7.3 – Application: Practicing Pedigree Analysis

1. Gender Inclusive Pedigree Symbols
   Symbols:
2. 1. a square with an up arrow on the upper left corner
   2. circle with up arrow on the upper left side
   3. triangle with an up arrow on the upper left corner
   4. circle with a cross on the upper left corner
   5. square with a cross on the upper left corner
   6. triangle with a cross on the upper left corner
   7. circle with the letter i on the upper corner
   8. square with the letter i on the upper corner
   9. triangle with the letter i on the upper left corner

Check your answer in footnote^[1]

Determining modes of inheritance

2. 

   True or false?  In the pedigree shown (Fig. 7.4a), generation II shows a male with the trait with an affected son.  An X-linked trait cannot be passed from father to son. Therefore x-linked dominance can be ruled out as a mode of inheritance. This pedigree shows an autosomal dominant mode of inheritance.
   Check your answer in footnote^[2]

3. 

   The pedigree shown (Fig. 7.4b) tracks an X-linked recessive trait. As is typical of X-linked recessive traits, only males appear to be affected. Y-linked traits also only affect males. What feature(s) of this pedigree allow you to rule out Y-linked as a mode of inheritance in this pedigree?

   1. Y-linked traits pass from father to son, and fathers and sons always share the same phenotype.  In the X-linked pedigree shown in this figure, fathers who are affected by the trait have sons who are unaffected.  This rules out Y-linkage.
   2. Y-linked traits pass from father to son, and fathers and sons always share the same phenotype.  In the X-linked pedigree shown in this figure, fathers who are affected by the trait have sons who are unaffected.  This rules out X-linkage.
   3. Y-linked traits pass from father to son, and fathers and sons always share the same phenotype.  In the X-linked pedigree shown in this figure, fathers who are affected by the trait have daughters who are unaffected.  This rules out Y-linkage.

      Check your answer in footnote^[3]

4. Match the correct words to the blanks for the pedigree chart in Fig 7.4c:
   

   

   Words: affected, unaffected

   For a daughter to be [Blank a] by an X-linked recessive trait, she must inherit the X-linked allele from both her father and mother.  Her hemizygous father must also be [Blank b] by the trait if he carries the allele.  In this pedigree, we see an [Blank c] daughter of an [Blank d] father, which rules out an X-linked recessive mode of inheritance.
   Check your answer in footnote^[4]

5. Why are the offspring of consanguineous matings at higher risk for rare genetic disorders?
   1. Rare recessive disorders are uncommon because the causative alleles are uncommon among the larger population.  However, everyone likely carries at least a few rare, disease-associated alleles.
   2. When choosing a partner randomly, it is unlikely (but not impossible) that the partner will share the same set of rare, disease associated alleles.
   3. Close relations may share the same disease-associated alleles, making it more likely for offspring of a consanguineous relationship to inherit two disease-associated alleles of the same gene
      Check your answer in footnote^[5]
6. Match the words to the correct blanks, according to the pedigree chart in Fig. 7.4d.
   

   

   Words: II-1, aa, Aa

   Individuals I-1 and I-2 must both have genotype [Blank a]*Aa*, since they have an affected child (II-1) who is presumed to have genotype [Blank b]*aa*. This is also true for individual I-3, who has a child with the trait as well. I-4 has the genotype [Blank c]*aa*, since they have the trait.
   Check your answer in footnote^[6]

7. Since this is a rare trait in the population, in generation II, we assume that individual II-3 is not a carrier. If this is the case, what is the genotype of II-3? (See Fig. 7.4d)
   1. AA
   2. Aa
   3. aa
      Check your answer in footnote^[7]
8. True or false? Individuals II-4 and II-5 in Fig. 7.4.d must have genotype AA since they are unaffected (click image to enlarge).
   Check your answer in footnote^[8]
9. If the final offspring (see Fig. 7.4d) is affected and exhibits the trait, individual II-2 must be a carrier of the recessive allele “a” since individual II-3 was determined to be AA. What is the probability that they inherited the “a” allele?
   1. 1/4
   2. 3/4
   3. 2/3
   4. 1/3
      Check your answer in footnote^[9]
10. Match the words to the correct blanks according to the pedigree chart in Fig. 7.4d.
    Words: 3/4, aa, 1/4
    Assume individuals III-1 and III-2 have parents with the same genotypes. In each of these parental pairs, one parent is homozygous AA and the other is heterozygous ([Blank a]). The probability that III-1 and III-2 will be unaffected carriers (genotype As) is [Blank b]*.
    Check your answer in footnote^[10]
11. What is the probability that the offspring of III-1 and III-2 is affected (see Fig. 7.4d). Hint: Both parents are heterozygous.
    2. 3/4
    3. 1/2
    4. 1/4
       Check your answer in footnote^[11]