Tag Archives: fruit flies

Completing Classic and Molecular Genetics on Khan Academy: Wings Sprint #1

This week for my Wings sprint I focused on genetics. I had lots of ideas of how I could learn more, but the one most available to me and the most fun seems to be Khan Academy; at least so far. I learned a lot this week! Here is all that I learned from different lessons. The paragraphs in quotes are what I put in the description of the card until I figured I wanted to explain things in detail.

Monday:

“I learned about sex-linkage, Thomas Hunt Morgan and his fruit flies, double cross-overs, and genetic mapping. I really enjoyed learning about Morgan and the fruit flies; it’s very interesting how the traits skipped generations and only showed up in the males. I think that would be a very interesting experiment to do myself! Maybe some other time I’ll do something like Mendel and his peas.”

Sex-Linkage: This was probably one of my favorite subjects. Bare with me: I need to explain quite a bit.

People usually have 46 chromosomes. 23 from your mom, and 23 from your dad. Each of your parents give you 22 non sex determining chromosomes, and 1 sex determining chromosome. Your mom can only give you an X because, of course, she will have XX chromosomes. Your dad can give you either an X or Y chromosome. If he gives you an X chromosome, your are a girl. If he gives you a Y, you are a boy.

Now that we have that covered, I can teach you about sex linkage. Have you ever heard about Hemophilia? It is a mutation in the X chromosome where the blood is unable to clot properly. Approx. 1 in 7000 men will have Hemophilia, and about 1 in 4,000,000 (million!) women. Why is this? The Hemophilia mutation is recessive, meaning that if there is a dominant trait it will be overridden. For example: A woman is a carrier for Hemophilia and has a baby with a man who has Hemophilia. That woman can either give the baby an X chromosome WITH the mutation or one without. The man can only give an X or a Y. Neither of them have the Hemophilia mutation. If the man gives the X chromosome to the child and the woman gives the child her mutated X chromosome, the girl will be a carrier. She can clot her blood without a problem, but could potentially have a Hemophilic child. But if the child was a boy, and the woman gave him a mutated X chromosome, he would have Hemophilia. This is because the Y chromosome can’t have the Hemophilia mutation and therefore can’t do anything to stop it. Men only need one X chromosome with the mutation, and women need both of their X chromosomes to have the mutation. The latter is highly improbable, resulting in practically no women having the mutation. And TA-DA! Sex-Linkage.

Thomas Hunt Morgan and his fruit flies: Thomas Hunt Morgan was an embryologist who had turned to research in heredity. In 1907 he began breeding the common fruit fly. He was hoping to discover large-scale mutations that would represent the emergence of new species. In 1910 he saw that one of the fruit flies had white eyes. He bred this mutant fly with a normal, red eyed female. The F1 generation were all normal. He then bred the F1 generation to produce F2 and one fourth of F2 had white eyes! One interesting thing about this is that only the males had white eyes; never the females. Here are some pictures to help explain it (from the Khan Academy article I learned about this from)

Screen Shot 2016-09-02 at 5.46.56 PM Screen Shot 2016-09-02 at 5.47.03 PM