Day 38 - Genetics

Inspired in part by a posting on Zygote Daddy's blog (see sidebar) but also by a conversation K___ and I had a couple of nights ago.

I have green-grey eyes, my mother has blue eyes, my father blue-grey. K___ has brown, as do both her parents.

My understanding was that eye colour was determined by the pair of 'alleles'. An allele is combination of information from the parents for a particular characteristic - i.e. eye colour. This two alleles pairing is a gene and the displayed characteristic is a genotype. That is, although an individual may have two different alleles, one will be dominant and it is this one that is the Genotype. My understanding, based on the old Gregor Mendel pea plant experiments we studied a school is that some alleles are dominant over others and this is always the case. Here's the sequence of dominance, as I understood it:

Brown is dominant over all, Green is dominant over blue and blue is just the gene equivalent of a gimp.

Thus, K___ has two brown-eyed parents, has brown eyes and will pass on a brown (henceforth 'B') gene.

Therefore, I reasoned, since both her alleles are dominant to whatever I bring to the table, they will win out, and our children would have brown eyes. I was quite confident about this. Here's how my alleles work out:

I have one blue eyed parent, and one blue-grey and have green-grey. Oh bugger. Now it gets complicated. Okay, let's think about this. My two brothers both have blue eyes. Since blue (b) is recessive, both of my parents must have blue genes. I have green in mine, so one of my parents must have green (G). Plus there's grey. Which is really awkward since my model doesn't cope with grey. I'll call that 'x' for now.

Here's the possible combinations for two people with bG & bx and how that would play out according to my understanding of Mendelian genetics:

bb bx Gb Gx
Blue DK Green DK

DK is don't know. So, my brothers must either be bb or bx, on the assumption that x is recessive. If x were recessive to b, it must also be recessive to G since G is dominant to b. Make sense?

Now, since I do not have Green eyes, which would be a Gb combination and I do have green grey eyes, it seems natural to assume that I have Gx eyes. But that would mean that x has to have the same dominance as G called co-dominance.

At this point, I go and do a bit of reading up on eye colour). Brown will dominate all, green will dominate blue. But grey is a completely different cup of sick. We don't know where grey comes into it. We do know there are three separate pairs of alleles that control whether you get Green, blue or brown eyes, and it's no longer as simple as brown rules all, green over blue and blue sucks regardless. So virtually all of the above is redundant. It's so simplistic it's pointless.

Arrrrrrrrggggghhh! There was me thinking eyes were like pea plants!

I found a website linked from the previous article that can do a green, blue or brown prediction based on the eye colour genotype of both sets of parents, siblings and the happy couple themselves. Ours comes out as follows:

              My Mum       My Dad       K___'s Mum       K___'s Dad
             b            G            B                B

                      Me                           K____
                      G                            B

b Sib?                                                                G Sib?  B Sib?
Y                                                                     N       N

This gives the following results:

Alleles
      bbbb     bbGb     bbGG     Bbbb     BBbb     BbGb     BBGb     BbGG     BBGG
      10       16.6     6.6      20.0     0.0      33.3     0.0      13.3     0.0

Genotype
              Blue                     Green                      Brown
               10%                       23.3%                     66.6%

Although brown eyes are the clear winner, apparently it's not a clear cut as I had thought.

So, what colour eyes will our baby have? Probably brown...

...but maybe green...

...or blue.

Not forgetting grey, of course. They might be grey.

Or Hazel. I know I haven't mentioned it, but it's also possible.

I don't really know, do I?

(Note: My apologies to anyone on RSS feeds getting confused by multiple versions of my posts arriving. You may attribute this to my being both innumerate and illiterate...)