Given three possible phenotypes for parents showing dominance aa , aa , aa which combination would produce a 1: 2: 1 ratio of genotypes and a 3: 1 ratio of phenotypes

A cross between two heterozygote individuals, Aa   x   Aa

Explanation:

A cross between two heterozygotes individuals would produce a 1:2:1 ratio of genotypes and a 3:1 ratio of phenotypes. This is a case of complete dominance of one of the alleles over the other one. In this case, the allele A completely dominates over the allele a.

The cross would be like:

Parental)       Aa     x     Aa

Gametes)    A     a         A     a

Punnet Square)

                        A          a

             A       AA       Aa

            a      Aa        aa  

The F1 genotype proportions are: 1/4 Homozygous dominant, AA

                                                        2/4 Heterozygous, Aa

                                                        1/4 Homozygous recessive, aa  

The F1 phenotype proportions are: 3/4 of individuals expressing the  

                                                           dominant trait.

                                                           1/4 of individuals expressing  

                                                            the recessive trait.

a- multicellular

b-eukaryotic

c-no cell wall

d-heterotrophic

e-autotrophic