Cell Division and Genetics Flashcards
What happens in prophase I of meiosis?
Synapsis - exchange of chromosomal segments
Homologous chromosomes allign together forming a synapse, bound tightly by cohesin at the centromere and a protein lattice, the “synaptonemal complex” then non homologous sister chromatids exchange genetic material.
In metaphase I of meiosis, how is genetic variation introduced?
Random/independent assortment of homologous tetrads
Compare anaphase I and anaphase II of meiosis
I-HOMOLOGOUS PAIRS are pulled apart by microtubules attached to the kinetochore
-so sister chromatids remain attached at the centromere
vs
II-SISTER CHROMATIDS are pullled apart by microtubules attached to the kinetochore
meosis I vs meiosis II
Meiosis I
- allignment of 23 bivalents/tetrads
- pulls apart homologues from eachother
- daughter cells have 23 chomosomes (each with 2 chromatids)
vs
Meiosis II
- allign as independent chromosomes
- sister chromatids pulled apart
- daughter cells have 23 chromosomes ( each with 1, genetically unique chromatid)
What is aneuploidy and how does it most commonly arise?
-odd chromosome number (extra/missing)
arises via NDJ-Non Disjunction either in meiosis I or meiosis II.
What is mosaicism? How can it arise?
Detect via…
The presence of 2 or more genetically different cell lines derived from a single zygote.
Arises via NDJ or anaphase lag
Detect via karyotype
- What is Turners syndrome?
- How does it occur?
- Features
XO - a nullisomic gamete fertilised with an X sperm.
Paternal meiotic errors
Thick skin behind neck, lymphoedema, short stature, infertile, heart defects
- What is Klienefelters Syndrome?
- How does it occur?
- Features
XXY - Disomic XX gamete fertilised with a Y sperm, physically male
Occurs via NDJ of maternal X chromosome
Tall, reduced 2dry sex characteristics, gynaecomastia, infertile
FISH - stages
looks for specific sequence
takes around 1 week
- fluorescent probe
- denature probe and target DNA
- mix probe and target DNA
- Probe binds to target
QF-PCR detects what?
Using what?
takes 48hrs
How many copies of a chromosome the patient has
Microsatellites-short repeated sequences e.g. short tandem repeats, distributed across the whole genome, you use primers (oliognucleotides) for microsatellites known to be on a faulty gene
(After PCR, you measure the fragment length to determine the number of repeats in the microsatellite)
What can FISH detect?
Aneuploidy
Translocations
Large deletions
Reciprocal Translocations are…
and occur by…
exchange of segments between non-homologous chromosomes. They occur spontaneously during meiosis. Seen via karyotype.
via NHEJ-non homologous end joining DNA repair mechanism.
(high recurrence risk)
What are by Robertsonian Translocations?
Which chromosomes can be affected?
2 arms joined with loss of satellites. (cell now has 45 not 46 chromosomes)
Acrocentric (13, 14, 15, 21, 22)
Array CGH-detecting deletions/duplications: 4 steps
no hypothesis needed
- patient and control DNA labelled with fluorescent dyes and applied to the microarray
- patient and control DNA compete to hybridise to the array
- the microarray scanner measures the fluroescent
- computer software analyses the data and generates a plot
What is skewed x inactivation?
in most cells women switch off one of the X chromosomes by random x inactivation but -10% women have uneven, skewed x inactivation.
If this occurs leading to expression of the mutant gene copy, symptoms may occur, these are “manifesting carriers”
