Tough Genetics question, please help!

[raid517]

Hi can someone please help me to understand these questions? I'm completely stuck. Any help anyone can offer would be very much appreciated!

 

 

I'm a bit lost, but would probably be OK if someone explained it.

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To be clear I get (I think) that in the first question that the disease has to be recessive since neither of the parents are affected.

 

In the second question, if the disease is recessive this should give the numbers 1 and 2, 3 and 4, 10 and 11, since these all had offspring who were affected, but they weren't affected themselves.

 

in the 3rd question if I do a punnet square diagram, the genotypes produced from a cross between 10 and 11 could be:

Homozygous dominant: 1 out of 4, 25% chance or a probability of 0.25

Heterozygous: 2 out of 4, 50% chance or a probability of 0.5

Homozygous recessive: 1 out of 4, 25% chance or a probability of 0.25

 

Is this correct? I'm not sure about the last question, but this isn't relevant to what I'm doing anyway.

[CharonY]

Moved to homework. By shortly skimming the post it appears you are correct. Well done.

[Dak]

Is this correct? I'm not sure about the last question, but this isn't relevant to what I'm doing anyway.

 

Yes. Parents are Aa x Aa, hence there's a 0.5 chance of the offspring being Aa.

 

What weren't you sure about btw?

[Mr Skeptic]

Looks all correct.

[PopGen]

MWHAHAHAHAHA! You have all made the same mistake! The probability that individual 14 is heterozygous is actually 2/3. Since we know that this individual is not homozygous recessive, she must be either homozygous dominant or heterozygous. It is twice as likely that she will be heterozygous rather than homozygous dominant, hence there is a 2/3 chance she will be heterozygous.

[Dak]

lol, whoops, been too long since I've done this it would appear

 

You're right, there's a 1:2:1 chance BUT we can rule out the double-recessive (as you say), making it 2:1...

 

Sorry OP

[Mr Skeptic]

Hm, hadn't realized the OP answered a different question than was asked. He's correct about the probabilities of the offspring, but for a given offspring you have additional information.