Hi all!
This is quite late but here is my answer to this question.
I am looking forward to more challenging questions!! Hope everyone's prep for trials (and HSC) is going well
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It is difficult to determine whether the disease is dominant or recessive due to the patterns of inheritance demonstrated in the pedigree.
In a normal pattern of inheritance for a dominant disease, most of the offspring of the first generation of parents would have the disease. This is especially true for second generation males, if their mother has the disease, as they must inherit an X chromosome from her, and it is therefore a 50/50 chance of them also inheriting the disease if it was dominant.
It is also difficult to assume if the disease is dominant or recessive because generation 2, with an affected mother and unaffected father, produced an affected son and daughter. This means that either the disease is recessive and the father was carrier, meaning that the generation 3 son inherited an affected X chromosome from his mother, and the generation 3 daughter inherited an affected X chromosome from both her mother and father (fig 1), or the disease is dominant and both the son and daughter inherited a dominant disease affected X chromosome from their mother (fig 2).
As we do not know the genetic makeup of the female partner of the other male unaffected offspring in generation 2, we can not determine the reasons behind their children being unaffected and therefore if the disease is dominant or recessive. For example, if the female was or wasn’t a carrier for the recessive gene, as this would impact the children’s (generation 3’s) likelihood of inheriting the disease.
Therefore, without further information, it is difficult to determine whether the disease is dominant or recessive.