Assignment #1: Epistasis
- What did you observe in the F1 generation?
The F1 generation was comprised of wild types in terms of wing size and wing vein.
Was this what you expected? Why or why not?
Yes. The wing mutation and the vestigial wing size genes are recessive and hence would not be expressed.
Once you have produced an F1 generation, mate F1 flies to generate an F2 generation.
Study the results of your F2 generation and then answer the following questions.
Which mutation is epistatic?
The vestigial wing gene is the epistatic one.
Is the vestigial mutation dominant or recessive?
The vestigial mutation is recessive.
Determine the phenotypic ratio that appeared in the dihybrid F2 generation, and use chi-square analysis to accept or reject this ratio.
The resulting phenotypic ratio was wild: VG: RI = 3: 1: 1 and the results for the chi-square where that the hypothesis should be rejected.
- Perform another experiment by mating a female fly with the apterous wing size mutation with a male fly with the radius incomplete vein structure mutation. Follow this cross to the F2 generation.
Which mutation is epistatic?
The apterous wing size mutation is the epistatic one.
Is the apterous wing mutation dominant or recessive?
The apterous wing mutation is the recessive allele.
Assignment #2:
- Draw a map that shows the map distance (in map units or centimorgans) between the locus for the shaven bristle allele and the locus for the eyeless allele.
- What is the phenotype of these flies?
The phenotypes of the flies were wild, purple eyes, vestigial wings, purple with vestigial wings, black body, purple eyes with black body, vestigial wings with black body and purple eyes, vestigial wings and black body.
What does this tell you about the position of the purple eye allele compared with the black body and vestigial wing alleles?
This shows that the purple eye allele is located between the black body and the vestigial wing alleles.
Sketch a genetic map indicating the relative loci for each of these three alleles, and indicate the approximate map distance between each locus.
Assignment #3: Group Assignment
- For each dihybrid cross, answer the following questions. Perform additional experiments if necessary to answer these questions.
- Which of these traits are dominant and which traits are recessive?
The first cross was between a male with white eyes and a female fly with singed bristles. The singled bristle traits were dominant while the white eyes were recessive.
The second cross was between a male with star eyes and a female with dichaete wings. Both the traits were dominant.
The third cross was between a male with yellow body and a female with miniature wings. The yellow body trait was recessive while the miniature wings were dominant.
- Are any of these mutations lethal in a homozygous fly? Which ones?
- Are any of the alleles that you followed sex-linked? How do you know this?
Yes. The miniature wings were dominant and were only expressed in the male flies. This showed that the allele is located in the y chromosome.
- Which alleles appear to be inherited on autosomes?
- If any of the genes was linked, what is the map distance between these genes?
The alleles of the white eyes and singed bristles are linked, and their map is as follows.
- For at least one of your crosses, attempt to perform the cross on paper using a Punnett square to confirm the results obtained by FlyLab.
- Ask another pair of students to carry out one of the crosses that you designed. Did they get the same results that you did in the F1 and F2 generations? Did they develop the same hypotheses to explain the results of this mating as you did? Explain your answer.
Those who performed the designed crosses got the same results in terms of the phenotypic ratio with some variations in the numbers in the different phenotypes as well as in the total. They did set hypothesis where some were accepted while others rejected.
- Once you have completed this exercise, discuss your results with your instructor to determine if your observations and predictions were accurate.
