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To ask the second genetics question of the night?

(17 Posts)
StormyBlue Tue 13-Oct-15 18:30:52

The question re. eyes by another poster reminded me that I wanted to ask a this. As a disclaimer, I have only GCSE (+ read conflicting information on the internet) knowledge of genetics!

I have a DS and a DSS, half brothers. My OH has nearly black brown hair, I have brown hair, and so does his ex. Both boys have identical fluffy blonde hair, and DSS is nearly 9 so it's looking like it's permanent. Isn't brown supposed to be dominant? Does this mean that all three of us adults must carry a blonde recessive gene?

But then, OH has brown eyes, DSS has pale green and DS has dark greyish blue. I don't understand how he can have two kids with different eye colours and neither of them have brown eyes.


Oysterbabe Tue 13-Oct-15 18:38:19

You're right, you and DH carry recessive blonde hair, blue eyes genes.

Me624 Tue 13-Oct-15 19:19:30

Your ds's hair might still change. I was almost white blond until the age of about 11 or 12. It gradually got darker throughout my teens until it was brown. Then I hit the bottle so it's blond again :-)

RaspberryOverload Tue 13-Oct-15 19:25:13

My hair was fair when I was small, gradually going to a dark brown by late teen years.

My DBro started off white blond, gradually darkening to a much darker brown than I had.

This is common in my family.

MaidOfStars Tue 13-Oct-15 19:31:27

Very simplified....

Hair colour: all three parents carry one brown gene (dominant) and one blonde gene (recessive). They all have brown hair. However, in creating the two boys, each of them donated the blonde version, creating two boys who are both blonde/blonde.

For any child from 2 x brown/blonde parents, the chances of blonde/blonde are 1/4. Not very long odds at all.

Eye colour: exactly the same genetic relationship, but substituting eye colour for hair colour. You are all brown (dominant)/blue (recessive), all have brown eyes, any child from two of you has a 1/4 chance of being blue/blue.

x2boys Tue 13-Oct-15 20:59:06

I have blue eyes dh has brown eyes ds2 has brown eyes ds1 has green eyes as does dh dd from previous relationship her mother had brown eyesconfused

Mistigri Tue 13-Oct-15 21:46:00

My son has blue eyes - you have to go back three generations (his great grandparents) on both sides of the family to see where they come from. He also had white blond hair as a small child that has gradually darkened to light brown.

SwedishEdith Tue 13-Oct-15 21:51:58

Between blonde and red, which is dominant? I'm assuming blonde? But, I think it's much more complicated than that because things like strawberry blonde hair are really mixes of the two, aren't they?

leghoul Tue 13-Oct-15 21:53:06

Bb Bb
Bb Bb



leghoul Tue 13-Oct-15 22:02:45

You can work out your alleles (likeliest) by thinking of your and DH parents

If by brown you mean hazel, this is actually green and not dominant like brown. I was very surprised to learn blue is dominant vs hazel, (or 50:50 depending on alleles)
Mum is gg bb( hazel mother, blue eyed father, mum has hazel eyes), dad is bb bb(blue eyed mother blue eyed father)

3:3:3:1 ratio blue : hazel in children, or something like that....

leghoul Tue 13-Oct-15 22:07:27

Ipad typing not ideal for this. This if you just work out all possible combinations you'll see how likely it is

LunchpackOfNotreDame Tue 13-Oct-15 22:11:31

In a battle of blonde vs red it's usually red that wins.

With blonde mum brown dad usually you get a red offspring for some reason

HappyAsASandboy Tue 13-Oct-15 22:25:05

It's really not that simple, whatever A level biology might have taught us.

My DH and I both have pale blue eyes (so bb in school-biology terms). One of our children has dark brown eyes, the other two have light brown/slightly green sometimes eyes.

My step sister is a geneticist and says my DH can rest easy - eye colour is controlled by at least 6 genes, and any colour from any colour parents is entirely possible smile

MaidOfStars Tue 13-Oct-15 22:47:16

The redness of hair is controlled by a different gene than that controlling darkness of hair (from blonde to black).

Sandboy The National Genetics Reference database lists ten genes known to be involved in eye colour. They are not simply 'additive' effects either - their functions and interactions can be complicated.

colander1 Tue 13-Oct-15 22:55:27

Eye colour and hair colour are controlled by more than one gene, so it isn't that simple. Height for example is also controlled by many genes and these have an additive effect (the more dominant height genes you have the taller you are is the simplified version of this)

The problem with genetics is that to teach it you need to simplify it so rather than talking about single genes that are really single genes (eg production of enzymes etc) we pretend that things like hair colour and eye colour are controlled by a single gene.

Bogburglar99 Tue 13-Oct-15 23:07:05

I've always been intrigued that my mum has dark brown curly hair, my dad black. One of my brothers is black haired. The other two and me have an identical light brown/ dark mouse colour. Nowt like the originating parents but exactly the same as each other.

Two black haired friends also have three blond haired children who again look virtually indistinguishable from each other but not at all like their parents!

Skiptonlass Tue 13-Oct-15 23:40:43

There are multiple pairs of genes controlling eye, skin and hair colour.

On top of that, you can modify the expression of certain genes by having various genetic backgrounds..

Bottom line is its complex. smile

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