Pedigree Chart Analysis (GF)

Finding probability for sequential events - multiply the probability for one sister by the probability for the next sister and so forth

Remember that the hemophilia gene is on the "X" chromosome. Alexis would contribute his "X" chromosome to his daughters. His wife, normal and not a carrier, would also contribute an "X" chromosome to their daughter. With two "X" chromosomes, a deleterious allele can be masked by an allele that isn't deleterious.

Remember that the hemophilia gene is on the X chromosome. Alexis would contribute a "Y" chromosome for his sons. Sons "X" chromosome would come from their mother who is normal (not a carrier).

Before modern-day drugs, she would probably have had difficulty surviving puberty when she began monthly menstruation. Modern day drugs can provide considerable assistance to those with hemophilia and improve their chances of living a relatively normal life.

If a male has the hemophilia gene on his "X" chromosome then it is expressed and he has hemophilia. William and Harry's squares are not shaded in on the pedigree chart so they don't have hemophilia.