In questions like this, the best thing to do is write an example
First of all you need to know that a heterozygous may contribute genotypically different alleles: SY Sy sY or sy
So, if you cross two heterozygotes:
<em>SY Sy sY sy</em>
<em>SY</em><em>SSYYSSYySsYYSsYy</em>
<em>Sy</em><em>SSYy</em><em /><em>SSyy</em><em /><em>SsYy</em><em /><em>Ssyy</em>
<em>sY</em><em>SsYY</em><em /><em>SsYy</em><em />ssYYssYy
<em>sy</em><em>SsYy</em><em /><em>Ssyy</em><em />ssYy<em>ssyy</em>
<em />
<em>-Well, you see that dominant for both trails are: SSYY, SSYy, SsYY or SsYy</em>
<em>If you count them there are </em><em>9 dominant for both trails</em>
<em>-Dominant for the the</em><em> first trait and recessive for the second </em><em>can be: SSyy or Ssyy</em>
<em>If you count them there are </em><em>3 of them</em>
<em>- In r</em>ecessive for the first trait and dominant for the second<em> we have two possibilites ssYY or ssYy</em>
<em>So, we see that again we have </em>3 cases
-<em> Finally, for recessive for both trails the only possibility is ssyy</em>
<em>We have just one case (the one is left in the chart)</em>
<em />
<em>You can write it like this: 9:3:3:1</em>
