Below is a pedigree for an inherited lung disease. Provide the genotypes of each of the
individuals marked with lower case letters.
a) aa
b) Aa
c) Aa
d) A? (in other words AA or Aa)
Below is a pedigree for an inherited LUNG disease. Provide the genotypes of each of the
individuals marked with lower case letters.
a) Aa
b) Aa
c) aa
d) aa
e) A? (in other words AA or Aa)
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Below is a pedigree for an inherited heart disease. What is the probability that their child F
would have the inherited heart disease?
ANSWER: 50%
The adjacent pedigree is of a family with haemophilia as shown in Fig.9.4 . If the gene
for haemophilia is represented by Xh and the normal allele by X', write the genotypes of
each individual in the pedigree. If the genotype cannot be determined with certainty
write the possible alternatives.
Answer:
Begin with affected individual, III:3 . His genotypes is Xh Y. Similarly, his
affected uncle II: 5 must have the same genotor.Because of the family history,
his mother II:3 is an obligate carrier with genotype Xh X'. His father (II:4)
must be X' Y.
II:1 – X'Y (unaffected); II:2 and II:6 are X' X'
III:1 - X'Y (unaffected); III:2 - X' X' ;
III:4 – could be either X' X' or Xh X' (carrier)
III:5 - X'Y (unaffected);
III:6 - Xh X' (obligate carrier because her father is affected)
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Explain, giving reasons, whether the following pedigrees are compatible with autosomal
dominant, autosomal recessive or X-linked dominant and X-linked recessive
inheritance. (Note that a pedigree may be compatible with more than one type of
inheritance.)
Answers:
a. This pedigree shows dominant inheritance because of linear
transmission from parent to offspring. It could be either autosomal
dominant or X-linked dominant
b. This is very similar to the above - autosomal dominant or X-linked
dominant inheritance
c. This pedigree is consistent with X-linked recessive
inheritance because:
i.
only males are affected,
ii.
transmission is always through a carrier female, and
there is no male to male transmission
Another possibility is autosomal dominant inheritance with decrased
penetrance, thus appearing to skip generations.
Examine the pedigree from a family with a genetic disease and answer the
questions below:
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a. Does this pedigree indicate autosomal dominant, recessive or sex-linked
type of inheritance? Give reasons for your choice.
Answer: This pedigree is consistent with autosomal dominnat inheritance
with reduced penetrance. X-linked inheritance is excluded because of male to
male transmission (II:1 to III:1).
b. Assuming that B and b are the normal and mutant alleles respectively, what
would be the genotypes of the individuals: II.1, II.2 and III.3 ?
Answer:
II:1 – Bb . This individual, athough unaffected by the diease is obviously
transmitting the disease
II:2 – bb . This individual is normal and unrelated to the affected family
III:3 – Bb. Affected individual.
c. Individual II.3 requested genetic counselling. What is the probability that
her child would be affected. Explain why.
Answer:
II:3 is obviously transmitting the disease although she is unaffected. The
chance that her children would be heterozygotes is 50%. However, only some
of these would be affected, depending on the penetrance. In the aggbove
pedigree, three out of five heterozygotes were affected, equal to 60%. This is
only a rough measure of the penetrance because of the small number of
individuals involved. Thus II:3 has a risk of 60% of 50% (=30%) that her
offspring would be affected, and 20% risk that her normal offspring are in
fact carriers of the abnormal gene.
SOME MORE PROBLEMS AT
https://www.msu.edu/course/zol/344/Elsea/Pedigrees/
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