help with biology questions?

1. The X and Y genes would have to be considered too. Let's say colour-blindness wasn't sex-linked i.e. autosomally inherited. Crossing BB against bb would result in all children having normal vision. Now add X and Y into the picture, with the mother being colour blind and the father having normal vision.

-----------X^b--------X^b------

X^B---X^BX^b-----X^BX^b--

Y------X^bY-------X^bY-----

The daughters would all have normal vision since the dominant allele is inherited from the dad. However, all the sons would be colour blind, since the X chromosome is only inherited from their colour blind mother.

So, you can see how the chances and ratios change.

2. It would depend on the genotype of the individual with the disorder. Since it's dominant, having one dominant allele would be enough to get the disorder i.e. DD or Dd (heterozygous). The homozygous recessive is dd. If the one with the disorder was DD, then ALL the offspring would get the disorder. If the parent with the disorder was Dd, then their offspring would have a 50% chance of getting it. Just do a simple Punnett Square. =)

3. All the male offspring would express the disease, because males can only inherit the X-chromosome from their mother (daughters inherit one from the mother and one from the father). If the mother was heterozygous then the sons would have a 50% chance.

Hope this helps clarify things. =)