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? i. aa x aa ii. aa x aa iii. heterozygous x heterozygous iv. aa x aa v. homozygous dominant x heterozygous a) i, ii, iii, iv, and v only b) iii and iv only c) i and v only d) ii only

B) III and IV only

Explanation:

For IV

The genotype of crossing Aa x Aa gives you

AA, Aa, Aa, aa.

The genotype has:

1 homozygous dominant (AA)

2 heterozygous (Aa)

1 Homozygous recessive (aa)

leaving a genotype ratio of 1:2:1

The phenotype will have A for three of the children, since we have AA, Aa and Aa.

Since A is dominant the phenotype of the above mentioned will show 3 A and wil show 1 a since the is one child with aa and we know that a recessive gen only shows itself when it is on it's own.

Therefore the phenotype ratio is 3:1

For III

The same thing will happen the the way it is for IV.

This is because we are give Two heterozygous which I have already mentioned it means Aa.

So in simple form in II we are given:

Aa x Aa.

Which is the same as IV.

Thus our answer B

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