If you did not know whether brown or yellow alleles were dominant in corn, how could you tell with reasonable certainty? If you used a punette square to find out which one is dominant, how would you know which letters to use for each parent to figure out the F1 generation?

Answer 1

If the two genes are in the same allele, both parents are heterozygous, and the genes are either dominant or recessive, then about 25% of F1 generation will show recessive phenotype and 75% will show the dominant phenotype.

Homozygous = BB or YY

Heterozygous = BY

Once you find out which is dominant and which is recessive, use a lower case letter to indicate the recessive gene.