Chap 10 I dentifying the Genetic Basis for Human Disease

Question 1

Allels at loci on the same chromosome assort independantly if at least this event occurs

Answer 1

At least one crossover between them always occurs

Question 2

what is the ratio of NR : R genotypes 1 : 1 for syntenic loci

Answer 2

when they are sufficiently far apart that at least one recombination event occurs with every meiosis

Question 3

Frequency of recombination = 0

Answer 3

when two loci are so close together that no recombination events occur between them

Question 4

Detecting recombination events requires what two things?

Answer 4

Hetero zygosity and Knowledge of phase

parent must be heterozygous

Phase = coupling (cis) or repulsion (trans)

Question 5

opposite of independent assortment

Answer 5

Linkage

Question 6

recombination frquency ø must be at least ___ to be considered unlinked

Answer 6

0.5

Question 7

the product of various haplotypes follow directly from the allele frequencies

Answer 7

Linkage equalibrium (D=0)

when the opposite of this occurs allelles are said to be in linkage disequalibrium (D does not =0)

Question 8

LOD score (Z) considered firm edidence that two loci are linked

Answer 8

+3

=Ømax is statistically different from 0.5

best estimate of recombination frequency ømax between a marker locus and the disease locus

the smaller Ømax is the closer the disease locus is to the linker marker

Question 9

Study that is deseigned to find the presence of a particular allele at a locus at increased or decreased frquency in affected individuals in a case controled study

Answer 9

Association Study

Case control study: looking at patients and matching group of controls with and without the genetic marker of interest in a population

a= Patients with genetic marker

b= controls with genetic marker

c= patients without the genetic marker

d = controls without the egnetic marker

Disease odd ratio = ad/cb

OR = 1 = no association

OR differs from 1 = association with disease

Question 10

study designed to assess for the presence of a particular allelle at a locus at increased or decreased frequency in affected individuals

Cross sectional study

Answer 10

Association study

Cross sectional study: Random selection of individuals in the population with and without the particular allele of interest

Calculation of relative risk:

a= patients with genetic marker

b=controls wothout genetic marker

c= patients without genetic marker

d= controls without genetic marker

RR= a/a+b / c/c+d

RR=1= no association

RR differs from 1 = association with disease

Question 11

For rare diseases which is better to calculate in association studies.

OR or RR

Answer 11

For rare diseases were a

OR is a good approximation of RR

Question 12

Range at which one would expect OR or RR to fall 95% (or 99%) of the time; chance alone.

Answer 12

Confidence interval

Excludes 1 => OR or RR diviates significantly

null hypothesis of no association can be rejected

Question 13

How much does an association differ from what would be expected if there was no association

Answer 13

Significance

Question 14

Definition: the divergence from 1

Answer 14

Magnitude of association