heterozygous cross

These are the ratios for a typical heterozygous monohybrid cross.  For example, if Aa were crossed with Aa you would get the following gametic combinations: Aa, Aa, AA, aa.   Recall that phenotype is the expressed trait and genotype is the actual genetic composition.
For phenotypic ratios: Aa, Aa, AA all express the dominant trait
   ratio here is 3/4
And only aa expresses the recessive trait (because recessive alleles must be homozygous recessive be expressed).
   ratio here is 1/4
So the overall PHENOTYPIC ratio is 3:1
For genotypic ratio, we must look to see which alleles are the same and which differ:
   We have 2 Aa, 1 AA, and 1 aa
This is why the GENOTYPIC ratio is 1:2:1

**I really hope this helps!


Side note: memorize these ratios, they can help recognize future patterns in genetics.  I would also learn the ratios for a typical heterozygous dihybrid cross as well!

Thank you and I appreciate the tip about memorizing this.  Your explanation helps me a lot…

No problem.  I personally found genetics to be very intimidating when I took it, but once you get the hang of it the material really isn't all that bad!