Dihybrid cross

[reising1]

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Can anyone give me their technique for doing dihybrid crosses? Here is an example question:

Let's say I have two phenotypes, height and color. Let's say TT or Tt is tall and tt is short. And then for color, it can be red, white, or pink. RR is red, rr is white, and Rr is pink.

Let's say I cross
TTRr x Ttrr

How do I make the table for this? What is the general rule for making the table for dihybrid? I know that for normal crosses, like Hh and hh, it's a simple table with H and h on the top, and h and h on the left to produce Hh to hh in a 2:1 ratio.

 

[Deadlifts]

Can anyone give me their technique for doing dihybrid crosses? Here is an example question:

Let's say I have two phenotypes, height and color. Let's say TT or Tt is tall and tt is short. And then for color, it can be red, white, or pink. RR is red, rr is white, and Rr is pink.

Let's say I cross
TTRr x Ttrr

How do I make the table for this? What is the general rule for making the table for dihybrid? I know that for normal crosses, like Hh and hh, it's a simple table with H and h on the top, and h and h on the left to produce Hh to hh in a 2:1 ratio.

Punnett Squares for dihybrid crosses take longer because you have to make each maternal/paternal row gamete possibility. The one you gave doesn't have a 4x4 setup like a heterozygous cross would. Remember, you're filling the table out based on contributions from each parent's potential gamete.

TTRr makes gametes: TR, Tr
Ttrr makes gametes: Tr, tr
That's just a 2x2 box.

A self-cross of TtRr gives:

TR, tr, Tr, tR. You'd have a 4x4 square for a heterozygous cross. (SEE EXAMPLE: http://www.tangerinegecko.com/Genetics images/Dihybrid cross.jpg)

However, drawing out squares can get messy with 2 or 3 allele types. You should be able to multiply fractions to make it quicker.

TTRr x Ttrr

What's the proportion of offspring heterozygous for both alleles from this cross?

Tt: (1/2)
Rr: (1/2)

(1/2)*(1/2) = 1/4

The quicker you can be with proportions, the better imo. I honestly don't know if it would ever show up but I'd think it would be a fair question to see something like AaBBCcDDee as a self-cross just to see if you can do the math.

 

[reising1]

thanks