Exam #4 Content

Question 1

Pedigree Analysis

Answer 1

Used to determine to mode of inheritance of traits in humans: most useful for rare conditions caused by single genes
- It is NOT POSSIBLE to set up controlled crosses and analyze large # of progeny in human genetics
- analysis of multiple generations in a single human family, genetic basis of specific traits and diseases can often be deduced

Question 2

Patterns of Inheritance in pedigrees

Answer 2

Commonly observed:
- autosomal recessive
- autosomal dominant
- x-linked recessive
Less Commonly observed
- x-linked dominant

Question 3

Mendelian ratios are rarely observed in families…

Answer 3

…b/c sample size is small

Question 4

Autosomal Recessive Inheritance

Answer 4

e.g: cystic fibrosis
- unaffected parents can have affected children
- traits appear equally in male and female
- all of the progeny from 2 affected parents should be affected
- traits can “skip” generations
- more likely to appear in consanguineous (“shared blood” aka: incest) unions
- if condition is rare in the general population unrelated mates are unlikely to be carriers

Question 5

Autosomal dominant inheritance

Answer 5

Traits appear in every generation, no “skipping”
- affected children have at least 1 affected parent
- traits appear equally in male and female
- two affected parents can produce unaffected children b/c they both can be heterozygous (unlike autosomal recessive)
- on average half the children of affected individuals show the trait if the other parent is unaffected

Question 6

X-Linked Recessive Inheritance

Answer 6

e.g: red green color blindness
- traits affect males more than females
- affected males typically have no affected offspring
- affected females will pass trait to all sons
- daughters of affected males are carriers (will pass trait to 50% of grandsons)
- sons of affected males do not receive the allele , do not show the trait and are not carriers

Question 7

X-linked dominant inheritance

Answer 7

e.g: fragile x-syndrome
- affected males pass condition to all daughters but not sons
- affected females pass condition to 50% of sons and daughters
- this inheritance pattern is rare

Question 8

Incomplete penetrance in pedigrees

Answer 8

For class purposes we will always assume 100% penetrance but…
- it it possible to encounter incomplete penetrance when observing real-life pedigrees
e.g: juvenile glaucoma