Question about HLAs and inheritance?

[Lannister]

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Sorry if I'm posting this in the wrong place, I wasn't sure if homework help is allowed on SDN. Please feel free to delete if I'm breaking the rules!

We were given this problem at the end of lecture today but we weren't given the answer. Most of us weren't really sure how to approach it so I'm not sure if my answer is correct.

The following are HLA-A and HLA-B types for a father, mother, and their first child.

Father: A4, A11, B3
Mother: A2, A11, B2, B6
Child #1: A4, A11, B2, B3

The parents have a second child. Which of the following is least likely to be an HLA type for the second child?

A. A11, B2, B3
B. A2, A11, B2, B3
C. A2, A11, B2, B3
D. A4, A11, B2, B3
E. A2, A11, B3, B6

My thinking was to look at the first kid and used that to determine what could be the possible haplotypes from each parent. So possible haplotypes from the father are:

A11, B3
A4, B3

For the mother:

A11, B2
Then I assumed that A2 and B6 might be a haplotype since the kid has neither of those.

So, based on those possible haplotypes, I picked B, because if the kid has A2 and A2 + B6 is a haplotype, you would also expect him to have B6.

I'm really not sure if that logic makes sense at all. I'd be super grateful if someone could help me out!

Edit: upon further consideration of the problem I have no effing clue what I'm talking about. Help.

 

[Cara Delevingne]

B and C are the same answers

The following are HLA-A and HLA-B types for a father, mother, and their first child.

Father: A4, A11, B3
Mother: A2, A11, B2, B6
Child #1: A4, A11, B2, B3

The parents have a second child. Which of the following is least likely to be an HLA type for the second child?

A. A11, B2, B3
B. A2, A11, B2, B3
C. A2, A11, B2, B3
D. A4, A11, B2, B3
E. A2, A11, B3, B6

 

[doyouhaveaflag]

Sorry if I'm posting this in the wrong place, I wasn't sure if homework help is allowed on SDN. Please feel free to delete if I'm breaking the rules!

We were given this problem at the end of lecture today but we weren't given the answer. Most of us weren't really sure how to approach it so I'm not sure if my answer is correct.

The following are HLA-A and HLA-B types for a father, mother, and their first child.

Father: A4, A11, B3
Mother: A2, A11, B2, B6
Child #1: A4, A11, B2, B3

The parents have a second child. Which of the following is least likely to be an HLA type for the second child?

A. A11, B2, B3
B. A2, A11, B2, B3
C. A2, A11, B2, B3
D. A4, A11, B2, B3
E. A2, A11, B3, B6

My thinking was to look at the first kid and used that to determine what could be the possible haplotypes from each parent. So possible haplotypes from the father are:

A11, B3
A4, B3

For the mother:

A11, B2
Then I assumed that A2 and B6 might be a haplotype since the kid has neither of those.

So, based on those possible haplotypes, I picked B, because if the kid has A2 and A2 + B6 is a haplotype, you would also expect him to have B6.

I'm really not sure if that logic makes sense at all. I'd be super grateful if someone could help me out!

Edit: upon further consideration of the problem I have no effing clue what I'm talking about. Help.

Are you sure these are the correct answer choices? I second the above poster's observation that B and C are the same. I also agree with your haplotype assignments. A, D, and E all make sense with no crossovers. B and C would both require a crossover and would therefore be less likely. Not sure why you got it wrong.

In fairness, I don't think whoever wrote the question knows HLA that well. There's no such thing as A4, B3, or B6. The numbering is shared between the A and B antigens, so there is A3 but no B3. Bw4 and Bw6 are special epitopes in which one or the other exists on every B antigen (except B46 and B73). It doesn't really matter for the purposes of the question though, I think you have the right concept that they're going for whether or not you can figure out what's traveling together as a haplotype.

 

[jse24]

We must be classmates 🙂

B is the correct answer (A2, A11, B2, B3)

First you have to realize that A4 had to have come from the father, since the mother doesn't have it. This means A4 B3 was the father's contribution. So his two haplotypes are:
A4B3
A11B3

This means the mother gave A11B2 (the only other option). So, her haplotypes are:
A11B2
A2B6

Now if you were to have a kid with the haplotype of option B, the father would've had to donate A11B3 (he doesn't have either of A2 or B2). This leaves the mother to donate A2B2, which isn't a haplotype that she has.

If you go through all of the others, you'll see that you can pretty easily figure out how each parent could donate one of their haplotypes to get each result. B is the only one that won't work.

If this is still tricky, just make a punnett square crossing the four haplotypes above, and look for which of the five answer options can't result from your square.

Hope this helps

In fairness, I don't think whoever wrote the question knows HLA that well. There's no such thing as A4, B3, or B6. The numbering is shared between the A and B antigens, so there is A3 but no B3. Bw4 and Bw6 are special epitopes in which one or the other exists on every B antigen (except B46 and B73). It doesn't really matter for the purposes of the question though, I think you have the right concept that they're going for whether or not you can figure out what's traveling together as a haplotype.

You're right, but it was my understanding that the naming was arbitrary for simplicity's sake, since the concept behind the question doesn't really change.

 

[doyouhaveaflag]

You're right, but it was my understanding that the naming was arbitrary for simplicity's sake, since the concept behind the question doesn't really change.

Totally agree it doesn't matter for the question, and I tried to convey that in the last sentence of my response. I just really like HLA and I was in a mood to be nitpicky this morning 🙂

What I think is really cool is that you do actually see a fair number of crossovers between A and B because they're not as close together as the class II genes. C actually sits between A and B but was discovered much later so didn't get named in order. So, it wouldn't be too surprising to see a kid with the type given in answer choice B in real life (crossover in mom to give A2_B2), it would just not be as common as the other answer choices.

 

[Smurfette]

Homework help is NOT allowed.

Closing thread.