Dihybrid cross worksheet - Free Printable

To solve this dihybrid cross problem, we need to determine the possible gametes for each parent and then fill in the Punnett square to find the offspring's genotypes and phenotypes.

Step 1: Determine the Gametes
Both parents have the genotype YyTt.
* Y = Yellow seeds (Dominant)
* y = Green seeds (Recessive)
* T = Tall plant (Dominant)
* t = Short plant (Recessive)

To find the gametes, we separate the alleles. Each gamete gets one letter for seed color and one letter for height. We can use the "FOIL" method (First, Outer, Inner, Last) on the genotype YyTt:
1. First: Y and T $\rightarrow$ YT
2. Outer: Y and t $\rightarrow$ Yt
3. Inner: y and T $\rightarrow$ yT
4. Last: y and t $\rightarrow$ yt

So, the four types of gametes for both the male and female parents are: YT, Yt, yT, yt.

Step 2: Fill in the Punnett Square
We place the male gametes across the top and the female gametes down the side. Then we combine them in each box.

| | YT | Yt | yT | yt |
| :--- | :---: | :---: | :---: | :---: |
| YT | YYTT | YYTt | YyTT | YyTt |
| Yt | YYTt | YYtt | YyTt | Yytt |
| yT | YyTT | YyTt | yyTT | yyTt |
| yt | YyTt | Yytt | yyTt | yytt |

Step 3: Determine the Phenotypes
Now we look at the traits produced by these genotypes:
* Yellow & Tall: Needs at least one Y and one T (Y_T_).
* Count: 9 squares (YYTT, YYTt, YyTT, YyTt...)
* Yellow & Short: Needs at least one Y and two t's (Y_tt).
* Count: 3 squares (YYtt, Yytt...)
* Green & Tall: Needs two y's and at least one T (yyT_).
* Count: 3 squares (yyTT, yyTt...)
* Green & Short: Needs two y's and two t's (yytt).
* Count: 1 square (yytt)

This results in the classic Mendelian ratio of 9:3:3:1.

Final Answer:
Gametes: YT, Yt, yT, yt

Punnett Square Genotypes:
Row 1: YYTT, YYTt, YyTT, YyTt
Row 2: YYTt, YYtt, YyTt, Yytt
Row 3: YyTT, YyTt, yyTT, yyTt
Row 4: YyTt, Yytt, yyTt, yytt

Phenotype of offspring:
* 9 Yellow seeds, Tall plants
* 3 Yellow seeds, Short plants
* 3 Green seeds, Tall plants
* 1 Green seeds, Short plant