Let’s suppose that you have made a karyotype of a female fruit fly with red eyes and found that it has three X chromosomes instead of the normal two. Although you do not know its parents, you do know that this fly came from a mixed culture of flies in which some had red eyes, some had white eyes, and some had eosin eyes. Eosin is an allele of the same gene that has white and red alleles. Eosin is a pale orange color. The red allele is dominant and the white allele is recessive. The expression of the eosin allele, however, depends on the number of copies of the allele. When females have two copies of this allele, they have eosin eyes. When females are heterozygous for the eosin allele and the white allele, they have light-eosin eyes. When females are heterozygous for the red allele and the eosin allele, they have red eyes. Males that have a single copy of the eosin allele have eosin eyes. You cross the XXX red-eyed female with a white-eyed male and count the numbers of offspring. You may assume that this unusual female makes half of its gametes with one X chromosome and half of its gametes with two X chromosomes. The following results for the offspring were obtained:
Females* | Males | |
Red eyes | 50 | 11 |
White eyes | 0 | 0 |
Eosin | 20 | 20 |
Light-eosin | 21 | 0 |
*A female offspring can be XXX, XX, or XXY
Explain the 3:1 ratio between female and male offspring. What is the genotype of the original mother, which had red eyes and three X chromosomes? Construct a Punnett square that is consistent with these data.
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Genetics: Analysis and Principles
- Imagine that you are a new breeder for caique parrots. You can sell normal green feather birds for $500 a bird. The mutation for blue feathers is rare and birds with this color can sell for $3000 a bird. Your goal is to produce as many blue feather offspring as you can, but you don't have the budget to buy blue feather birds as parents. Question: What genotype should you purchase for both parent blrds to get the best chance of getting blue feather offspring? Create and use your Punnett square results as evidence to support your answer. You will need to make multiple Punnett Squares to see which parent genotypes makes the most blue feathered offspring. Keep in mind that Green fealhers (G) is dominant over blue feathers (g), so birds with blue feathers have the genotype gg. Some Punnett squares are provided for you to determine the possible crosses, but remember yoU cannot afford a blue feathered bird, so neither of your parent birds can have the genotype gg. Complete a Punnett Square…arrow_forwardIn Drosophila, red eyes is the wild-type phenotype. There are several different genes that affect eye colour. One allele causes purple eyes, and a different allele causes sepia eyes. When flies with purple eyes were crossed with flies with sepia eyes, all of the F1 offspring had red eyes. The F1 offspring were allowed to mate with each other and the following data were obtained: 146 purple eyes201 sepia eyes444 red eyes Formulate a hypothesis that you think is consistent with the observed data. Test the goodness of fit between the data and your hypothesis.arrow_forwardA new gene is being investigated in fruit flies. The recessive allele of this gene (b) causes the wings to develop a blue color, while the dominant allele (b+) permits wild-type colorless wings to develop. Preliminary studies indicate that this new gene is located on the X-chromosome. You decided to perform a two-point testcross to determine its positionrelative to the well-established garnet eyes gene (g). You cross a female heterozygous for both genes with a testcross male fly and obtain the male offspring results shown in table 1, below. Is the original female a coupling or repulsion heterozygote? What is the map distance between genes b and g?. Based on these results, gene b must be located between what two genes on the map? You perform another two-point testcross between gene b and gene v and obtained the results in table 2, below. Now, you can localize gene b to be specifically between which two genes?arrow_forward
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