Question

[bucket]

Two normally pigmented parents are heterozygous for albinism. If the parents had two children, the probability of one child being albino and one being normally pigmented would be:

[NE2000]

Let X = Child being albino

Pr(X) = 1/4 (punnet square)
Pr(X') = 3/4 (punnet square)

The events are independent

Therefore the probability of the intersect is 1/4 x 3/4 = 3/16

There are two possible combinations

Therefore I think the final probability is 6/16 = 3/8. Is that right?

[bucket]

Yeah, that's the answer. But how did you get from 3/16 to 6/16 ?

[bturville]

Because they could have pigmented then normal, or normal then pigmented. 2 combinations are possible, so the odds are doubled

[NE2000]

It's like in Methods:

2!/(1!1!) = no. of combinations

[Mikey123]

Weird why would they have this is bio?

What if someone doesn't do methods?

[BA22]

meh, i think some bio resources go over it, it's unlikely to be a question as you can't have a calculator in the exam

The answer is 3/16 anyway as we are only looking at phenotypes, so its just a standard independent event probability

[bucket]

DNA replication, it's semi conservative because the daughter DNA contains one strand of parental DNA yes?

[BA22]

yep

[bucket]

Sweet.
Uhm, do we need to know too much about DNA helicase? My book doesn't mention it ANYWHERE. :S

[bturville]

Just know what it does.

[Faraz]

This is how I memorized what DNA helicase and ligase do...

they have the zip effect on DNA strands therefore

Helicase = High to low (unzips)

Ligase = Low to high (zips)

workks for me 

[bucket]

Hey thats cool! I have another question about helicase lol, in my book it says that DNA is heated to 95 degrees to denature the molecules and hence separate them, so when would they use helicase? lol

[Faraz]

the temperature things only used during PCR (which breaks the weak hydrogen bonds), but in normal human cell the temp is at 37C so heat cant break the bonds therefore helicase comes in and does the job.

[bturville]

Helicase is used inside organisms, so that the body systems don't need to get to 95 degrees! Its an enzyme.

You can also remember that DNA is a double helix shape, so helicase unzips the helix. Ligase glues the backbone back together (lig being from latin: like ligaments, ligands etc.)