Methods of chromosomal analysis Flashcards
centromeres hold together sister chromatids and attach to spindle fibers
what are the different types of chromosomes
Telocentric- centromere towards the end , they are not present in humans
Acrocentric- centromere near one of the ends
Metacentric- centromere in the middle, p arm and q arm about equal length
Submetacentric- centromere slightly away from centre
What are the 7 groups of autosomes
Group A (1-3): metacentric and submetacentric 2
Group B (4-5): large submetacentric
Group C (6-12): medium submetacentric
Group D ( 13-15): medium acrocentric
Group E ( 16-18): short submetacentric
Group F (19-20) : smallest metacentrics
Group G ( 21-22) : small acrocentric (y chromosome)
what do the acrocentric groups carry
Nuclear organizers- these make nucleolus as they carry rRNA genes
What is a karyotype
What is cytogenetics
A species specific characteristic of chromosomes
the study of the structure and function of chromosomes: uses FISH,CGH and chromosome banding
What is chromosome banding
why is metaphase chromosomes specifically used
produces a series of bands along the metaphase chromosomes allowing to see the individual chromosomes and also specific segments
Metaphase used as chromosomes are already condensed
What is a idiogram
graphical representation of chromosome banding- depends on the banding technique
Can detect aneuploidy, chromosomal rearrangements like translocation ( exchange a whole segment to a non homologous chromosome)
What are some chromosomal abnormalities that can be detected using cytogenetics
Robertsonian translocation: fusion of 2 acrocentric chromosomes therefore chromosome number reduced
Turner syndrome: only 1 X chromosome (only affcet female)
Klinefelters: XXY
Down syndrome: trisomy 21
Patau syndrome: trisomy 13
How is the female normal and functioning with turner syndrome
only 1 X chromosome
Bc normal people with 2, have Barr body anyway which is inactive
So Females with turner only need that 1 X that works- dosage compensation
HOWEVER, no fertility
Can down syndrome be inherited
Down syndrome is due to extra copy of chromosome 21
However in some cases, it can be heritable from mother and father
Due to Robersonionian translocation in previous generation where chromosome 21 attaches to another chromosome= this is how its related to human evolution
What is the main cause of chromosomal abnormalities
Problems in oogenesis
- When trying to have baby older, you may have premature destruction of chiasmata bc of long period of arrest ( holds together maternal and paternal homologous pairs)
results in aneuploidy
Eg smaller chromosome (telomeres shorten) means less chiasmata so more likely for aneuploidy
How to obtain dividing cells for karyotype
Embryo- amniotic fluid
Adult- Direct: bone marrow punction (invasive)
Indirect: peripheral blood (wbcs), then incubate in
growth factors. Easier and less invasive.
Why cant you obtain dividing cells from the mouth
bc most cells are apoptotic
Process of karyotyping:
- Arrest chromosomes from tisue/blood sample in metaphase using drug colchicine that affects spindle
- Incubate in HYPOTIONIC solution so cells swell and membrane unstable
- To put chromosomes on slide surface, drop them from a height which ensure the chromosomes spread on the slide
- Fixation to the slide by methanol and acetic acid (destroys proteins except DNA and alc removes water)
- Then, choose a banding method and follow the steps for that
what banding technique is the basic technique for chromosomal analyses
G banding
What is involved in G banding
- Slide incubated with trypsin- digests euchromatin and heterochromatin in different amounts
- Giemsa stain applied- dark region hetero and light region euchromo as trypsin digested it more
- slow process to produce human karyotype from this (1 week)
