Calculating the Proportion of Purple Offspring

Oct 13, 2025 by miodeya.com 55 views

Incomplete dominance is a phenomenon in genetics where one allele does not completely dominate the other allele, resulting in a combination of the two alleles. This leads to a new trait that is different from both parents. In the case of feathers, incomplete dominance can result in purple offspring when two different colored parents are crossed.

The First Cross: Producing Purple Offspring

Let's consider a scenario where two parents, one with red feathers and the other with blue feathers, are crossed. The red parent has the allele R for red feathers, while the blue parent has the allele B for blue feathers. When these two alleles are combined, they result in a new allele, P, which represents the purple color. This is an example of incomplete dominance, where the P allele is a combination of the R and B alleles.

The Punnett square for this cross is as follows:

	B
R	BP
P	PB

In this Punnett square, the BP and PB represent the two possible genotypes of the offspring, which will have purple feathers. The probability of each genotype is 25%, resulting in a 50% chance of purple offspring.

The Second Cross: Crossing Two Purple Offspring

Now, let's consider the scenario where two purple offspring from the first cross are crossed. Each of these offspring has the genotype BP or PB, which means they have one allele for red feathers (R) and one allele for blue feathers (B). When these two alleles are combined, they result in the P allele, which represents the purple color.

The Punnett square for this cross is as follows:

	B
R	BR
P	BP

In this Punnett square, the BR and BP represent the two possible genotypes of the offspring. The BR genotype has one allele for red feathers (R) and one allele for blue feathers (B), resulting in a red color. The BP genotype has one allele for red feathers (R) and one allele for blue feathers (B), resulting in a purple color.

Calculating the Proportion of Purple Offspring

To calculate the proportion of purple offspring, we need to consider the possible genotypes of the offspring. The BR genotype has a 50% chance of being red, while the BP genotype has a 50% chance of being purple. Since the BP genotype is the only one that will result in purple offspring, the proportion of purple offspring is 50%.

However, we need to consider the fact that the BP genotype can result in either a purple or a red color, depending on the combination of alleles. Since the BP genotype has a 50% chance of being purple, the proportion of purple offspring is 50% of 50%, which is 25%.

Conclusion

In conclusion, when two purple offspring from the first cross are crossed, the proportion of purple offspring is 25%. This is because the BP genotype has a 50% chance of being purple, and the BR genotype has a 50% chance of being red.

Answer

Q&A: Incomplete Dominance and Its Impact on Offspring

Q: What is incomplete dominance?

A: Incomplete dominance is a phenomenon in genetics where one allele does not completely dominate the other allele, resulting in a combination of the two alleles. This leads to a new trait that is different from both parents.

Q: What is an example of incomplete dominance?

A: An example of incomplete dominance is the combination of the alleles for red and blue feathers, resulting in purple feathers. When two parents with red and blue feathers are crossed, the offspring will have purple feathers.

Q: What is the Punnett square for the first cross between a red and a blue parent?

A: The Punnett square for the first cross between a red and a blue parent is as follows:

	B
R	BP
P	PB

Q: What is the probability of each genotype in the first cross?

A: The probability of each genotype in the first cross is 25%, resulting in a 50% chance of purple offspring.

Q: What is the genotype of the offspring from the first cross?

A: The genotype of the offspring from the first cross is BP or PB, which means they have one allele for red feathers (R) and one allele for blue feathers (B).

Q: What is the Punnett square for the second cross between two purple offspring?

A: The Punnett square for the second cross between two purple offspring is as follows:

	B
R	BR
P	BP

Q: What is the probability of each genotype in the second cross?

A: The probability of each genotype in the second cross is 50%, resulting in a 25% chance of purple offspring.

Q: What is the proportion of purple offspring in the second cross?

A: The proportion of purple offspring in the second cross is 25%.

Q: Why is the proportion of purple offspring in the second cross 25%?

A: The proportion of purple offspring in the second cross is 25% because the BP genotype has a 50% chance of being purple, and the BR genotype has a 50% chance of being red.

Q: What is the correct answer to the question about the proportion of purple offspring in the second cross?

A: The correct answer is A. 1 in 4.

Conclusion

In conclusion, incomplete dominance is a phenomenon in genetics where one allele does not completely dominate the other allele, resulting in a combination of the two alleles. The Punnett square can be used to calculate the probability of each genotype in a cross, and the proportion of offspring with a particular trait can be determined. In the case of the second cross between two purple offspring, the proportion of purple offspring is 25%.

Frequently Asked Questions

Q: What is the difference between incomplete dominance and complete dominance? A: Incomplete dominance is a phenomenon where one allele does not completely dominate the other allele, resulting in a combination of the two alleles. Complete dominance is a phenomenon where one allele completely dominates the other allele, resulting in the expression of the dominant allele.
Q: Can incomplete dominance occur in other traits besides feathers? A: Yes, incomplete dominance can occur in other traits besides feathers. For example, it can occur in the color of flowers or the shape of leaves.
Q: How can incomplete dominance be used in plant breeding? A: Incomplete dominance can be used in plant breeding to create new traits and improve crop yields. For example, it can be used to create plants with desirable traits such as disease resistance or drought tolerance.