Part B – Identify the mode of inheritance Look over the pedigree you constructed in Part…

Part B – Identify the mode of inheritance
Look over the pedigree you constructed in Part A.
Based on the inheritance pattern, which mode of inheritance must
be the cause of galactosemia?
Based on the inheritance pattern, which mode of inheritance must
be the cause of galactosemia?

sex-linked dominant

autosomal dominant

sex-linked recessive

autosomal recessive

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Part C – Predicting the probability of
inheritance
Jane and John are considering having another child. Given the
pedigree you constructed and the mode of inheritance for
galactosemia, what is the risk that their next child will have the
disorder?
Jane and John are considering having another child. Given the
pedigree you constructed and the mode of inheritance for
galactosemia, what is the risk that their next child will have the
disorder?

3/4 (because they are both heterozygotes)

0 (because they already have one child with the disorder)

1/16 (because they each have 1/4 chance of passing on the
allele)

1/4 (because they are both heterozygotes)

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Part D – Genetic testing
If Jane and John want to have another child, they plan to see a
genetic counselor to find out when it would be best to test for
galactosemia. A newborn with galactosemia must be put on a lactose-
and galactose-free diet as soon as possible after birth. Even on
this diet, affected individuals may still suffer from learning
disabilities, ovarian failure (in young women), late-onset
cataracts, and early death.
Which of the following tests would be most useful for Jane and
John to have?
Which of the following tests would be most useful for Jane and
John to have?

no testing

fetal chromosome analysis (examining fetal chromosomes for
abnormalities as early as 11 weeks into the pregnancy)

carrier screening of Jane and John (to identify whether either
or both of them carry the allele for galactosemia)

newborn screening (either assaying for the GALT enzyme or
measuring excess galactose in the newborn’s blood)

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