Like many stupid arguments in my life, this one was inspired by science-fiction/fantasy novels. Yes, I’m a geek, and everyone I know is a geek. Anyway, the question is, could there exist genetic traits that are passed down only from father to son? The example that spawned this debate was (fictional) inherited psychic ability, but it quickly expanded to encompass inherited traits in general.
I contend that it is not possible for a man to inherit a trait from his father that could not also be inherited by the man’s female siblings. The limit of my formal scientific training was Intro Bio, but as I understand it genetic abnormalities that express themselves only/primarily in men (such as color-blindness or hemophilia) are located on the X chromosone. Men inherit them from their mothers. Whether or not the father has the gene is irrelevant when it comes to his male offspring, since they don’t inherit their X chromosone from him. It’s relevant only when it comes to female offspring, who would need to inherit the trait from both parents.
My friend is convinced that there could be male-line only traits, although she is willing to admit that she can’t think of any real-life examples. She thinks that maybe a gene could be located only on the Y chromosone (something I don’t think is possible), or that a genetic trait might need to be “triggered” by high testosterone levels. That seems a bit more plausible to me, but I think such a trait could still express itself in women who had above-average testosterone levels.
So, what’s the Straight Dope? Is is possible for a genetic trait to be handed down only from father to son, like a biological last name, or is that idea mere fantasy?
Yeah, I agree with Mangeorge. Your question makes no sense. Have you ever heard of the “Y” chromosome on the last pair of chromosomes? I’d like to see a female sibling inherit that! Maybe you should rephrase your question? - Jinx
My dad’s prone to lipomas-- essentially fatty deposits under the skin. The more weight he puts on, the more he gets. Both of my overweight brothers have them as well, but my sister (who is equally overweight) does not.
I’m a normal-to-skinny guy, so I don’t have them either.
Of course, there’s always the chance that my sister and I aren’t my dad’s children, but I think that’s unlikely.
There are a few active genes on the Y chromosomes and these could be inherited only from father to son, since females do not get a Y chromosome. My daughter, who is a geneticist informs me that there is a gene called H-Y on the Y chromosome and it determines (ready for this), sex. Which is one trait that is very definitely passed only from father to son. But there are a (very) few others, although she didn’t know any offhand.
The original OP was more accurate than some are giving credit for. The above example could be caused by a trait being passed from the mother, but only expressed in the male line. If lipomas is caused by a recessive gene on the X chromosome, and the mother has a normal gene on one X and a lipomas gene on the other X, the mother will not suffer from lipomas. If the father’s X has a normal gene, then none of their daughters will have lipomas (but 50% will be carriers).
Each son has a 50% chance of getting lipomas depending on which of his mother’s X chromosomes he got. Hence the trait is passed from the mother.
This is, indeed, the most common way that sex-related genetic traits are passed - through the mother. A trait would pass through the father only if the gene causing the trait were found on the Y chromosome and not the X. There are not many such genes, as Hari S says.
Thank you, Hari and amarone. I suppose the answer to my question is that a male-line only trait is theoretically possible but would be very unusual.
mangeorge, penis size is not a male-line only trait. It is affected by both the mother and father’s genes, although it is obviously only expressed in male offspring. But if the maternal grandpa didn’t have a large penis then there’s no guarantee that Junior will, no matter how well-endowed his own father is.
Oh, and I meant “a male-line only trait is theoretically possible but would be very unusual” to mean “another, as-yet undiscovered male-line only trait is theoretically possible but would be very unusual”. Hope that makes a little more sense.
I was smacking myself over not seeing the forest for the trees and failing to realize that being a man itself is inherited from the father, but on second thought I don’t think that really is an example of what I was after since being a woman is also inherited from the father. That is, the sex of the baby is always determined by the father’s genetic contribution…except maybe in some of the rare cases where a person has some combination of chromosones other than XX or XY, but that’s getting beyond my limited grasp of genetics.
There is a (very rare and obscure) male-only trait other than maleness itself.
It’s a genetic quirk that causes excessive growth of hair on the ears. The gene lives on the Y chromosome and is therefore always passed from an affected father to all of his sons. If I recall correctly, it’s found in a few famlies in India or south-east Asia.
So yes, it’s possible, and it has happened, but since the Y chromosome is pretty small there isn’t a whole lot of room on it for genes other than those necessary to make boys into boys.
The Molecular and Cell Biology Pages at UCB include a lecture on pedigree analysis, where I read that
“A Y-linked trait would pass from an affected father to all of his sons, and then from them to their grandsons, etc. Besides the determination of maleness itself, no clearcut Y-linked traits have showed up, although genes controlling fertility, long ear hair, gonad cancers, and physical stature have been implicated as Y-linked traits. The Y has few genes and human females do perfectly well without it.”
I (Think) I inherited heard disease from my father. Mom and sister have no problems this way. Fortunately we have bypass surgery these days. Back in Dad’s day they didn’ t.
