happen in plant cells
a cell plate made of cellulose is formed at the centre of the cell
what happens during growth phase 1
cytokinesis and organelle replication
growth phase 2?
DNA replication
synthesis
where organelles are made and cells carries out their functiosn
where does mitosis happen
in animal cells it happens in all body cells
in plant cells mitosis only happens in the tips of the roots and the shoots, these are called meristem cells
what can unrestricted cell division lead to
lead to a cancerous growth
what is the length of a cell cycle controlled by
enzymes
what is the enzyme production controlled by
genes, so if the genes are damaged, the cells fail to divide, or divide at the wrong time, divide too much
what are tumour supressor genes
they’re genes that make the enzymes to prevent it
how can some genes cause cancer
if they have mutated or if the cell is infected by a virus (HPV) these are called oncongenes
how is the mitotic index calculated
number of actively dividing cells/
total number of cells x100
significance of mitosis
growth of an organism
repair of tissues (produce genetically identical daughter cells)
asexual reproduction ( bacteria, fungi, strawberries)
explain how the amount of DNA varies during the cell cycle
during interphase the amount of DNA is 1x then during DNA replication it doubles to 2x
during PMAT DNA stays at 2x
and then during cytokinesis it goes back to 1x
describe meiosis
2 cell divisions
one diploid parent cells divide to form four haploid daughter cells that are genetically different to the parent cells
what happens in (prophase) meiosis one that’s the same as mitosis
condensed chromosomes
nuclear envelope breaks down centrioles divide and move to opposite poles
what happens in prophase in meiosis 1 that is different to what happens in mitosis
once chromosome from the mum and one from the dad come together in homologous pairs, each are called bivalents
crossing over happens
explain crossing over
chromosomes pair up, shorten and twist around eachother causing tension. sections of a chromatic may break off and exchange with sections of another chromatid
what is the section called where they break off during crossing over
chiasmata
what happens in metaphase in meiosis 1 that is the same as in mitosis
chromosomes move to the middle of the cell (equator) and becomes attached to a spindle thread (made by the centrioles) by its centromere
what is the extra thing that happens in metaphase in meiosis 1
bivalents arrange themselves at the equator. they lie randomly
what is it called when bivalents lie randomly
independent assortment
what happens in anaphase in meiosis 1
the chromosomes of the bivalents separate as the spindle fibres shorten
each like receives a random arrangement of chromosomes
same as mitosis but NO SPLITTING OF CENTROMERE
what happened in telephone 1 in meiosis 1
the nuclear membrane might reform and the chromosomes uncoil (can no longer see them under a microscope)
Cytokinesis happens
what is the purpose of meiosis 1
variation
purpose of meiosis 11
dividing
sources of variation
(4)
-crossing over and recombination
-independent segregation of chromosomes
- random fertilisation of gameted
- random mating between organisms of the species
when does crossing over and recombination happen
meiosis 1
prophase 1
explain crossing over and recombination
- chromosomes pair up, shorten and twist around eachother causing tension
- sections of chromatid may break off and exchange with sections of another chromatid
explain independent segregation of chromosomes and when does it happen
metaphase 1 - pairs of homologous chromosomes at the equator
they arrange themselves in random order
explain random fertilisation of gametes
during fertilisation, any male gamete can join with any female gamete
thousands of new genetic combinations are possible
significance of meiosis
sexual reproduction
genetic variation
difference in mitosis between plant an animal cells
animal- it happens in all body cells
plant- happens only in the tips of the roots and the shoots which are called the meristem cells
difference in meiosis in animal and plant cells
animal- happens in the gametes (sperm and egg)
plant- meiosis happens in pollen and the egg
difference in cytokinesis in plant and animal cells
animal- splitting happens in the centre of the cell to form a cleavage furrow
plant- a cell plate ( of cellulose) is formed at the centre of the cell
another difference in cell division between plant and animal cells
plant cells don’t have centrioles, still make spindle fibres
however animals cells do have them
differences between meiosis and mitosis
mitosis- growth and repai
meiosis- sexual reproduction
mitosis- one cell division
meiosos- 2 cell divisions
mitosis- cell replication
meiosis- genetic variation
mitosis- diploid cells
meiosis- haploid cells
mitosis- produces genetically identical daughter cells
meiosis- produces genetically different daughter cells
mitosis- in body cells to make body cells
meiosis- reproductive organs to make gametes
mitosis - 2 daughter cells
meiosis - 4 daughter cells
