A novel mutation in eye color of Drosophila appears. Instead of wild type red eyes, the flies have eyes that are a dark shade of orange, hence they are called pumpkin. Nine female offspring of one cross have the mutation.No male offspring have the mutation. The probability of this happening by chance is 2-9 or 0.00195.
- Based on the above, the chromosome most likely to carry this mutation is the X chromosome. How did they reach that conclusion?
- What phenotype(s) would you predict for the F1 progeny of this cross?
It is stated that the males are normal and the females are affected. So, this links the mutation to the X-chromosome
If this is, indeed, on the X chromosome, the next question is where on the X chromosome?
Fortunately we have additional mutants which have been mapped to the same chromosome we believe pumpkin is on. One mutant phenotype is expressed as miniature wings (m), the other is expressed as forked sensory bristles (f).
Experiment:undefined
The parental generation consisted of female triple recessive mutants homozygous for pumpkin eyes (p), miniature wings (m), and forked bristles (f). These were crossed with males that were true breeding wild type for all three traits (+++)
What genotype(s) would you predict for the F1 progeny?
The F1 siblings were crossed with each other.The following F2 results were obtained split evenly between males and females:
|
Phenotype |
Count |
|
+++ |
3230 |
|
fmp |
2230 |
|
++p |
1237 |
|
fm+ |
1200 |
|
f++ |
822 |
|
+mp |
877 |
|
+m+ |
166 |
|
f+p |
238 |
|
Total |
10,000 |
undefinedTable 1
undefined3)If the three genes were sorting independently on the X chromosome
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undefinedHow many phenotypes would be expected in F1?
undefinedWhat would be the expected phenotypes in F1?
undefinedHow many genotypes would there be in F2?
undefinedWhat would be the expected genotypes in F2?
undefinedHow many of each phenotype would you expect in a total of 10,000 observations? (show work on this worksheet). This should be shown using the fork line method.
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- Use the Chi-square analysis available online
- Based on the results from Table #1, and your conclusion from #4, Map the genes below:
- What conclusions can you reach about the chromosomal location of the three genes?
- Fork line method and epistasis.
undefinedhere: https://goodcalculators.com/chi-square-calculator/ )
undefinedand the lookup table below:
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undefinedCompare the expected results (from #3) for three independently sorting genes with the 10,000 observed results (Table 1). What can you conclude about the linkage between these three genes? Explain your answer.(show work below)
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undefinedNow you know that Mendel did NOT develop his theory based on experiments with pea plants by looking at the color of their flowers. However, his theory still works once you know about epistasis.
undefinedUse the fork line method to explain predict the results one would expect to obtain using the double recessive epistatic phenotype of flower color.(https://www.yourarticlelibrary.com/biology/6-most-important-kinds-of-epistasis-biology/6436)
