In this lab, we will be looking at Indian Corn that is the result of two parents. The parents were both Yy Ss. Y is yellow, y stands for white. The Yellow trait is dominant. S is smooth, s is shrunken. Smooth is dominant. Before we start, we need to list the possible gametes for the corn. We could have YS Ys yS ys. So, we need to do a Punnett square to determine what phenotypic ratios we would expect for the offspring of this match up.
Gametes YS Ys yS ys
YS YYSS
Ys
yS
ys
So, we need to fill out the Punnett square. If there is a dominant allele, then that is the trait that will be expressed phenotypically. For instanceYy, will be yellow. If there is no dominant allele, then the recessive trait will be expressed. For instance yy will be white.
Fill out the table and determine the ratio of Yellow Smooth, Yellow Shrunken, White Smooth, White Shrunken.
What is this ratio?
With the four possibilities of gametes from each parent, you have a total of 16 possible combinations.
Have you filled out the Punnett square? Divide the total of each phenotype by 16.
To determine the ratio of phenotypes, we need to fill out the Punnett square using the possible gametes: YS, Ys, yS, and ys.
Gametes YS Ys yS ys
YS YYSS YYsS YySS YySs
Ys YYsS YYss YySs Yyss
yS YySS YySs yySS yySs
ys YySs Yyss yySs yyss
Looking at the Punnett square, we can determine the phenotypes of the offspring:
Yellow Smooth (YYSS): 1
Yellow Shrunken (YYsS, YySS, YySs): 3
White Smooth (yySS): 1
White Shrunken (YYss, Yyss, yySs, yyss): 4
Therefore, the phenotypic ratio of Yellow Smooth to Yellow Shrunken to White Smooth to White Shrunken is 1:3:1:4.