Thanks. I realized that sometimes we call anything anything to do with DNA "genetic", although the original term was about a unit of heritability, before DNA was known. But even if a mutation occurred, if that mutation was present in the sperm or egg, it would be inheritable, right? Unless something about the mutation rendered the sperm or egg incapble of fertilization, or normal development.
Caselbro,
I know that recessive genes play a role and lots of things like that. Also, there are very few cases where it's a simple, one gene, one trait correlation. Some diseases are like that, but that's not the usual case.
For example, I don't think there is one "tall" gene, but tall parents are more likely to have tall children. Some tall parents have short children. Some short parents have tall children, but from a probability standpoint, if your ancestors are tall, you are more likely to be tall.
If we measured the height of people, and found that there was absolutely no correlation between the height of the parents and the height of the child, we could conclude that height was not influenced by genetics, correct?
There is one exception I know of. If the carrier cannot express the gene, then there won't be a correlation between parent and child, but there will be a correlation between close relatives and children. The best example I know of is male pattern baldness. It's passed on the X chromosome, which you get from your mom. So, if your dad is bald, you are not likely to be bald. Meanwhile, your mom is not bald. So, there is no correlation between parental baldness and child baldness.
However, there is a correlation between baldness among relatives and child baldness. A common misconception is that you can look to your grandfather, your mom's father, to get a clue about baldness, but that isn't true. That isn't true because your grandfather could not pass his baldness gene to your mom. You have to look to your maternal uncle. If he was bald, then he got the gene from your grandmother. She might have also passed it to your mom, who might also have passed it to you. So it isn't a case that if your uncle was bald you will be bald, or if your uncle was not bald you will not be bald, but if your uncle was bald, then the probabilty you will be bald is higher than if your uncle did not go bald. Other male relatives on your mother's side might give weaker correlations.
So, more correctly, if there is no statistical correlation between family members with a particular condition, and children with a particular condition, then we can conclude that the condition is not caused by genetics. Conversely, if there is a correlation, then it either must be inherited genetically, unless there is a common environmental factor that the family members share. (i.e. if a family living on the uranium mine tends to have extra limbs, it doesn't necessarily mean that extra limbs are genetically inherited.)
