Pedigrees
Peas are convenient subjects for genetic research, humans are not.
 Generation span is about 20 years
 Parents produce relatively few offspring
 Breeding experiments like Mendel’s (test crosses/self-pollination) are
impossible (or socially unacceptable) with humans.
o Unable to manipulate the mating patterns of people
Instead, geneticists must analyze the results of matings that have already occurred.
Information is collected by searching medical, historical, and family records and
assembled into a family tree describing the relationships of parents and children
and patterns of inheritance across the generations – the family pedigree.
A pedigree is a graphic representation of genetic inheritance. Pedigrees are useful in
tracing the passing of a particular genetic trait (gene) from generation to generation
as well as genetic diseases.
Hints for Solving Pedigrees
Autosomal Dominant:
- affected children always have an affected parent
- 2 affected parents can produce an unaffected child
- 2 unaffected parents will not have affected children
- Both males and females are affected with equal frequency
Autosomal Recessive:
- most affected children have normal parents
- 2 affected parents will always have affected children
- both males and females are affected with equal frequency
Sex-linked recessive:
- more males than females affected
- an affected son can have parents who are not affected
- an affected daughter must have a father who is affected and a mother who is
a carrier.
- The characteristic often skips a generation
- If a woman has the characteristic, all of her sons will have it
*Look at # of males vs. females and generations affected. If very few females are
affected it is likely sex linked.
**When it is ambiguous, choose the most likely pattern of inheritance: assume that
a genetic abnormality is rare. This means that very few people in a family will carry
the allele, and it is very rare that an individual who marries into the family carried
the allele.
http://www.genomics.health.wa.gov.au/education/fhh_howtocollect.cfm