Is it true that your hair genes (those which control if you bald/when you go grey) only come from your mother’s side of the family? If so how is this possible?
Do some traits skip a generation? How is this possible? Links to informative sites welcome 
Im not a doctor but im pretty dang sure all traits are from both sides (mother and father) like the mother has half of one trait and the father has the other half. Im probabbly wrong on this one but im just tryin to help…
:::SIGH:::
I fail at everything
First, let’s cover traits skipping a generation. We’ll consider hair color, and assume (for simplicity) that the only hair colors are brown and blonde. Every person has two genes for hair color. If either one of them or both is a brown-hair gene, then the person will have brown hair, and if both are blonde-hair genes, then the person will have blonde hair. In biology jargon, we say that the gene for brown hair (let’s call it B) is dominant over the gene for blonde hair (call it b – notice the lowercase). Now, when two folks have a kid, for each trait, the child will have one gene from each parent, randomly selected. So, for instance, let’s say we have a man who comes from a long line of dark-haired folks on both sides, and is therefore BB – Both of his hair genes are for brown. (When both genes are the same, it’s called homozygous; when they’re different, it’s heterozygous. Hence, our man is a homozygous brown.) Now, he marries a blonde-haired woman, who, of necessity, is bb : Both of her genes are blonde, or she wouldn’t be blonde. They have a kid, who gets one of his father’s genes, randomly selcted, and one of his mother’s. Since both of Dad’s genes are the same, the kid will have a B gene from him. Similarly, he’ll get a b gene from his mom, so he’ll be Bb, and therefore, he’ll be brown haired, like his dad. Now, there’s another similar family, who has a girl that is also Bb. If the two kids marry and have kids of their own, there’s four different possibilities for their kids: Grandkid will have either a brown gene from each, a brown from Mom and a blonde from Dad, a blonde from Mom and a brown from Dad, or a blonde from each. In the first three cases, the grandchild will have brown hair, but in the fourth case, he’ll have blonde hair, even though neither parent has blonde hair. This is what we’re refering to when we say that a trait skips a generation-- Blonde hair skipped from the grandparents to the grandchild. Note that the gene itself didn’t skip a generation, it just wasn’t expressed.
On to sex-linked traits. I don’t know for certain if baldness and white hair are sex-linked, but let’s assume for the sake of argument that they are. Again, there’s two competing genes: We’ll call them H for keeping your hair into old age, and b for balding. Notice that I made the b lowercase, which indicates that it’s recessive to H. What makes these genes special, though, is that they’re on the X chromosone. Women have two X chromosones, but men have one X and one Y, which has very few genes on it. What this means is that if a woman has a baldness gene, she’ll probably still keep her hair, because her other gene is likely to be an H. Men, on the other hand, since we only have one X chromosone, only have one of those two genes, so if we’ve got a b gene, we’re guaranteed to have bald hair, because that’s the only gene we’ve got. Now let’s look at some examples again. A woman has the genotype Hb, which means that she carries the baldness gene but doesn’t show the trait (because she’s still got the dominant hair gene). Now, her and her husband have a son. The son got his X chromosone from his mother, and his (insignificant) Y chromosone from his dad. Depending on which chromosone he got from Mom, there’s a 50-50 chance that he got the one with the hair gene, and he’ll keep his hair, but there’s also a chance that he got the bald gene, and will go bald. Note that, for a boy, it doesn’t matter what gene the father had, since the boy gets the Y from Dad, which doesn’t have either the bald or the hair gene on it. Now suppose that the same couple has a girl-- Now it’s important what Dad is, because a girl will get an X chromosone from him. Let’s say that Dad has all his hair… His daughter, then, will get his H gene, and either her mother’s H gene or her b gene. Either way, since she has at least one H gene, she keeps her hair. If she gets the b gene from her mother, then some of her sons might be bald, but if she gets the H from her mother, then all of her sons will keep their hair. On the other hand, if Dad is bald, then Daughter will either have Hb, and keep her hair but sometimes pass on the gene for baldness, or she’ll be bb, and she’ll go bald herself. In this case, all of her sons are guaranteed to go bald, and all of her daughters will either carry the gene or be bald, depending on whether their father has hair or not. Notice that it’s a lot easier for a male to be bald, because he doesn’t have a spare gene.
As for your case, you need to look at your maternal grandfather, your maternal uncles, and if possible, your maternal grandmother’s father and brothers. If they all kept their hair, then chances are that your mother has two hair genes, and you’ll keep your hair, too. If your mother is bald, then you’re definitely going to go bald. If your grandfather is bald, then your mother definitely has a baldness gene, and you’ve got a 50-50 chance of inheriting it. If your grandfather has his hair, but some of your uncles don’t, then there’s a 50% chance that your mom has a baldness gene, and if she has it, a 50% chance that you’ll inherit it from her. Got that?
I think the short answer would probably be, “If you want to know whether a guy will go bald, look at his mother’s father, not his father’s father.”
Wow, great discourse, Chronos. You said:
Actually, baldness is autosomal (meaning everyone, male or female, has two copies of the gene). It’s sex-influenced, not sex-limited. Let me 'splain:
There are 2 alleles (or versions) of the gene, let’s call them B1 and B2. Lets say B1 codes for baldness and B2 codes for hair. What makes this confusing is that the B1 protein is influenced heavily be testosterone. So in men, B1 is dominant to B2. If you are B1/B1 or B1/B2, you’re bald. If you’re B2/B2, you’re not. Incidentally, as I see my own hair getting scarcer, I take pride in the fact that it has been proven that the more testosterone you have in your system, the more sever your baldness. Bald men are the only real men. Anyway, back to the topic…
OTOH, in women, B2 is dominant to B1. So a woman who is B2/B2 or B2/B1 will have normal amounts of hair. “But wait,” I hear you cry, “how come B1/B1 women aren’t bald?” They are, I answer. Well, sorta. Remember, it’s affected by testosterone, so “bald” women are far less bald than bald men. They typically get patches of thinning hair later in life, but you never see the infamous male chrome-dome. Oftentimes, these women will get wigs or some such, so it’s not seen in public that often, but they’re out there.
So, to answer the OP, the gene comes from both sides of the family, but it can hide in women, giving rise to all the various theories about how it’s passed.
One genetic trait I know too well is that of muscular dystrophy.
The gene is carried by the mother of the child and the disease affects male children. Female children carry the gene and can pass it on to their own offspring.
Or hemophilia. The mother is the carrier, on the X chromosome. She passes it on to her children about…50 percent, I believe. Her sons have a fifty/fifty chance of becoming a bleeder. Her daughters have a 50/50 chance of being carriers.
A hemophiliac male cannot pass it on to his sons, since it is on the X chromosome. All of his daughters, however, WILL be carriers.