Question

in the pedigree that is shown, which represents irenes allele combination?
$x^hx^h$
$x^hx^h$
$x^hx^h$
$x^hy$

Explanation:

Step1: Analyze Pedigree and Inheritance

The pedigree involves X - linked inheritance (since alleles are on X and Y chromosomes). Parents of Fred, Jack, and Irene are \(X^{H}Y\) (father) and \(X^{H}X^{h}\) (mother). Irene is a female (circle), so her genotype is two X - chromosomes.

Step2: Determine Mother's and Father's Alleles

Mother's genotype: \(X^{H}X^{h}\), Father's genotype: \(X^{H}Y\). For a female offspring (Irene), she gets one X from father (\(X^{H}\)) and one X from mother (either \(X^{H}\) or \(X^{h}\)). But looking at the pedigree, Fred (male, affected - blue) has \(X^{h}Y\) (since he is affected, and gets Y from father and \(X^{h}\) from mother). Jack is \(X^{H}Y\) (unaffected). Irene is a female (unaffected, white circle). So she must have two dominant or one dominant and one recessive but not showing the trait. Since father gives \(X^{H}\) and mother can give \(X^{H}\) (because if mother gave \(X^{h}\), and father gave \(X^{H}\), the genotype would be \(X^{H}X^{h}\), but Irene is unaffected. Wait, no - let's re - check. The mother is \(X^{H}X^{h}\) (carrier, half - blue circle), father is \(X^{H}Y\) (unaffected, white square). For a female (Irene), possible genotypes: \(X^{H}X^{H}\) (from \(X^{H}\) (father) and \(X^{H}\) (mother)) or \(X^{H}X^{h}\) (from \(X^{H}\) (father) and \(X^{h}\) (mother)). But Irene is a white circle (unaffected). So her genotype should be \(X^{H}X^{H}\) because if she was \(X^{H}X^{h}\), she would be a carrier (like her mother, half - blue), but she is white. Also, \(X^{h}X^{h}\) would be affected (blue), and \(X^{h}Y\) is male. So Irene's genotype is \(X^{H}X^{H}\).

Answer:

\(X^{H}X^{H}\) (corresponding to the option \(X^{H}X^{H}\))