Q:Codominant gene expression and halotype matching - najah

[ArchivalUser]

Can someone please explain to me how a sibling has a 25%, 50%, and 25% chance of having none, 1, and 2 haplotype match with another sibling in codominant gene expression. [Goljan chapter 3.II.B.1.a.(1)]

i tried figuring it out and i just don't get it. can some please explain it to me.

[ArchivalUser]

ok so here are the details from the chapter:

Chapter 3. Immunopathology
II. Major Histocompatibility Complex
B. Class I molecules
1. Encoded on three closely linked loci that are designated HLA-A, HLA-B, and HLA-C.
a. Genes are codominantly expressed, meaning that genes encoding these molecules from both parental chromosomes are expressed (i.e., HLA-A molecules from both the mother
and the father are produced; Fig. 4-2).
(1) In a family, the chance of a sibling having a 0-, 1-, or 2-haplotype HLA match with
another sibling is 25%, 50%, and 25%, respectively.
(2) Parents are a 1-haplotype match.

Figure: 4-2:
Chance of a sibling with haplotype A2B2C2D2/A4B4C4D4 having a 0-, 1-, or 2-haplotype match in a family in
which the father is haplotype A3B3C3D3/A4B4C4D4 and the mother is haplotype A1B1C1D1/A2B2C2D2. Note that there
is a 25% chance for a 2-haplotype match (A2B2C2D2/A4B4C4D4), a 25% chance for a 0-haplotype match (A1B1C1D1/
A3B3C3D3), and a 50% chance of a 1-haplotype match (A2B2C2D2/A3B3C3D3) or (A1B1C1D1/A4B4C4D4). Using a parent
as a transplant donor is considered a 1-haplotype match. An identical 2-haplotype match is rarely achieved owing
to crossing over between the individual loci during meiosis when homologous chromosomes align with each
other. (From Goljan EF: Star Series: Pathology, Philadelphia, Saunders, 1998, p 63, Fig. 4-2.)

[ArchivalUser]

I try to dissected in more simple way and hope it work for you.

You inherit 1 haplotype from each parent -> there are a total of 4 different haplotype combo from mom & dad.

*Basic rule in HLA inher*
You have a 25% chance of inheriting all HLA/same 2 haplotypes
As any 1 of yr siblings, you have a 25% or 1/4 chance of not inheriting any of the same HLA/none of The same haplotypes and you have a 50% or 1/2 chance of sharing I haplotype with your siblings. Therefore, you have a 1 in 4 chance of being an identical match with your siblings.

i.e.
one child inherit one, dad got ( 1, 3, 5 & 7, 9, 11) mom got ( 2, 4, 6 & 8, 10, 12) -> YOU* ( 1,3, 5 & 2, 4, 6)

Now 2 children the same inherit HLA again dad got ( 1, 3, 5 & 7, 9, 11) mom got ( 2, 4, 6 & 8, 10, 12) your bro (1,3 5 & 8, 10, 12) you* as part family & your sis (2, 4, 6 & 7, 9, 11) your other bro SAME AS you got(1, 3, 5 & 2, 4, 6) your other sis (7, 9, 11 & 8, 10, 12) as your set of 3 HLA/A,B DR haplotype.
So A, B, C DR and DQ Ag inherited from our parent “Haplotype” unit of inherit for HLA given infreqeint recombo btw HLA loci

That’s what Goli try to cross a biological child shares ONE haplotype w each parent and sibling can share 0/1 or 2 haplotype w their component HLA Ag.

Probability ( sum up)
- 0-hap match or 2hap match btw siblings -> 25%
- 1hap-> 50% sibling match

[ArchivalUser]

I understood the 25% but not the 50%. It was a cognition/english issue. thanks cardio and this question: https://books.google.com/books?id=ZM1bAw...&q&f=false

Here's how it works: lets make a punnett square
Mom [A1A2]xDad[A3A4]= Child with 25% chance of getting any one of 4 possibilities: A1A3, A1A4, A2A3 OR A2A4.

if i am A2A4:
1. What is the chance that my sibling is also A2A4 ie what is the chance that my sibling has the same 2 haplotypes as me? ANS: 25% [perfect match]

2. What is the chance that my sibling doesnt have any A2 haplotype nor any A4 haplotype? well that means they can only have A1A3 and prob of that is 25%. [no match]

3. What is the chance that my sibling has either A2 or A4 in common with me? prob of them having A2 but not A4 [ie prob of A2A3]=25% prob of them having A4 but not A2 [prob of A1A4] = 25%. there fore we add the two prob 25+25=50%. [half match. this is the point i didnt understand]