In a cross involving a heterozygous red flower plant (Rr) and a white flowered plant (rr), what is the probability that the offspring will be Rr?

This is a monohybrid cross between a heterozygous red-flowered plant (Rr) and a homozygous white-flowered plant (rr), where R (red) is dominant over r (white).

To find the probability of Rr offspring, set up a Punnett square:

The possible offspring genotypes are:

• Rr (heterozygous red) - 2 out of 4 offspring
• rr (homozygous white) - 2 out of 4 offspring

The probability of an offspring being Rr is therefore:

\[ \frac{2}{4} = \frac{1}{2} \]

This means there is a 50% chance that any given offspring from this cross will have the genotype Rr (heterozygous red). This type of cross is called a test cross, commonly used to determine the genotype of an organism showing a dominant phenotype. In a test cross of a heterozygous individual with a homozygous recessive individual, the offspring always appear in a 1:1 ratio of heterozygous dominant to homozygous recessive.