I’m not the target of that post, Smeghead, but I wanted to say that I greatly appreciated the marbles-in-a-bag summary. I think that’s the clearest explanation I’ve ever seen of how traits get passed on in a more-or-less consistent rate through generations.
Kudos!
Cats too.
Wait, inguanodons and roosters are mammals?
Wait another second, there are igaunodons? Where do I get one?
Inguanodons are mammals: they’re Mafia bosses who got tossed in a shithole. Because they’re so pissed at this, inguanodons flip out and kill people all the time.
I found it slightly cryptic, since it seemingly ignores the idea every person has two copies of the gene rather than one. But in conjunction with the Wikipedia article I managed to figure it out.
Not at all. Each ball represents one allele. Each individual contributes two balls to the bag.
I don’t think this has been mentioned, but the gene for polydactyly has incomplete penetrance. That is to say, even if you have one copy of the dominant polydactyl gene, you might still not express the trait.
This is of some interest to me because my father was born with six fingers on his right hand*, but I was born with no supernumary digits.
*Ironically, he lost a finger in a wood shop accident. The extra finger was removed at birth, so he only has four fingers on that hand today.
Huh, if I’d been born with an extra finger, I’d want them to let me keep it as a spare.
Sorry, apparently I didn’t find it slightly cryptic.
:rolleyes:
I was just clarifying in case someone else was confused. Nothing personal.
Honestly I don’t see how it can be a DOMINANT trait…recessive maybe. But not dominant.
Nobody in my family (that I’m aware of) or in DH’s family (again, nobody he is aware of) have had extra digits, yet our son was born with what the doctors were calling a digit by technicality (it was a flap of skin about 1/8th of an inch wide by 1/8th inch long with a fleshy bit on the end that was complete with a bone inside and a fingernail which grew normally on the outside). So how is it that our kid had an extra digit?
I think that gets into what awldune was saying about incomplete penetrance. Real gene expression, and real biology in general, is messier than the simple binary dominant vs. recessive we like to talk about in freshman biology classes.
Yeah…see all of that when (whoosh!) right over the old noggin. Science was never one of my best subjects.
Think of having the gene giving you a tendency toward extra digits, rather than giving you extra digits. It greatly increases the chance, but it doesn’t always happen.
A couple of things:
Sometimes supernumary digits were(are?) removed at birth without the parents’ knowledge. In a case like your son’s (and my father’s), the scar is quite small and might be overlooked or mistaken for a birthmark/mole/wart by adulthood.
Also there is the “penetrance” issue as mentioned above. If my father has polydactyly and my mother does not carry the gene, then I had a 50% chance of receiving the gene. If I carry the gene and don’t express it (further 65% chance) I could pass that gene on to my child (50%) who would then have a 65% chance of presenting supernumary digits. So one would expect that roughly 1/3 of the descendants of a polydactyl would express polydactyly.
I should say all of this is a layman’s “As I understand it” and open to correction by someone who more about genetics.
1/3 of the immediate children, but it becomes less and less likely with each subsequent generation, since grandchildren, great-grandchildren, etc. have a much lower chance of getting that gene from that particular ancestor.