What would be the F1 phenotypic dominant: recessive ratio for this set of genes?

I don't know what the F1 phenotypic ratio for dominant: recessive genes would be if both parents had recessive genes.





The cross is between "aa" and "aa".


Would the dominant:recessive ratio be 0:4?


I'm confused. Could someone please explain this to me?


Thanks : )|||Yes, since the F1 generation could only be "aa" then the ratio has to be 0:4. Well, unless there is some sort of mutation, but, you can't predict that. :P|||If you wish to put a zero in a phenotypic ratio then it would be 0:4, which can more easily be stated by just saying that 100% of F1 have the recessive phenotype.|||If both parents are homozygous recessive for a certain trait: aa X aa, then each parent will produce only recessive gametes.





i.e. The dad will give an "a". The mom will give an "a".





The progeny (childen) from this cross can ONLY be genotypically "aa". The phenotypic ratio for the F1 generation will be 1 (they will all show the "aa" phenotype).





If you are looking for a dominant : recessive ratio, then you are right, it would techinally be 0:4 recessive because there aren't any dominant alleles in the parent generation.