In Drosophila melanogaster, the genes for purple eyes (pr) and curved wings (c) are on the same chromosome. The recombination frequency between pr and c is roughly 20%. Both the purple eyed and curly winged phenotypes are recessive to the wild-type (+) phenotypes (red-eyed and straight winged, respectively).
Consider a cross between a female with genotype (+ c)/(pr +) and a male (pr c)/(pr c). Based on the information above, predict the percentage of offspring of each phenotype from this cross assuming a large number of offspring.
-Wild type (red eyes and straight wings)
-Purple eyes and Straight wings
-Red eyes and Curved wings
-Purple eyes and Curved wings
wILD tYPE - 10%
Purple/ Straight - 40%
Red/Curved - 40%
Purple/Curved - 10%
The recombinant genes stand for 20%, hence the 10-10 split.
To predict the percentage of each phenotype in the offspring, we need to consider the recombination frequency between the two genes (pr and c).
Given that the recombination frequency between pr and c is approximately 20%, we can assume that about 20% of the offspring will have a recombinant genotype, while the rest (80%) will have non-recombinant genotypes.
Let's break down the genotypes and phenotypes of the potential offspring:
1. Wild type (red eyes and straight wings): This phenotype corresponds to the non-recombinant genotype (+ c)/(pr +), where the wild type alleles are the dominant ones.
2. Purple eyes and Straight wings: This phenotype corresponds to the recombinant genotype (+ c)/(pr +), where one crossover event occurred between the pr and c genes during meiosis.
3. Red eyes and Curved wings: This phenotype corresponds to the non-recombinant genotype (pr c)/(pr +), where both genes are in the wild type configuration.
4. Purple eyes and Curved wings: This phenotype corresponds to the recombinant genotype (pr c)/(pr +), where there was a crossover event between the pr and c genes during meiosis.
Now, let's calculate the percentages of each phenotype:
- Wild type: Since the reciprocal crossover frequency is 20% and the non-recombinant genotypes comprise 80% of the offspring, the percentage of wild-type offspring would be 80%.
- Purple eyes and Straight wings: Again, the recombinant genotypes represent 20% of the offspring, so the percentage of these offspring would also be approximately 20%.
- Red eyes and Curved wings: Since this is a non-recombinant genotype, it would also account for 80% of the offspring.
- Purple eyes and Curved wings: This is a recombinant genotype, so it would represent around 20% of the offspring.
Therefore, the predicted percentage of each phenotype would be as follows:
- Wild type (red eyes and straight wings): 80%
- Purple eyes and Straight wings: 20%
- Red eyes and Curved wings: 80%
- Purple eyes and Curved wings: 20%
To predict the percentage of offspring of each phenotype, we need to understand how the genes for purple eyes (pr) and curved wings (c) are inherited in Drosophila melanogaster, as well as the recombination frequency between these two genes.
In this case, the female has the genotype (+ c)/(pr +), which means she has a wild-type allele for eyes (red eyes) and a mutant allele for wings (curved wings). The male has the genotype (pr c)/(pr c), meaning he has mutant alleles for both eyes (purple eyes) and wings (curved wings).
First, let's determine the possible gametes that each parent can produce:
- Female: She can produce gametes with (+ c) and (pr +)
- Male: He can only produce gametes with (pr c)
Since the male can only produce one type of gamete, all his gametes will carry both the mutant alleles (pr c).
To predict the offspring phenotypes, we need to consider the combinations of these gametes.
The possible combinations are:
- (+ c) x (pr c): This will give rise to offspring with the following genotypes: (+ c)/(pr c) and (+ c)/(pr +). These individuals will have a wild-type phenotype for eyes (red eyes) and a mutant phenotype for wings (curved wings).
- (pr +) x (pr c): This will give rise to offspring with the genotype (pr +)/(pr c), where they will have a wild-type phenotype for eyes (red eyes) and wings (curved wings).
Therefore, the predicted percentages of offspring phenotypes are as follows:
- Wild type (red eyes and straight wings): Approximately 50% [(+ c)/(pr c) + (+ c)/(pr +)]
- Purple eyes and Straight wings: Approximately 25% [(pr +)/(pr c)]
- Red eyes and Curved wings: Approximately 25% [(+ c)/(pr c)]
- Purple eyes and Curved wings: 0% (Since the female does not carry the pr allele, it cannot be inherited by the offspring)
Please note that these percentages are based on the assumption of a large number of offspring, meaning that the predicted ratios may not be observed exactly in a small sample size.