Cytogenetics And Molecular Genetics

Question 1

Explain G banding of chromosomes

Answer 1

Dark G bands show heterochromatin- condensed chromatin gene poor

Trypsin can’t degrade chromatin = dark band

Light G bands- euchromatin is uncondensed = trypsin acceded chromatin degrading it = g band light

Question 2

What 2 types of satellite / repeat dna are there

Answer 2

Alpha satellite - centromere repeat

Beta satellite - VNTRs , micro satellites, minisatellites

Question 3

Explain the difference between cytogenetics and molecular genetics

Answer 3

Cytogenetic is whole genome analysis (shows all chromosomes)

Lower base pair resolution

Looks for issues like trisomy in the karyotype

Molecules genetics-

Specific chromosome analysis

Higher 1 Base pair resolution

Uses PCR to amplify small dna parts to analyse base pairs for genetic diseases eg snp analysis

Question 4

When do we analyse chromosomes

Answer 4

During cell division when they uncondense

Question 5

What are the cytogenetic steps of preparing cell culture

Answer 5

They stimulate cell division in the culture

Freeze it in metaphase stage (harvesting)

Banding stain is added

Analysis begins

Question 6

What does constitutional cytogenetics mean

Answer 6

Diseases analysed other than cancers

Question 7

What 3 analyses use cytogenetics

Answer 7

Prenatal cytogenetic analysis

Postnatal cytogenetic analysis

SNP array- taken for better resolution

Question 8

Which 3 techniques are used to study small deletions or abnormalities (molecular)

Answer 8

Fish , QF PCR , snp arrays

Question 9

How are cells taken for analysis in prenatal cytogenetics

Answer 9

Via amniotic fluid or placental tissue

Question 10

Which chromosomes are seen using molecular genetics

Answer 10

Chromosome 13,18 and 21

Question 11

Why are chromosomes 13,18 and 21 analysed

Answer 11

Detect Patau trisomy 13

Edward 18 trisomy

Down 21 trisomy

Question 12

How does QF PCR work to detect abnormalities

Answer 12

Amplification of chromosomes 13,18 and 21 taken

Using primers which flank repeat positions

Quantifies how much dna there is present

If abnormal eg deletions or insertions more testing done

Question 13

What happens if QF PCR is found to be abnormal amounts of dna

Answer 13

Whole genome analysis is done looking at karyotype and this shows things like trisomy etc

Question 14

What kind of chromosome rearrangements can cause trisomy

Answer 14

Robertsonian translocation (fusion of chromosomes)

Question 15

How is postnatal analysis done

Answer 15

QF PCR is done and if abnormal the genome analysis is done

If normal however snp array is done for better resolution incase

Question 16

How do SNPs arrays work

Answer 16

Analyse SNPs of whole genome on wells

Question 17

How are SNPs analysed in the wells of the snp array

Answer 17

Using bead chip techniques

Dna is hybridised with primers with beads attached which stop 1 nucleotide before snp

This then is extending by a labelled nucleotide and this identified the snp base added

Question 18

How can snp arrays show deletions or duplications (inherited due to unequal sister chromatid exchange)

Answer 18

If more or less SNPs are seen through labelled bases

Question 19

Why are deletions picked up better than duplications/trisomy

Answer 19

People are likely fine if they have duplications but can die if they have deletions

Question 20

What happens due to unequal crossing over

Answer 20

Disorders

More or less SNPs on the dna

Question 21

How does fish analysis work

Answer 21

A single DNA sequence called a probe is labelled and annealed with complementary target dna via base pairs

This can detect abnormalities due to deletions or duplications due to the fluorescent probs

Question 22

What is next gen sequencing

Answer 22

Where dna is broken down and has adaptors on the ends

It’s amplified using PCR

The dna library is attached to a flow cells which has oligonucleotides on it

Dna fragments attach to complementary nucleotides on flow cell

The sticky ends of dna fragments then attach to fluorescent nucleotides added

Can compare the sequence to a reference to detect abnormalities

Question 23

What does cancer cytogenetics aim to do

Answer 23

Diagnose, show prognosis and treatment available for the patient

Question 24

What kind of sample is taken for cancer cytogenetics

Answer 24

Sample from skin or bone marrow or blood

Question 25

Give an example of where dna analysis of someone with lymphoblastic leukaemia helped prognosis and treatment

Answer 25

Because if they find hyper diploidy

They have good prognosis and therefore done need treatment unlike people without hyper diploidy

Question 26

Which drug was discovered due to the clear analysis of chronic myeloid leukaemia inversions showing bad prognosis

Answer 26

Imatinib