Mendel: Punnett squares.?

Question

If the F1 generation of the cross between true-breeding plants with yellow (Y), wrinkled (s) seeds and green (y), smooth (S) seeds are crossed, what are genotypes of the offspring?

OUT OF 16
for example: 1/16 that it would be yyss

give probabilty for each combination of genes out of 16

Answer 1

F1 is the result of YYSS x yyss

ie YySs


F1 cross is YySs x YySs

and yields the dihybrid cross (see the wiki page for the punnett square)

YYSS___1/16
YYSs___2/16
YYss____1/16
YySS____2/16
YySs____4/16
Yyss____2/16
yySS____1/16
yySs____2/16
yyss____1/16

Hopefully that all adds up

Phenotypes is 9:3:3:1 ratio

Answer 2

You can most easily find the probability of genotypes this way.

F1 are YySs Separate the two genes involved to solve the problem mathematically instead of having to make a gigantic Punnett square.

F2 will be results of Yy x Yy and the results of Ss x Ss

1/4 YY: 2/4 Yy: 1/4 yy
1/4 SS: 2/4 Ss: 1/4 ss Multiply these two ratios together to get

1/16 YYSS, 2/16 (1/8) YySS , 1/16 yySS
2/16 (1/8) YYSs, 4/16 (1/4) YySs, 2/16 (1/8) yySs
1/16 YYss, 2/16 (1/8) Yyss, 1/16 yyss

That's how I'd do it.

Answer 3

Orinoco is exactly right. Try to learn this stuff...It's interesting so worth learning. Make a grid, and then count the 16 squares. It helps to use colored pencils to understand it,