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A cross is performed between a bird that is homozygous for red feathers and a bird that is homozygous for blue feathers. Purple offspring result due to incomplete dominance. Then, two of the purple offspring are crossed.

What proportion of the offspring from the second cross will be purple?

A. 1 in 4
B. 2 in 4
C. 3 in 4
D. 4 in 4



Answer :

GinnyAnswer
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

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