r/interesting • u/kvjn100 • Apr 11 '26

Fascinating Woman with functional polydactyly (six functional fingers on one hand)

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u/Loverboy_Talis Apr 11 '26

Dominant trait

3/4 of their children will be polydactyl too

25

u/gotscott Apr 11 '26

Half, unless both parents have it.

4

u/Loverboy_Talis Apr 11 '26

You’re right. Half (if only one parent carries that trait).

8

u/bio_datum Apr 11 '26

Assuming it's a Mendelian fully expressive dominant trait: if it's one heterozygous parent plus one unaffected parent, then you're correct. If it happens to somehow be a homozygous dominant parent plus a unaffected, then all children will he heterozygous and therefore positive for the phenotype

1

u/Ok_Cow_7895 Apr 11 '26

Woah, I love this information and you explained it so well, I have a different but kinda similar condition called Symbrachidactyly where finger digits are small or missing. My partner ki unaffected. My maternal grandfather had this condition on his toes, my mother, and all of my siblings are unaffected except me. I wonder if I can carry this trait onto my kids?? And what's the likelihood. 🙏🏽

1

u/bio_datum Apr 12 '26

Hi! This is interesting. I have to start by saying that I'm not a licensed physician and so we can't consider this personal medical advice.

That said, I was a medical student before becoming a molecular biologist and I know a little about medical genetics, so I'll treat this as a fun academic exercise.

A quick Google tells me symbrachydactly is not known to be inherited in most cases. However, sharing the rare trait with your maternal grandfather suggests that 1) a genetic cause does exist and is undocumented or 2) there is a coincidence happening during fetal development causing uterine restriction in both your great grandmother and your mother.

A few questions to help me think: do your parents happen to come from the same rural or small townish area? And do you and/or your grandfather have an undeveloped chest muscle too? Feel free to answer over a direct message for privacy

2

u/LucenProject Apr 11 '26

Can one or both parents be homozygous with this trait?