Pedigree Practice
The ability to tongue roll is a genetically inherited trait! Photo source
by Miss Baker
Click here for the answers to the pedigree practice problems. If you are having trouble downloading this file you will need to stop by the classroom tomorrow and check your answers.
Honors students: Go here to work on the more difficult problems. When you are attempting to answer these problems you must first answer the following questions:
a) Is this a sex-linked trait or a non-sex linked trait?
b) Is this a dominant trait or a recessive trait?
Please note that it will take a lot more time to answer these questions then your typical pedigree problems. It took me about 5 minutes per question and I have been doing this considerably longer than you have. So expect each question to take between 15-20 minutes. Good luck!
February 24th, 2008 at 9:15 pm
Miss Baker, I am still kind of confused (this is a little late to be figuring this out though.) I was trying to do the honors questions, but I got stuck on weather the particular trait was dominant or recessive, because when I tried it, it sort of tugged me in both directions. I guess I’m just doing it wrong. If you get this tonight would you please describe the first pedigree problem and tell me if it is sex linked and dominant or recessive? If you don’t get it I can just ask tomorrow. thanks:)
February 24th, 2008 at 9:59 pm
Danielle,
Here is my help for honors question #1.
The first thing you should notice is that females have the disorder. The only way a female can have a sex-linked recessive disorder is if her dad absolutely has the disorder and her mom is at least a carrier. You can see that this is not the case for the females who have this disorder.
Therefore, it is not sex-linked recessive. So the next question to ask would be is it sex-linked dominant? For this, look at the dad who has it (letter a). If it is sex-linked dominant, then all of his daughters would have the disorder! But, they don’t.
So, now we know it isn’t sex-linked. So, is it a dominant or recessive autosomal (body) trait? First, let’s hypothesize that it’s dominant. If it is dominant, the only way a child can get the disorder is if one of their parents has the disorder. But, you can see that one of the children that has the disorder (the one that is a sibling of letter d) has parents that do not have the disorder.
That rules out dominance. So the only thing left is autosomal recessive. When you make punnett squares to test the hypothesis that it is autosomal recessive, you find out that it works!