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PEDIGREE ANALYSIS
Name: ______________________________
1. Why is it customary to use pedigrees to determine inheritance patterns in
humans? as opposed to conducting experiments like those by Mendel or
Morgan?
2. Read pages 166-167 in the text and note the characteristics that allow one to
make distinctions between the following modes of inheritance.
Autosomal Recessive
Autosomal Dominant
X-Linked Recessive
X-Linked Dominant
3. What are the various symbols used in a pedigree? Make an exhaustive key.
4. For the following pedigrees determine which mode of inheritance is most likely.
Label the mode of inheritance in the space provided, and then explain the
logic that you used to determine that it WAS one type of inheritance and NOT
another type of inheritance.
Similarly, once you have determined the mode of inheritance, label the
genotypes of as many individuals that you know for sure using the R and r
alleles. It is important to note that if you don’t know the genotype with
certainty don’t label it with the most probable (you can label one R_). Also, if
it is x-lined then the possible alleles will be XR, Xr, Y.
A. _______________________________
B. _______________________________
C. _______________________________
D. _______________________________
E. _______________________________
5. For each of the following modes of inheritance, state whether you can find
evidence in the pedigree against that mode of inheritance. Give reasons.
Assume that the disease is rare and that there is complete expressivity and
penetrance.
(i) autosomal
recessive
(ii) autosomal
dominant
(iii) X-linked
recessive
(iv) X-linked
dominant
(v) Y-linked
(vi) sexinfluenced
(vii) sex-limited
1.
a. Deduce the inheritance of this condition, stating your reasons.
b. If individuals 1 and 2 marry, what is the probability that their first child
will have the kidney disease?
30. The accompanying pedigree shows the pattern of transmission of two rare
human phenotypes: cataract and pituitary dwarfism. Family members with
cataract are shown with a solid left half of the symbol; those with pituitary
dwarfism are indicated by a solid right half.
a. What is the most likely mode of inheritance of each of these phenotypes? Explain.
b. List the genotypes of all members in generation III as far as possible.
c. If a hypothetical mating took place between IV-1 and IV-5, what is the probability
of the first child's being a dwarf with cataracts? A phenotypically normal child?
The accompanying pedigree concerns a certain rare disease that is
incapacitating but not fatal.
a. Determine the most likely mode of inheritance of this disease.
b. Write the genotype of each family member according to your proposed
mode of inheritance.
c. If you were this family's doctor, how would you advise the three couples
in the third generation about the likelihood of having an affected child?
Assume that this pedigree is straightforward, with no complications such as
illegitimacy.
Phenotype W, found in the individuals represented by the shaded symbols, is
rare in the general population. Which of the following patterns of transmission for
W are consistent with this pedigree? Which are excluded?
a. autosomal recessive
b. autosomal dominant
c. X-linked recessive
d. X-linked dominant
e. Y linked
The pedigree below is for a rare human disease called spastic paraplegia, a
nervous disorder in which there is an inability to coordinate voluntary
movements.
a. What mode of inheritance is suggested by this pedigree?
b. Which family members must be heterozygous according to your model?
(Pedigree from V. A. McKusick, On the Chromosomes of Man. Copyright © 1964
by American Institute of Biological Science, Washington, D.C.)
See answer
52. The pedigree above shows the inheritance of a rare human disease. Is the
pattern best explained as being caused by an X-linked recessive allele or by
an autosomal dominant allele with expression limited to males?
A certain type of deafness in humans is inherited as an X-linked recessive. A
man who suffers from this type of deafness marries a normal woman, and they
are expecting a child. They find out that they are distantly related. Part of the
family tree follows.
How would you advise the parents about the probability of their child being a deaf
boy, a deaf girl, a normal boy, or a normal girl? Be sure to state any assumptions
that you make.