Galactosemia is a condition that affects how the body digests the sugar galactos
ID: 133560 • Letter: G
Question
Galactosemia is a condition that affects how the body digests the sugar galactose. The most common form of galactosemia, type I, is the most severe, and it results from mutations within the GALT gene, which encodes for an enzyme that processes galactose. Galactosemia is inherited in an autosomal recessive pattern. Imagine that your friend Mary has normal metabolism, but that her brother John has galactosemia. Mary and John's parents, Patricia and Les, are unaffected, although their maternal grandmother, Jean, also had the condition.?
a) If Patricia and Les have another child, what is the probability that they will have a daughter that is affected with galactosemia??
b) What is the probability that Mary and Justin will have an affected child?
Jean Patricia Les John Mary ustinExplanation / Answer
Please find the answers below:
Answer a) According to the information, the disease in inherited in autosomal recessive manner. This suggests that the presence of both alleles is required to be affected from the disease. Thus, John must be homozygous in nature. Thus, both of his parents, i.e. Patricia and Les must be carriers of the disease, hence heterozygous in nature. Thus, if Patricia and Les have another child, the probability of having a female child is always 50% of 1/2. The probability of being affected by the disease will be given as below:
Phenotype: Affected : carrier (normal) : non-carrier (normal) :: 1:2:1
This means that having an affected child has probability of only 25% or 1/4.
Thus, total probability of having an affected girl would be: 1/2 * 1/4 or 1/8 or 12.5%.
Answer b) According to the pedigree, Justin's uncle was affected from the disease, thus making 50% chances that Justin's father would be a carrier. This makes further 25% chances that Justin is a carrier. Finally, there are 50% chances that Mary is a carrier. Thus, the probability that Mary and Justin will have an affected child would be given by:
1/2 * 1/4 or 1/8 or 12.5%.
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