If John and Jane have another child, then what are the chances that they will have another child with hemophilia? If Jane becomes...

If John and Jane's son was born with hemophilia, the son
inherited this gene from his mother Jane. It is a sex-linked trait which means that it
is transmitted on the X chromosome. The son would inherit an X from his mother and a Y
from his father. Therefore, Jane passed the trait to the son. The Y chromosome doesn't
carry the hemophilia gene and plays no role in its transmission. Let us use the symbol X
for normal and X- to represent hemophilia gene. If you cross John who has no hemophilia
and thus his genes are XY with Jane, who is clearly a carrier and her genes are XX-(one
of her X's has the normal gene and one is carrying the hemophilia gene), then you get
the following results. For the girls, 50% are normal (XX) and 50% are carrier
females(XX-) . For the boys, 50% are male hemophiliacs, or (X-Y) and 50% are normal
males (XY). Since the hemophilia gene is recessive to normal, in females, they can be
carriers without actually inheriting the disease, since females possess two X
chromosomes. However, with males, since they only have one X chromosome, if they inherit
from their mother the hemophilia gene, then, they get the disease and if they inherit
the normal gene on the X chromosome, then, they are normal.