Final answer:
The risk of G6PD deficiency in Britney's current fetus can only be precisely determined if the sex of the fetus is known. Assuming Isaa does not carry the gene for G6PD deficiency, a male fetus would have a 50% chance of being affected, while a female fetus would not be affected.
Step-by-step explanation:
The question asks about the inheritance pattern of G6PD deficiency, which is an X-linked recessive disorder. Britney's full brother and two uncles have G6PD deficiency, indicating that their mother (Britney's maternal grandmother) was a carrier. Since G6PD deficiency is X-linked, Britney's mother, Lynne, has a 50% chance of being a carrier because she has one unaffected X chromosome from her father and a potentially affected X chromosome from her mother, a known carrier. Since Britney's mother has two brothers with the condition, she is a carrier. Therefore, Britney has a 50% chance of inheriting the affected X chromosome from her mother, making her a carrier as well.
Considering Britney's new partner, Isaa, we must assume he is not affected unless stated otherwise. If Britney is a carrier, there is a 50% chance the fetus could inherit the irregular X chromosome from her. However, since G6PD deficiency is more frequent in males (as males have only one X chromosome and no backup copy on a Y), the risk to the fetus is 50% if it is male. For female offspring, the risk is lower, as it requires two copies of the affected gene—one from each parent. Hence, the overall risk cannot be precisely determined without knowing the sex of the fetus, but we can calculate it based on possibilities: the child is either male or female.
If the fetus is male, the risk of G6PD deficiency is 1/2 or 50% because it can only inherit one X chromosome from Britney. If the fetus is female, the risk is 0% if we assume Isaa does not carry the deficiency. However, since we don't know the sex of the fetus, the risk is a combination of the two probabilities, driven by the 50% chance of being male or female.