Classic galactosemia is an inherited disease: The enzyme galactose-1-phosphate uridyltransferase has a defective gene. This enzyme is involved in the pathway that converts galactose, a simple sugar found in milk products, to glucose. Lactose is the main sugar in milk, and that sugar is made up of two simple sugars: galactose and glucose.
As you know, glucose is used by our cells to produce ATP as a product of cellular respiration, which is the usable form of energy for the human body.
In the normal metabolic pathway, we convert 1-phosphate-galactose into glucose, which we can use to make ATP for energy. In galactosemia, galactose builds up in the blood. When 1-phosphate-galactose builds up, severe liver, kidney, central nervous system, and other damage can occur. The disease is fatal if left untreated.
Scientists know the allele for normal digestion (G) is dominant, and the allele for galactosemia (g) is recessive. If a male who is heterozygous for the galactosemia trait and a female who has galactosemia have a child, describe how the disorder could be passed down. What are all the possible genotypes and phenotypes for the male’s parents.
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