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Drosophila Genetics Lab

Darsh Patel and Cian Desai for AP Biology Block 2
by

Darsh Patel

on 28 February 2016

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Transcript of Drosophila Genetics Lab

Conclusion
Purpose
Hypothesis
Prediction formulated after performing the first cross between a true-breeding female with scalloped wings and a wild-type male
We predicted that scalloped wings are a recessive, sex-linked trait.
We arrived at this prediction due to the fact that the F1 generation resulted in 100% of the female offspring being wild-type and 100% of the male offspring having scalloped wings.
This means that the true breeding female would have given its female offspring an X chromosome which contains the recessive allele only to have it masked by the dominant allele (on the X chromosome given by the male). The male offspring would be given the recessive allele from the female parent which would be expressed due to the presence of only one X chromosome.
If this is true, then the F2 generation will result in:
50% of the females being wild-type
50% of the females having scalloped wings
50% of the males being wild-type
50% of the males having scalloped wings.
Results of First Crosses
The cross of the P generation produced all wild-type females (586) and all scalloped-wing males (597).
When the F1 generation was crossed, 322 scalloped-wing females, 318 scalloped wing males, 282 wild-type females, and 295 wild-type males were produced.
Our theoretical yield for the F2 generation, assuming our hypothesis was correct was 304 scalloped-wing females, 304 scalloped-wing males, 304 wild-type males, and 305 wild-type females.
To make sure our actual data coincided with our theoretical yield, we ran a Chi-Square Test to determine just how accurate we were
Results of Second Crosses
In the world of science, you can never have too much proof.
We began again, only this time we crossed a MALE drosophila with scalloped-wings and a wild-type FEMALE as our P generation.
If our hypothesis is correct, this should have yielded 100% of males as wild-type and 100% of females as wild-type (all of the offspring would be wild-type).
Our actual yield for the F1 generation was 605 wild-type females and 585 wild-type males, so our predicted yield held true.
Results of Second Crosses (cont.)
After the F1 generation was produced, we decided to cross them to receive an F2 generation.
Theoretically, this cross would produce 591 wild-type females, 295 wild-type males, and 296 wild-type males.
Our actual yield for the F2 generation was 591 wild-type females, 321 wild-type males, and 287 scalloped-wing males.
Again, to make sure our actual data coincided with our theoretical yield, we conducted a Chi-Square Test.
Data
First Set of Crosses (P Gen: F SW x M WT)
Drosophila Genetics Lab
Darsh Patel and Cian Desai
This lab was conducted to study the traits of Drosophila melanogaster.
Conducted in hopes of understanding the behavior of certain alleles within the fruit fly species.
The phenotypes of the offspring are dependent on the genetic makeup (genotypes) of the two parents.
Wild-Type Drosophila Fly
Part 4
Part 4
Part 4
Hold Up, What Are We Doing In This Cross?
The resulting F2 Generation shows the 8 different phenotypes of the flies, some having recombinant DNA.
DATA
Great question! This cross examined linked genes, or genes that are located on the same chromosome.
To test this, two genes were chosen: Body color (black body) and eye color (purple eyes).

Parental Generation
: Black Body
(
BL
)
,
Purple-Eyed

(
PR
)

Female

&

Wild-Type

Male
F1 Generation:

Male
Offspring:

Wild-Type

(581)
Female

Offspring:

Wild-Type
(593)
Second Cross:
Female

Wild-Type
(from
F1 Generation
) &
Black Body
,
Purple-Eyed

Male
F2 Generation:
Male
Offspring:
291
PR
,
BL
(Mutated)
274
Wild-Type
13
PR
,
Wild-Type
Body
18
BL
,
Wild-Type
Eyes
Female
Offspring:
278
PR
,
BL
(Mutated)
286
Wild-Type
20
PR
,
Wild-Type
Body
17
BL
,
Wild-Type
Eyes
Cross between P Generation
Possible outcomes: 4
Degrees of freedom: 3
Chi-Square Statistic: 3.7114 (which is less than the alotted 7.82 with 3 degrees of freedom at p=0.05)
This shows that our data is reliably close enough to our theoretical outcomes.
Chi-Square Stats:
Cross between the F1 generation (this is where our theoretical yield came from)
Parental Generation Cross
There are
4 recombinant DNA phenotypes
, two for
male
and two for
female
. These can be identified because there are more parental combinations and a smaller number of recombinant phenotypes.
Recombinant DNA Phenotypes
P Generation Cross
Drosophila w/ scalloped wings
Linkage Map
Map Units (approximately how far apart are these genes located on the chromosome?):
20+13+17+18
_______________________
291+278+13+20+17+18+286+274
=
68
___
1197
=
*100
5.68% OR 5.68 map units
Chi-Square Stats
Side Note
: Recombinant divided by total gives percentage, which is equal to map units because 1%=1 map unit
Possible outcomes: 3
Degrees of Freedom: 2
Chi-Square Statistic: 3.0542 (which is less than the alotted 5.99 with 2 degrees of freedom at p=0.05)
This shows that our data is reliably close enough to our theoretical outcomes.
Cross between the F1 generation, this is where our theoretical yield came from
31.47 map units between Wing Shape and Eye Color
21.60 map units
5.68 map units
Second Set of Crosses (P Gen: F WT x M SW)
F1 Generation
F2 Generation
Chi-Square Test and Table for F2 Gen
Curved Wings
Wild-Type Wings
Wild-Type Body Color
Wild-Type Eye Color
F1 Generation
Black Body
Purple Eyes
F2 Generation
Chi-Square Test for F2 Gen
Part 4
Part 4
Sources (well really source) of Error
Rounding numbers while conducting the chi-square tests may have resulted in deviated chi-square statistics.
This lab
seemingly
proved that the genes for scalloped wings is recessive and sex-linked.
First Cross-F1 Generation:
If the genes were really recessive and sex-linked, the F1 Generation would be 50% female wild-type and 50% male scalloped wings.
This is because the recessive allele on the X chromosome (from the female parent) translates to the male offspring while the dominant allele on the X chromosome (from the male parent) translates to the female offspring, so the males would have scalloped wings and the females would have wild-type wings.
This was the case, and was the first degree of proof.
First Cross-F2 Generation:
We predicted the F2 Generation to be approximately 25% female wild-type, 25% female scalloped wings, 25% male wild-type, and 25% make scalloped wings.
The chi-squared analysis proved that our actual results reflected our predictions.
A second cross was implemented to further prove the fact that the gene for scalloped wings is recessive and sex-linked.
Second Cross-F1 Generation:
If the genes were really recessive and sex-linked, the F1 Generation would be 50% female wild-type and 50% male wild-type.
This is because the recessive allele on the X chromosome (from the male parent) translates to the female, but is masked by the dominant allele from the female parent, yeilding wild-type female offspring, and the dominant allele on the X chromosome (from the female parent) translates to the male, yielding wild-type male offspring.
Second Cross- F2 Generation:
We predicted that the F2 Generation to be 50% female wild-type, 25% male wild-type, and 25% male scalloped wings.
The chi-squared analysis proved that our actual results reflected our predictions.
Although we have a relative amount of backup to argue a case that the wing shape gene in Drosophila is sex-linked, no definitive statements can be made due to our small sample size.
This being said, for further experimentation we can conduct more trials of the same crosses, or cross F1 offspring with either true-bred wild type Drosophila or scalloped-wing Drosophila.
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