Genetics

Question 1

What are coding and non coding portions of genes called

Answer 1

Coding- Exons

Non coding- introns

Question 2

Which base pairs are purines and which are pyramidines

What is different about RNA

Answer 2

Purines- A and G (earlier in alphabet)
Pyrimidines- T and C

u instead of T

Question 3

What are telomeres

Answer 3

Ends of genes- stop codons to prevent genes getting lost in replication

Question 4

What is unique about mitochondrial DNA (2 things)

Answer 4

Circular

Only present in Eggs so only maternally inherited

Question 5

Mitosis
What is it
What are the stages
What is formed at the end

Answer 5

Division of normally growing cells

Interphase- genetic material doubles 
Prophase- chromosomes pair up 
Metaphase- line up and spindles attach
Anaphase- chromatids pulled apart
Telophase- chromosomes line up at each pole. Cell divides into to 

2 identical daughter cells- DIPLOID

Question 6

Meiosis
What is it
What are the stages- what is different to mitosis
What forms at the end

Answer 6

Formation of egg and sperm
Mitosis one and PMAT2. No interphase 2
4 identical daughter cells which are all HAPLOID

Question 7

What three things can go wrong in mitosis

What can go wrong in meiosis

Answer 7

Mitosis- insertions deletions and single nucleotide substitutions
Meiosis- non dysfunction

Question 8

What is the usual gene issue in CF

What happens in a non sense mutation

Answer 8

Mid sense mutation- different amino acid forms- glutamine changes to valine

A non functional protein occurs

Question 9

What is a robertsonian translocation
What types of chromosomes are involved? What are they? Which ones?
Does it affect the offspring and carrier equally
Give an example

Answer 9

Unbalanced translocation- p arm is lost
Acrocentric ch- centromere is near the end- 14,13,15,21&22
Won’t affect the individual, their offspring are likely to have issues
14:21- 1:8 chance of t21

Question 10

What is imprinting
What causes an imprinting disorder

What is the normal and abnormal imprinting in:
Prader willi 
Beckwith widemann 
Russel silver
Angelman 

Which chromosomes do the above involve?

Answer 10

Normal deletion (methylation) of a gene depending on who it’s inherited from 
Disorder= deletion of the active parents gene or UPD of the inactive 

Prader willi- normal- maternal deletion. Defect is paternal deletion or maternal UPD ch15
BW- ‘ ch 11
Russell silver- normal is maternal deletion. Disease usually only maternal UPD. Ch7. Rarely can be paternal deletion ch 11
Angelman- normal- paternal deletion. Defect is maternal deletion- ch15 or paternal UPD- UBE3A

Question 11

What is gene expression

What are the three stages

Answer 11

Turning a gene into a polypeptide (protein or enzyme)
1- transcription- turn DNA to mRNA- RNA polymerase reads from 3-5 and adds matching base pairs (u substitutes for t)
2- processing- non coding regions removed by splicing
3- translation- ribosome moves along mRNA 5-3. T RNA adds base pairs. Stops at stop codon and releases protein

Question 12

How do you calculate incidence from carrier frequency?

Answer 12

(Carrier frequency squared) x 4

Question 13

What does FISH look for

What are the two types of microarray available? Which finds consanguinity?why? Which shows more mosaicism?

Answer 13

Known microduplications or deletions

CGH- finds mosaicism up to 15%.
SNP- finds to 7%. Finds long stretches of homozygosity- consanguinity

Question 14

What tests are used in whole genome sequencing to find:
RNA
DNA
Protein

Answer 14

Northern blot
Southern blot
Proteins

Question 15

When is NIPT done?

What is the most likely cause of a false positive?

Answer 15

First trimester

Confined placental mosaicism

Question 16

What will a microarray not find

Give an example

Answer 16

Balances Karyotypes

Triploidy

Question 17

Autosomal dominant

What are the rules of transmission. If 1 parent has it what is the risk to offspring?

Answer 17

Can have male to male transmission
Equally affects men and women
50% chance of boys or girls having it

Question 18

Autosomal recessive
What are the rules of transmission
If a sibling has it what does this mean
What is the risk to offspring if 1 parent has the disease

Answer 18

Equally male and female
2/3 chance siblings are carriers. Both Parents have to be carriers
All children are carriers

Question 19

X linked recessive
What is the rule
If mum is a carrier what does this mean?
“If dad is affected

Answer 19

No male to male transmission
50% daughters are carriers, 50% sons affected. Rest normal
All daughters are carriers, no sons are affected

Question 20

X linked dominant
Give 2 examples of conditions
What are the rules

Answer 20

Incontenenti pigmenti, Rett syndrome
Lethal in males
Same as XLR

Question 21

Mitochondrial

What are the rules

Answer 21

Only mum can transmit it. All her children will be affected

Question 22

Which triplet repeats are seen in:
Myotonic dystrophy 
Friederichs ataxia
Huntington’s 
Fragile x

What is unique about the anticipation seen in Huntington’s and MD

Answer 22

Md- CTG
FA- GAA
Huntington’s- CAG
Fragile X- CGG

Huntington’s shows anticipation with paternal inheritance, MD with maternal

Question 23

Which locus is associated with low IQ

Answer 23

15q11.2

Question 24

What three things can exon sequencing not pick up

Answer 24

Balanced things! 
Triplet repeats
Mitochondrial 
Imprinting 
Balanced translocations