#x linked

[annexjournal]

X-linked Intellectual Disability (XLID) is an extremely heterogeneous disorder for which many of the causative genes are still unknown. So far, more than one hundred genes of the X chromosome have been found to be altered in males manifesting intellectual disability (ID).

the patient has a mild intellectual disability associated with attention deficit-hyperactivity disorder and a failure in memorization. He has no significant dysmorphism.

To view more at: http://goo.gl/SuxqAf

[muddledmeggie]

Male Pattern Baldness!

I asked you guys to ask me science things, and to my surprise a couple people did! Shane asked me my first question ever. I was really glad when I knew the answer too!  His question was:

"I've always heard that male pattern baldness is inherited through the mother, but if women don't get it how is it passed on?"

The genetics of male pattern baldness aren't completely known, but generally speaking this condition (called 'androgenic alopecia' if you want to get sciencey about it as I always do) is much more common in males, hence male pattern baldness. Like Shane heard, it is commonly inherited through the genes that the male receives from his mother. If the mother has all her hair though, how is she passing on something that makes her son bald?

Before going into the genetics of what gives someone male pattern baldness I am going to start with genetics 101! When a baby is conceived it receives one sex chromosome from the mother and one from the father. Females have two X chromosomes (XX) and males have one X chromosome and one Y chromosome (XY). Since females have two X chromosomes, during conception they automatically give an X chromosome to their child because that is all they have to give. The father however can randomly give the child either an X or a Y. Giving an X will create a female and giving a Y will create a male. This is why people say that the father determines the sex of the baby. 

Another important thing to know is that for the most part everyone has the same genes. What makes us different is that these genes have mutations in them that make us unique. Our DNA is like a book and the genes are the sentences making up that book. We all have the same sentences but with slightly different phrasing. A person without male pattern baldness may have a sentence in their book that says "I like canines" whereas a person with male pattern baldness has the same sentence reading "I like dogs". It's the same gene, but the slight change in it makes one person have the trait.

Male pattern baldness is what we call an X-linked trait. This means that the genes that cause male pattern baldness can be found on the X chromosome. Since women have two X chromosomes, they have two genes for male pattern baldness. Men only have one X chromosome, so they have one male pattern baldness gene. If a man has a mutation in his male pattern baldness gene that turns the word "canine" into "dog" he is going to develop male pattern baldness. A woman though has two chances because of her two X chromosomes. She can have one gene say "dog", but her second X chromosome could say "canine". This one "good" gene is enough to protect her from going bald. This doesn't change the fact that one of her chromosomes still says "dog" though, and when she reproduces there is a 50% chance that her child will get the "dog" chromosome. If that child also inherits a Y chromosome from his father, he will develop into a boy. The Y chromosome doesn't have any male pattern baldness gene. Since the boy only has one X chromosome, and the gene on it says "dog", no "canine" gene will be present to protect the boy, and the "dog" gene will dominate, leading to male pattern baldness. So just because the mother doesn't express the bald trait doesn't mean that she doesn't have the genes that can cause it.

If this same woman who carried the male pattern baldness gene had a child with a man with male pattern baldness, there would be a chance of them creating a daughter with baldness. If the child is a female, this means that the father had to pass on his single X chromosome, which has the "dog" gene because the father is bald. The mother has a 50% chance of passing on her "dog" gene too. If she did, both of the X chromosomes that their daughter inherited would have genes for male pattern baldness, and their daughter would inherit this trait. Luckily for women this condition tends to express itself differently in females, and usually causes thinning hair rather than the receding hair line. This hair thinning is called female pattern baldness. Remember though, if the woman donated the "canine" X chromosome, their daughter would have one "dog" gene and one "canine" gene, and this canine gene would be enough to protect her from expressing the condition. She would simply be known as a carrier, like her mother.

Colour blindness and two forms of muscular dystrophy are also X-linked!

I hope that wasn't too confusing and that my dog/canine talk didn't complicate things. Genetics is so cool you guys! If you ask me genetics questions, there is a greater chance that I will know the answer! If any of this was confusing and you want me to clarify, or if you have a question of your own, you can ask me here!