Evaluating generations of fruit flies for inherited characteristics.

by zeynep_merve10hotmailcouk (student)

P1 Generation:

4 : 0

Large wing vestigial wing

The above ratio is phenotypic; as the predicted outcome of the F1 generation is 100% heterozygous, meaning they all have a dominant allele (A) and a recessive allele (a) for wing size, all the offspring’s show up to have large wings and none have vestigial wings. The female parent possesses large wings, it is assumed they are homozygous dominant (AA; A indicates large wing size); whereas, the male parent possesses vestigial wings, therefore they are homozygous recessive (aa; a indicates vestigial wing size) due to vestigial wings being recessive to large wings. Since the female parent has homozygous dominant alleles (AA) and the male parent has homozygous recessive alleles (aa), all offspring inherit one dominant allele (A) from the female parent and a recessive allele (a) from the male parent, resulting in heterozygous (Aa) alleles with large wings.

The class results for the F1 generation states 129:24 (Large wing: vestigial wing) and this result is relatively close to the predicted ratio of 4:0, the results obtained did not quite match our prediction. However, it could be said that the vestigial wings are small in number when compared to large wings, therefore they could be ignored.

F1 Generation:

3 : 1

Large wing vestigial wing

The above ratio is phenotypic; as the predicted outcome of the F2 generation is 75% Large wing and 25% vestigial wing, meaning 75% of them possess at least one dominant allele (A) (Offspring’s are AA and Aa with long wings) and 25% of them possess recessive alleles (a) for wing size (aa with vestigial wings). The female parent possesses large wings with heterozygous alleles (Aa), the male parent has the same heterozygous alleles (Aa) with large wings that are normal and dominant in fruit flies. The overall inheritance of the offsprings would be 25% homozygous dominant and 50% heterozygous, which would show up as large wings and a 25% will be homozygous recessive, which would show up as vestigial wings, as the F2 generation receives both a dominant allele (A) and a recessive allele (a) from the female parent and the male parent. Since the female parent is heterozygous (Aa) and the male parent is also heterozygous (Aa), one of the offspring will inherit the dominant allele (A) from the female parent and will also inherit a dominant allele (A) from the male parent, resulting in large wings. Two offspring will inherit one dominant allele (A) from the mother and a recessive allele (a) from the father fly, resulting again with large wings. Finally, one of the offspring will inherit both recessive alleles (aa) from the mother and father fly, resulting with vestigial wings. This will give the 3:1 ratio, as three of the offspring in total will show up as large wings and one will show up as vestigial wings.

The class results for the F2 generation states 115:48 (Large wing: vestigial wing) and this result is not as close to the predicted ratio of 3:1, the results obtained did not quite match our prediction because the number of large winged flies should have been at least about three times larger than the number of vestigial winged flies. However the large winged flies are around 2.4 times larger than the number of vestigial winged flies and it could be considered that it is only about two times the amount of vestigial winged flies.

Task 2 – Dihybrid ...

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Task 2 – Dihybrid Cross

P1 Generation:

1 : 1

Red eye White eye

Brown Body Brown Body

Female Male

The above ratio is phenotypic; as the predicted outcome of the F1 generation is: 50% of the fruit flies have red-eye + Brown body + Female characteristics; whereas 50% have white-eye + Brown body + Male characteristics. These predictions were obtained as male flies with red-eyes (XRY-) and black body (bb) were crossed with female flies with white-eyes (XrXr) and brown body (BB) in the P generation. The female parent possesses white eyes (XrXr) and brown body (BB), it is assumed that the brown body trait is homozygous dominant (BB; B indicates brown body colour) and will pass down only the Xr and B allele; whereas, the male parent possesses red-eyes (XRY-) and black body (bb), therefore its body colour trait is homozygous recessive (bb; b indicates black body colour) due to the black body colour being recessive to brown body colour, and will pass down the and b alleles. All offspring in the Punnett square have inherited a dominant allele (B) from the mother fly and a recessive allele (b) from the father fly, resulting all of them with brown bodies. At the same time, 8/16 (=1/2) of the offspring inherit one white eye allele (Xr) from the mother fly and a red eye allele (XR) from the father fly, resulting them to be female offspring (due to two copies of the X chromosome) with red eyes (due to red eyes being dominant to white eyes in fruit flies; only one copy of the red eye (XR) is sufficient to show up as red coloured eye). The other half- 8/16- inherit one white eye allele (Xr) from the mother fly and a Y chromosome from the father fly, resulting them to be male (due to one X chromosome and one Y chromosome) and white eyed (because the eye colour is sex linked, and is only carried by the X chromosome, also there is only one copy of the white eye allele). Overall, half the offspring are male, they have white eyes and brown bodies (XrY-Bb); half the offspring are female, they have red eyes and brown bodies (XRXr Bb).

The class results for the F1 generation states 3:11:26:6:35:8:2:0 (Red-eye, brown body, male: Red-eye, Black body, male: White-eye, Brown body, male: White-eye, black body, male: Red-eye, brown body, female: Red-eye, Black body, female: White-eye, Brown body, female: White-eye, black body, female). The results obtained do not accurately match our prediction which was a ratio of 1:1 (White-eye, Brown body, male: Red-eye, brown body, female). However, it could be said that the male individuals which are brown and white eyed along with the female individuals which are brown and red eyed, appear to be larger in number than the rest of the possibilities in the ratio. This shows that the results are slightly close to what we have predicted.

F1 Generation:

3: 1: 3: 1: 3: 1: 3: 1

(Red eye, Brown body, male: red eye, Black body, male: White eye, Brown body, male: white eye, Black Body, male: red eye, brown body, female: red eye, black body, female: White eye, brown body, female: white eye, black body, female)

The above ratio is phenotypic. These predictions were obtained as male flies with white-eyes (XrY-) and brown body (Bb) were crossed with female flies with red-eyes (XRXr) and brown body (Bb) in the F1 generation. The female parent possesses red-eyes (XRXr) and brown body (Bb) and will pass down the XR, Xr, b and B allele; whereas, the male parent possesses white-eyes (XrY-) and brown body (Bb) and will pass down the Xr, B and b alleles. The father fly only has one X chromosome that he passes down to the offspring’s that determine the eye colour, this is why the Y chromosome is not mentioned, however it does pass down this chromosome. Half of the offspring will be female and the other half will be male. This is due to the half the offspring inheriting an X chromosome from the mother and another X chromosome from the father (XX), resulting in homologous sex chromosomes and the gender being female. The other half inherit one X chromosome from the mother fly and a Y chromosome from the father fly, resulting as non-homologous sex chromosomes (XY) and the gender being male.

1/3 offspring inherit a recessive allele (b) from the mother and another recessive allele (b) from the father fly to determine the body colour as black. The 1/3 offspring will inherit one dominant allele (B) from the mother fly and one recessive allele (b) from the father fly, which will result in brown body. The other 1/3 will inherit one dominant allele (B) from the mother fly and another dominant allele (B) from the father fly, which will result in brown body.

Due to the fact that the eye colour determination is sex-linked and is passed down by the X chromosome, half the male offspring will inherit one white eye allele (Xr) from the mother fly and a Y chromosome from the father fly, resulting them to be white eyed (XrY-) (because the eye colour is sex linked, and is only carried by the X chromosome, only one copy is present which will show up as white eye colour); the other half of the male offspring will inherit one red eye allele (XR) from the mother fly and a Y chromosome from the father fly, resulting them to be red eyed (XRY-); half the female offspring will inherit one white eye allele (Xr) from the mother fly and another white eye allele (Xr ) from the father fly, resulting them to be white eyed (XrXr) (two copies of the white eye allele is present and will show up as white eye colour); the other half of the female offspring will inherit one red eye allele (XR) from the mother fly and another white eye allele (Xr) from the father fly, resulting them to be red eyed (XRXr) (as red eye alleles are dominant to white eye alleles, even one copy is sufficient to show up as red eye).

The class results for the F2 generation states 40:20:31:21:55:20:40:17 (Red eye, Brown body, male: red eye, Black body, male: White eye, Brown body, male: white eye, Black Body, male: red eye, brown body, female: red eye, black body, female: White eye, brown body, female: white eye, black body, female). The results obtained clearly do not accurately match our prediction which was a ratio of 3: 1: 3: 1: 3: 1: 3: 1 (Red eye, Brown body, male: red eye, Black body, male: White eye, Brown body, male: white eye, Black Body, male: red eye, brown body, female: red eye, black body, female: White eye, brown body, female: white eye, black body, female). However, it could be said that the red eye, brown body and male individuals share the same result as white eye, brown body and female individuals, which is 40, the ratio for these two is 3:3 (=1:1) from the findings in the Punnett square and the observed ratio is 40:40 (=1:1). Another slightly accurate result is the red eye, black body and male individuals share the same result as the red eye, black body and female individuals which is 20:20 (=1:1); and our predicted ratio was 1:1 between these two possibilities. This shows that some results do match our prediction, when compared with specific results; however, in general it is not quite accurate.