Learning Genetics

04 November 2015

Recitation today

Today I'm planning to go over the 6 most-missed questions from exam 3, and anything else you might have questions about.

See you at 2:30!

28 September 2015

Some advice

In my opinion, truly understanding the material in chapter 7 is critical for making sense of the rest of the course.

(It's not a coincidence that we spent two lectures covering chapter 7)

I strongly recommend reading the chapter very thoroughly, and taking extensive notes as you read. I assure you that it is worth your time, even if it takes 12 hours.

Important note on reading the textbook:

I remember a time, long ago, when I used to be excited about textbook chapters that had a lot of pictures, diagrams, figures, and such. It seemed like fewer pages of reading, because I figured I only really needed to pay attention to the actual text part of textbooks. Many of my classmates and I had a sort of selective blindness toward diagrams, pictures, tables, and everything set apart in its own little box. (I'm sure many of you are free of this affliction.)

Eventually I discovered that I had it completely backwards. Understanding the figures is the key to understanding the material. Especially in genetics. The main text in the textbook is also very important because it gives the context and information you need in order to interpret and understand the figures (...the text also holds any important details that they couldn't fit inside the figures or that they couldn't work out how to illustrate).

If you can't explain each figure in your own words, then you aren't done reading yet.

In three words:

Understand the figures!

22 September 2015

Exam 1...

I won't be able to give anyone their exam booklet today. I'll let you know when they will be available as soon as I hear back from the professors.

21 September 2015

2:30 recitation canceled today

The 2:30 recitation is canceled today (Monday, 21 September).

I apologize for the late notice.

16 September 2015

Pedigree problem...

Using this information:

Answer these questions:

The pedigree provided looks complicated and messy. But it's really just squishing together a pedigree for hemophilia and a pedigree for albinism. Personally I think it's silly and annoying to cram so much information into pedigrees this way, because they just end up looking confusing and are hard to follow.

So... the first thing I did was to make separate pedigrees!

One for hemophilia:

And one for albinism:

Next, I figured out the genotypes for the hemophilia pedigree. Remember: squares are males, and circles are females. Hemophilia is X-linked, so the genotype options won't be the same for males as they are for females (because males are hemizygous).

We were also told that hemophilia is a recessive disorder:

Figuring out the rest is like solving a puzzle (it actually reminds me of sudoku for some reason...). Clara got an H allele from her mom, and her dad only has a h, so Clara's genotype has to be Hh.

We don't have enough information to tell whether Clara's mom's genotype is HH or Hh.

Charles has a brother with genotype hY. He got the Y from his dad (because his mom doesn't have one), so he had to have gotten the h from his mom. So, Charles's mom's genotype has to be Hh.

We don't have enough information to tell whether Charles's sister's genotype is HH or Hh.

Now, genotypes for the albinism pedigree. Albinism is an autosomal (i.e., not sex-linked) recessive condition, so we can ignore sex for this part.

Blue shapes (circles and squares) have albinism, so they have to have the genotype aa.

Anyone with the genotype aa had to get one a from each parent

White shapes have to have at least one A

Clara, Charles, and Charles's brother could be AA or Aa

It'd be really nice to know the genotypes of Clara and Charles, but we can't be sure based on the pedigree. They each have a 2/3 probability of being heterozygous, and a 1/3 chance of being homozygous dominant. They can't be homozygous recessive because we already know they don't have albinism.

Probability:

What's the probability that Clara and Charles have a son with hemophilia?

For this part we only have to look at the hemophilia pedigree. The probability that they have a son with hemophilia is the probability that their child has the genotype hY

...which is 1/4.

What's the probability that Clara and Charles have a daughter with albinism?

That's the probability that they have a daughter with genotype aa. In order for Clara and Charles to have a child with that genotype, Clara and Charles must each have an a allele. The probability that Clara has an a allele is 2/3. The probability that Charles has an a allele is 2/3. So, the probability that Clara AND Charles have genotype Aa is (2/3) x (2/3) = 4/9. If both parents are heterozygous, then the probability of their child having the genotype aa is 1/4. So, the probability of Clara and Charles having a child with albinism is (4/9) x (1/4)= 1/9. Their child has a 1/2 chance of being a girl, so the probability that they have a girl with albinism is (1/9) x (1/2) = 1/18.