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Flashcards in Genetic risk calculations Deck (22)
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1
Q

Cystic fibrosis

A

commonest autosomal recessive disease affecting caucasians
incidence 1/2500
250 babies/ year
carrier frequency is 1/25
mutation of the CFTR
main defects in the lungs and pancreas caused by thickened mucus

2
Q

sickle cell disease

A

incidence 1/1900
abnormal haemoglobin causing sickling of RBCs
haemolytic anemia, abnormal cells block small vessels, shortened life span

3
Q

pedigree symbol for deceased

A

diagonal line through shape

4
Q

pedigree symbol for divorced/ separated

A

double small lines across marriage line

5
Q

pedigree symbol for when partners are blood relatives

A

double line between 2 people

6
Q

what is it called when partners are blood relatives

A

consanguineous

7
Q

pedigree symbol for twins

A

2 diagonal lines

8
Q

pedigree symbol for unknown sex children

A

diamond with number inside

9
Q

pedigree symbol for miscarriage

A

triangle/ small square or circle

10
Q

how to calculate risk to unborn child of autosomal recessive disease ?

A

mother carrier risk x father carrier risk x 1/4

11
Q

working out carrier risk

A

probability of being a carrier halves for each degree of relationship away from the known carrier in a family

12
Q

what is a first degree relative?

A

a parent, sibling or child

13
Q

what is a second degree relative ?

A

uncle, aunt, nephew, niece, grandparent, grandchild or half-sibling

14
Q

carrier risk of an autosomal condition if there is no family history

A

population risk of being a carrier
different populations = different risk
Difficult to count carriers in a population as they are unaffected.
Can be calculated using hardy weinberg equation of the incidence is known

15
Q

what are the hardy weinberg equations?

A

p+q = 1

p2 + 2pq + q2 = 1

16
Q

what does p and p2 represent in hardy weinberg equations?

A

normal allele

p2 = homozygous normal frequency, unaffected, not a carrier

17
Q

what does q and q2 represent in hardy weinberg equations?

A

mutant allele

homozygous mutant frequency - affected

18
Q

what does 2pq represent in hardy weinberg equations?

A

heterozygous frequency - carriers

19
Q

using additional information to modify risk

A

sometimes carrier risk from a pedigree can be reduced further in additional information is available, such as genetic test results, number of unaffected/affected offspring or a biochemical test.
Involves a calculation which modifies the initial probability of a person being a carrier by incorporating additional information

20
Q

Reducing CF carrier risk using a genetic test

A

simple test - CFTR-OLA can test for 90% of CFTR mutations in the Northern European population
reduced CF carrier risk from 1/25 to 1/241

21
Q

what can pedigrees show?

A

genotype or phenotype as genotype are not always available

22
Q

what is a Punnet square used for?

A

used to predict the genotype of a couple’s offspring
if someone is clinically unaffected this can be ruled out of the options so there are 3 possible remaining genotypes so the result will be out of 3