Question

the horticulturalist has an unknown geranium with an uncertain genetic makeup. she crosses it with a red geranium (rr) and gets a generation in which half of the plants have red flowers and half have white flowers. what does this combination of offspring tell her about the genetic makeup of the red geranium parent? the trait shows incomplete dominance. the unknown geranium is homozygous for red flowers (rr). the unknown geranium is homozygous for white flowers (rr). the unknown geranium is heterozygous for red flowers (rr).

Explanation:

Let's analyze each option:

• Incomplete dominance: In incomplete dominance, heterozygous individuals show an intermediate phenotype. Here, we have a simple dominant - recessive relationship (red and white), so this is not the case.
• Unknown geranium is RR: If the unknown geranium was RR (homozygous red), crossing with Rr (red) would give \(RR:Rr = 1:1\), all red - flowered plants. But we have white - flowered plants in the offspring, so this is incorrect.
• Unknown geranium is rr: If the unknown geranium is rr (homozygous white), crossing with Rr (red) gives \(Rr:rr=1:1\). Rr is red (assuming R is dominant) and rr is white. This matches the \(1:1\) red - to - white ratio in the offspring.
• Unknown geranium is Rr: If both parents were Rr, the offspring ratio would be \(RR:Rr:rr = 1:2:1\), a \(3:1\) red - to - white ratio (assuming R is dominant), which does not match the given \(1:1\) ratio.

Answer:

The unknown geranium is homozygous for white flowers (rr).