Dihybrid Crossing

Agenda

1) Hand in Face Lab UP 25-28

2) Quiz on 11.1 and 11.2

3) Dihybrid crosses and Probability

4) Begin Homework

Homework

1) Finish UP 33-35

2) Read 11.3 w/ Cornell Notes

-Both due tomorrow

We first took a brief quiz on sections 11.1 and 11.2 (which most people thought was pretty easy) but some people were asking, “What are Dihybrids?” And so Mrs. Stein introduced us to dihybrids but first we took some notes on probability and dihybrid crosses.

Probability Notes:

Probability

*Definition-The likelihood that a particular event will occur.

-used to predict outcomes

Expected vs. Observed

*Expected – The mathematical outcome you predict based on a Punnett Square

*Observed- The actual results

-The deviation between them (expected and observed) is smaller with a greater number of traits.

Dihybrid Crosses

-Two trait crosses uses 2 sets of alleles from both parents

-Same steps except determining parental gametes is more complex

Then we did an example on the white board.

Ex. R-Round r-wrinkled

Y- Yellow y-green

(Heterozygous for both traits) x (Homozygous recessive for both traits)

RrYy x rryy

FOIL - (First, Outside, Inside, Last)

RrYy –First-RY rryy- First-ry

-Outside- Ry -Outside-ry

-Inside- rY -Inside- ry

-Last- ry -Last- ry

Notice how the parental gamete on the right comes out with all the same alleles.

On a punnett square you can acutally skip the step of making all those ry alleles, you only need to keep one.

RrYy x rryy

	RY	Ry	rY	ry
ry	RrYy	Rryy	rrYy	rryy
ry	RrYy	Rryy	rrYy	rryy
ry	RrYy	Rryy	rrYy	rryy
ry	RrYy	Rryy	rrYy	rryy

*So instead of having all of 4 columns in your punnett square, you can get ride of the 3 columns on the right because they show the same thing and the Genotypes will all remain the same

Genotype Frequencies:

RrYy: 4 ( 25% )

Rryy: 4 ( 25% )

rrYy: 4 ( 25% )

rryy: 4 ( 25% )

After we took some notes, then Mrs. Stein gave us a coin-flip demonstration. She asked us that if we were to flip one coin 4 times, what is the chance of them all landing on heads. The answer was 1/16. The reason it was 1/16 of a chance and not ½ is because you’re not only flipping the coin once, but 4 times. So you multiply once chance (½) by the number of times you are flipping the coin. So that would be - ½ x ½ x ½ x ½ = 1/16.

Then she asked us another question involving one member of the audience. She asked if anyone had 4 siblings including themselves with the same gender, and she chose Alecko and he’s one of the four boys in his family. Mrs. Stein asked what the chance would be if Alecko’s mom had another son. Now this time the answer was ½ because she only asked about the one new child. And it’s common sense to know that there are only 2 genders a baby can be.

After we were all done with that we had a few minutes to do our homework (UP 33-35).

And then the bell rang.

Our next scribe is Lucija.