Pedigree Construction and Analysis

Question 1

what is important to document in a pedigree? (5)

Answer 1

• miscarriages
• dev delay/ID
• recurrent/unusual med problems
• ages of onset
• ethnic background
• ?consanguinity

Question 2

what is the order of siblings on a pedigree?

Answer 2

in birth order from left to right

Question 3

what is “vertical transmission”?

Answer 3

there is an affected person in every generation

Question 4

what are some characteristics of autosomal dominant pedigrees?

Answer 4

affected person in each generation
males:females about equal
male to male transmission seen

Question 5

what can be seen in a AD d/o with reduced penetrance?

Answer 5

can see a “non-expressing carrier” pass trait to offspring

Question 6

what is typical of AR pedigrees?

Answer 6

only one generation has affected individuals, parents both likely carriers

Question 7

what are the characteristics of X-linked recessive pedigrees?

Answer 7

no male to male transmission
all female offspring are carriers
every affected male has carrier mother

Question 8

what are the characteristics of x-linked dominant pedigrees?

Answer 8

all daughters effected

males die before birth

Question 9

for autosomal recessive d/o, what is the risk of a couple, who already have affected offspring, having another affected offspring?

Answer 9

25%

Question 10

for an x-linked recessive d/o, what is the chance that the daughter of an affected male will be a carrier?

Answer 10

100%

Question 11

what is the key assumption of Hardy-Weinberg equilibrium?

Answer 11

genetic variation in a population is constant

making it unrealistic

Question 12

what is a practical application of HW equilibrium?

Answer 12

used to predict carrier status in a specific population

Question 13

what information is needed to perform HW calculations?

Answer 13

incidence of the genetic trait

Question 14

what equation is used for AD d/o?

Answer 14

p^2 + 2pq + q^2 = 1
p^2 = unaffected homozygous
2pq = affected heterozygote
q^2 = affected homozygote

Question 15

what equation is used for AR d/o?

Answer 15

p^2 + 2pq + q^2 = 1
p^2 = unaffected homozygous
2pq = carrier
q^2 = affected homozygote

Question 16

what equation is used for XLR d/o in males?

Answer 16

p + q = 1
p = unaffected hemizygous
q= affected hemizygous

Question 17

what equation is used for XLR d/o in females?

Answer 17

p^2 + 2pq + q^2 = 1
p^2 = unaffected homozygous
2pq = carrier
q^2 = affected homozygote (rare)

Question 18

what factors affect pedigree analysis?

Answer 18

assortative mating- mating among similar individuals

consanguinity- mating among close relatives

Question 19

what are the effects of assortative mating and consanguinity?

Answer 19

increased proportion of homozygotes in the next generation and may expose abnormal recessive phenotypes, also increases risk for polygenic traits and defects

Question 20

what is the coefficient of relationship (R)?

Answer 20

proportion of genes that are shared

Question 21

what is the coefficient of inbreeding (F)?

Answer 21

probability that an individual has received both alleles of a pair from a single ancestor

Question 22

in pedigree analysis of consanguinity, what “chance” is represented y each arrow?

Answer 22

1/2 chance