mitosis & meiosis Flashcards
where is DNA found in the cell
nucleus and mitochondria
what are the DNA complementary base pairs
A and T
C and G
how many hydrogen bonds are there between A & T
2
how many hydrogen bonds are there between C & G
3
how does DNA coil
it coils around nucleosomes, then again into supercoils and then again into chromosomes
how many chromosomes in human genome
46 (22 pairs + sex chromosomes)
how many genes on each chromosome
several hundred
how long is the continuous DNA duplex on each chromosome
around 10 to power of 7 bp
what do you call the long arm of a chromosome
q
what do you call the short arm of a chromosome
p
what separates the two arms of a chromosome
centromere
what stains can be used to identify chromosomes
giemsa (G banding) & Quinacrine (Q banding)
how many chromosome bands does G banding give
around 400 - 500
what is the telomere
section of DNA at the end of a chromosome
what does the telomere do
stops chromosomes from unravelling
why do we need mitosis (2 reasons)
1) growth
2) to replace dead cells
what are the stages of the cell cycle
G1, S, G2, Mitosis
what is interphase
G1, S, G2
what is the G0 phase
contains cells that are mitotically inactive and not in the cell cycle
what happens in G1
cell grows and replicates content
what happens in S
chromosomes replicate
what happens in G2
cell prepares for mitosis and checks for errors
what are the stages of mitosis
prophase, prometaphase, metaphase, anaphase, telophase
what happens in prophase
chromatin condenses into chromosomes
mitotic spindles begin to form
centrosomes nucleate microtubules and move to opposite poles of nucleus
what happens in prometaphase
nuclear membrane breaks down
microtubules invade nuclear space
chromatids attach to microtubules
spindle fibres attach to chromosomes at the kinetochore
what happens in metaphase
chromosomes line up along the equatorial plane/ metaphase plate(middle of the cell)
helps to ensure sister chromatids are split evenly between the two daughter cells
what happens in anaphase
spindle fibres contract
sister chromatids separate and are pulled to opposite poles of the cell because the centromere is broken
spindle fibres not attached to chromatids will elongate the cell to prepare it for division
what happens in telophase
cell has elongated and is nearly finished dividing
nuclear membranes reform
chromosomes unfold into chromatin
cytokinesis begins
what happens in cytokinesis
cytoplasm divides to form 2 genetically identical daughter cells
how does mitosis affect tumours
helps to categorize them as benign or malignant
lots of mitosis means they are more likely to be malignant
what are the clinical uses of mitosis (3)
detecting chromosome abnormalities
categorising tumours as benign or malignant
can grade malignant tumours - gives an idea about their biological behaviour
which anti cancer drugs attack the mitotic spindle
taxol
vinca alkaloids - vinblastine,vincristine
which anti cancer drugs attack anaphase
colchicine like drugs
which anti cancer drug attacks spindle poles
ispinesib
can mitosis occur in all body cells
yes
can meiosis occur in all body cells
no
in what cells does meiosis occur
gametes only
what occurs in meiosis
the recombination of genetic material to generate diversity
how many cell divisions are there in meiosis
2 - meiosis I and II
what are the products of meiosis
4 haploid daughter cells
what are the stages of meiosis
interphase, prophase I, prometaphase I, metaphase I, anaphase I, telophase I, cytokinesis, interphase II, metaphase II, anaphase II, and telophase II
what happens in meiosis I
homologous chromosomes are separated and reduction from diploid to haploid cells occurs
what happens in prophase I
nuclear membrane breaks down
chromosomes condense
spindle fibres appear
crossing over occurs between non-sister chromatids at chiasmata resulting in genetic diversity
[genes sort independently thus if 1 gene switches over, doesn’t mean another one will],
what happens in metaphase I
maternal and paternal versions of the same chromosome (homologous chromosomes) align along the equator of the cell.
random/independent assortment occurs on the metaphase plate - also resulting in genetic diversity
what happens in meiosis II
sister chromatids seperate
haploid cells produced
define gametogenesis
the process by which gametes, or germ cells, are produced in an organism
what are primordial germ cells
the primary undifferentiated stem cell type that will differentiate towards gametes: spermatozoa or oocytes
what is the first stage of gametogenesis
the proliferation - (rapid increase in the amount of something) of primordial (undifferentiated) germ cells (developing gametes) by mitosis
describe gametogenesis in males
Primordial germ cells > lots of mitoses > spermatogonia (mature sperm)
when does gametogenesis start in males
at puberty
and continues throughout life
but
some mitosis occurs in embryonic stages to produce primary spermatocytes present at birth
how long does sperm production take
60 - 65 days
how many sperm are produced
100 - 200 million
describe gametogenesis in females
Primordial germ cell > 30 mitoses > oogonia
Oogonia enter prophase 1 of meiosis 1 by 8th month of intrauterine life (in-utero)
then the Process is suspended
Cells enter ovulation 10-50 years later
Cytoplasm divides unequally - 1 egg & 3 polar bodies
how does the cytoplasm divide in males during sperm production
evenly
how does the cytoplasm divide in females during egg cell production
unevenly
when is meiosis I completed in egg cell production
at ovulation
when is meiosis II completed in egg cell production
it is only completed if fertilisation occurs
what is non-disjunction
Failure of chromosome pairs to separate in Meiosis 1 or sister chromatids to separate properly in meiosis 2.
can occur in prophase I or II
can result In down syndrome or monosomy (loss of a chromosome)
what causes down sydnrome
non-disjunction at chromosome 21 resulting in trisomy 21
likelihood of this happening increases with the age of both men and females
what is gonadal mosaicism
Occurs when precursor germline cells to ova or spermatozoa are a mixture of two or more genetically different cell lines (due to errors in mitosis)
* One cell line is normal, the other is mutated
* Incidence increases with advancing paternal age
* Parent is healthy ( since genetic change is only in the germline so all the other cells are unaffected - have usual genetic components), but the foetus may have genetic diseases
what inheritance pattern is gonadal mosaicism most common in
autosomal dominant and X linked
even though it can be observed with any
examples of diseases with gonadal mosaicism
oesteogenesis imperfecta
duchenne muscular dystrophy
