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Dihybrid inheritance

You have been transported back in time into the body of Austrian monk Gregor Mendel. You have performed a cross between a pea plant heterozygous for both seed shape (S = smooth, s = wrinkled) and seed colour (Y = yellow, y = green) i.e. SsYy x SsYy.

 

What are your expected frequencies? The next table shows the possible crosses, colour coded for their phenotypic appearance.

Result of cross

	SY	Sy	sY	sy
SY	SSYY	SSYy	SsYY	SsYy
Sy	SSYy	SSyy	SsYy	Ssyy
sY	SsYY	SsYy	ssYY	ssYy
sy	SsYy	Ssyy	ssYy	ssyy

 

You found that your 160 daughter plants included the following:

Note: These data are in their “tallied” up form (see starting point).

 

Experimental data and expected frequencies

Appearance of the seeds	Observed frequencies	Expected frequencies
Smooth, yellow seeds	84	90
Smooth, green seeds	33	30
Wrinkled, yellow seeds	28	30
Wrinkled, green seeds	15	10