MCBHD

Question 1

what kind of polymorphism leads to Huntington’s disease

Answer 1

microsatellites
tandem repeat = CAG coding for glutamine
>36

Question 2

what unit used to measure distance between 2 loci

Answer 2

centimorgans

1cM=1 million base pairs

Question 3

define genotype and haplotype

Answer 3

genotype = 2 alleles in 1 locus

haplotype = combination of alleles on 1 homologue (chromosome)

Question 4

type of common variations

Answer 4

common = SNPs from failure of polymerase proof reading + mismatch repair system
- biallelic

micro satellites = repeats of tandems/loss of tandems from DNA polymerase stuttering
-multiallelic

mini satellites (larger than micro)

copy number variants from non-allelic homologue recombination in meiosis
= missing/extra gene on chromosome

Question 5

how to detect microsatellites

Answer 5

micro satellites have a unique flanking sequence (specific to each micro satellite but the same in all individuals)

• PCR
• GEL ELECTROPHORESIS

we can work out if they have it + if they are heterozygous or homozygous for that micro satellite

Question 6

definition of learning disability

Answer 6

reduced ability to learn/understand new/complex information

and manage independently

Question 7

difference between thalassemia and sickle cell

Answer 7

thalassemia = low NUMBER of haemoglobin

sick cell = bad FUNCTION of haemoglobin

Question 8

what does combined risk score include

Answer 8

maternal age
nuchal translucency (if >3.5mm cause of concern)
beta HCG
PAPP-A levels

Question 9

single gene triplet repeat expansion disorders

Answer 9

eg. huntingtons (CAG >36)
myotonic dystrophy (CTG IN DMPK gene, 4-37 is normal)

Fragile X syndrome
X-linked so usually seen in men (women carriers)

• repeats may expands on transmission
• who it is transmitted from can effect likelihood/expansion
• genetic anticipation ( earlier onset in next generation)

Question 10

autism characteristics

Answer 10

can be independent to LD

but if LD is associated –> likely to be genetic

• impaired imagination
• impaired social interaction
• impaired (social) communication

Question 11

ideal genetic marker properties and therefore what do we use

Answer 11

• polymorphic
• random
• frequent in genome
• known location in genome
• easy to assay

SNPs and MICROsatellites (mini satellites are not random)

Question 12

recombination fraction

Answer 12

number of recombinant / total outcome

Question 13

Are genetic markers variable within an individual

Are genetic markers variable between individuals

Answer 13

NO

YES