Question

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

Answer 1

B WOULD BE THE ANSWER NOT SURE THO SO DONT TRUST 

Answer 2

Answer:

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