Question

a horticulturalist wants to produce geraniums with specific characteristics. she knows that the trait of red flowers is governed by the allele r (rr and rr) and the trait of white flowers is governed by the allele r (rr). a cross of two geraniums yields offspring that are 100% rr. which choice best represents the alleles of the parents? ○ rr and rr ○ rr and rr ○ rr and rr ○ rr and rr

Explanation:

Step1: Analyze each option

• Option 1: \(Rr\times Rr\)

$$\begin{align*} Rr\times Rr&=(R\times R)+(R\times r)+(r\times R)+(r\times r)\\ &=RR + 2Rr+rr \end{align*}$$

Offspring genotypes: \(25\%\ RR\), \(50\%\ Rr\), \(25\%\ rr\).

• Option 2: \(RR\times Rr\)

$$\begin{align*} RR\times Rr&=(R\times R)+(R\times r)+(R\times R)+(R\times r)\\ &=2RR + 2Rr \end{align*}$$

Offspring genotypes: \(50\%\ RR\), \(50\%\ Rr\).

• Option 3: \(Rr\times rr\)

$$\begin{align*} Rr\times rr&=(R\times r)+(r\times r)+(r\times r)+(r\times r)\\ &=2Rr + 2rr \end{align*}$$

Offspring genotypes: \(50\%\ Rr\), \(50\%\ rr\).

• Option 4: \(RR\times rr\)

$$\begin{align*} RR\times rr&=(R\times r)+(R\times r)+(R\times r)+(R\times r)\\ &=4Rr \end{align*}$$

Offspring genotypes: \(100\%\ Rr\).

Answer:

\(RR\) and \(rr\) (Option 4)