A test cross of an F1 individual with a double recessive parent resulted in a phenotypic ratio of $1:1:1:1$. This indicates that the F1 individual is:

Solution

1. A test cross involves crossing an individual with a homozygous recessive parent ($aabb$).
2. A ratio of $1:1:1:1$ implies four distinct gamete types produced in equal frequency.
3. This occurs when the F1 parent is heterozygous ($AaBb$) and genes assort independently.
4. Hence the answer is (B).