COMPLETED WITH THANKS genetics

[Comosus]

is it possible for a mother to have 1 dark haired, brown eyed child and 1 blonde haired, blue eyed child, with the same father
i seem to recall from biology class that because the brown eye gene is always dominant that it was impossible for a brown eyed parent to produce a blue eyed child - is this right?

Unfortunately it's often over simplified in biology (at low levels anyway).  There are quite a few different genes - 3 or 4 I think going from Brown to Hazel to Green to Blue to Grey.  Imagine those genes as very similar, almost identical, like a gradient of colour depending on your genes.  It's not simply that you have the brown gene or the blue gene at all.  For example, 2 green eyed people could have brown eyed children or blue eyed children.

Hair colour is also quite similar.  Imagine 3 genes coding for either dark or light.  3 dark ones and you'll have black hair.  3 light ones and you'll have blond.  Red hair is completely separate and is effectively a defect in a gene which then causes red pigment to build up.

Hair colour (not red hair though) and eye colour are linked.  This means that they are very close together on the same chromosome.  When I say that, I mean that one or some of the hair colour genes are linked to one of the eye colour genes, as the eye colour genes are on different chromosomes.  However I'm not quite sure where the hair colour genes are.  When the parental chromosomes come together the same chromosomes cross over each other and pieces of DNA are exchanged.  Because these genes are very close together, it's very unlikely that the cross will form between them, and so those 2 genes are likely to pass on together with eachother.

I did print off plenty of stuff on this but it's at home (I'm at uni now) so I don't have it with me, or the website addresses.

Essentially it's not as simple as one gene for hair colour and one gene for eye colour, there are several for each and they may or may not be scattered around on different chromosomes.

Andrew

[LizzieW]

We have one son who is very blond, (my husband always says he must be the milkman's!), but all our other children have very dark hair.  However, only one of them has dark brown eyes like I do, the others have greenish/greyish/blue coloured eyes.

Odder is the fact that both my parents had Rh.Positive blood groups, but I am Rh.Negative.  I was always told this wasn't possible, until I went to a lecture on blood groups and found out that it is, although rare.  Solution (!) came when my parents became blood donors and it turned out that both of them were positive to give and negative if receiving blood.  They had brown coloured blood group cards.

Liz

[Comosus]

We have one son who is very blond, (my husband always says he must be the milkman's!), but all our other children have very dark hair.  However, only one of them has dark brown eyes like I do, the others have greenish/greyish/blue coloured eyes.

Odder is the fact that both my parents had Rh.Positive blood groups, but I am Rh.Negative.  I was always told this wasn't possible, until I went to a lecture on blood groups and found out that it is, although rare.  Solution (!) came when my parents became blood donors and it turned out that both of them were positive to give and negative if receiving blood.  They had brown coloured blood group cards.

Liz

It's not as rare as you might think.  Take a look at the wikipedia article, in particularly the table: http://en.wikipedia.org/wiki/Rhesus_factor

It says there are 2 genes, 1 of which the choice is either R1 or r, for the other it's R2 or r.  So you're parents could have been R1r and R2r or both R1r or both R2r, which would give a 25% change of a child being rr.

There's also another type of blood group, MN.

[LizzieW]

Cosmosus

Glad you precised the wikepidia article!  I still think that over the population as a whole, the chances of having a blood group that is positive to give, but negative to receive must be fairly rare and for two people to meet who have the same type of blood group, even rarer.

I was a midwife for many years and can't recall seeing anyone with that type of blood group.

Liz

[MrsLizzy]

I always thought that any children of my partner and me would inherit his brown eyes and dark, handsome good looks!    I have blue eyes, my father has blue eyes and had golden blond hair (when he still had it!) and my mother has green eyes and light red-brown hair. 

[acceber]

So in a general sense, to what extent are characteristics likely to skip a generation? - (I apologise for that sounding like an essay question!)

e.g My mum looks facially a lot like her paternal grandmother when she was younger, however those same features were not present in my grandfather. Also my mum's first cousin has an uncanny resemblance to their great uncle (his mother's father's brother) but are not obviously present in his mother.

acceber