More Complex forms of heredity and pedigrees

Daily Question for today went something like this

A male and female who are NOT colorblind have a son who IS color blind. He marries a girl, they have 3 children (2 girls and a boy) all of which see normally. The son then has two kids, a boy and a girl. The BOY is color blind. Draw out a pedigree showing the inheritance of this trait. Then determine if this is a dominant or recessive trait.

First, I had you draw the pedigree with JUST the males/females and coloring in only the individuals we KNEW expressed the trait (WERE colorblind.) Based on that, most of you were able to tell me it had to be recessive since it showed up in the offspring of parents that did NOT express the trait.... ok... thats a start. THEN i filled in the rest of the pedigree and asked you - what is WRONG with this?!?! It looked something like this.....

So your FIRST question should be - WHY isn't the male heterozygous in the two cases where they had offspring that that DID express it but the mother IS? MISS Evrard!!! YOU MESSED UP.... This CAN'T be right?!?!?!?!

Well...... I am the first to admit I do often mess up... but in this case.... NOPE.... think harder................

WHAT could cause a recessive trait to show up more often in MALES than females?!?!?! It's as if there is no OTHER allele there to counter act it..... say like if I had only ONE of that chromosome.....

YUP - Not only was this a recessive trait - it was X-linked. It shows up more often in males because if they inherited it (from their mother) they don't have the advantage of having a second X that may contain the "good" allele from their dad since their dad is who gave them their Y chromosome.

After this we went on to predict the outcome of more x-linked scenarios and moved into other complex forms of inheritance. In the notes we have moved from polygenic inheritance (which we discussed yesterday) to Incomplete dominance. This led 2nd period into a pretty in depth discussion on eye color and then why some people have two different colored eyes..... 8th period... Hold on tight - we have a long period tomorrow so you will get there as well!!!