To determine the proportion of offspring that will be purple when two purple birds are crossed, we can use a Punnett square to analyze the genetic combinations.
1. Identify the alleles and their dominance:
- Let's denote "R" as the allele for red feathers.
- Let's denote "B" as the allele for blue feathers.
- Since the feathers show incomplete dominance, a bird with genotype "RB" will have purple feathers.
2. First Cross:
- A bird that is homozygous for red feathers would have the genotype "RR".
- A bird that is homozygous for blue feathers would have the genotype "BB".
- When these two birds are crossed, all offspring will have the genotype "RB" (purple feathers).
3. Second Cross:
- The two purple offspring from the first cross each have the genotype "RB".
- Setting up the Punnett square for RB x RB:
```
R | B
---------------------------------
R | RR | RB
---------------------------------
B | RB | BB
```
4. Analyze the results from the Punnett square:
- RR (Red) appears in 1 out of 4 boxes (1/4).
- RB (Purple) appears in 2 out of 4 boxes (2/4).
- BB (Blue) appears in 1 out of 4 boxes (1/4).
5. Determine the proportion of purple offspring:
- According to the Punnett square, 2 out of 4 offspring (2/4) will have the genotype RB and thus have purple feathers.
Therefore, the proportion of offspring from the second cross that will be purple is 2 in 4 or 0.5.
Hence, the correct answer is:
2 in 4
