IB Bio HL Virtual Fly Lab OMG

1. Hyohyun Lee
IB Biology HL: Period 5
April 7th, 2010
1
Virtual Fly Lab
Introduction
Gregor Johann Mendel’s experiments with garden peas dramatically influenced the field of
biology. Mendel’s results became the foundation for the discipline known as genetics, which is the
study of variation and inheritance. Mendel’s experiments were done by using varieties of pea plant.
He crossed those varieties of pea together by transferring the male pollen from one variety to the
female parts in flowers of another variety artificially. He considered seven different characters
including flower color, flower position, seed color, seed shape, pod color, pod shape, and stem length.
Variations of a given character are known as traits. Then, he collected the seeds and grew them to
find out what their characteristics looked like. Later his results were surprising; characteristics from
the original parents had disappeared or reappeared in their offspring. During his experiments, he
discovered that there were particles of inheritance factors, which are now called genes. Specifically,
genes are heritable factors that control a specific characteristic. Mendel also thought that were
alternative forms of a gene which were responsible for variations in inherited characters. Those
forms of a gene are now called alleles. After he got surprising results, he observed that the ratio of
pea plants was always close to 3:1, dominant alleles : recessive alleles. For instance, in the pea plants
that Mendel used have two alleles for stem length, a tall stem and a dwarf stem. With true-breeding
homozygous parents called the P generation, he first crossed a tall plant with a dwarf plant. The first
offspring, called the F1 generation, were all tall. This is because a tall stem is a dominant character in
pea plant and a dwarf stem is a recessive character. In F2 generation from the self-pollination of F1
plants, the phenotype ratio of tall plants to dwarf plants was approximately 3:1. Here, Mendel
discovered that this ratio was made from a cross between heterozygotes. He also used dihybrid
crosses in order to explain his law of independent assortment, which is that alleles for different
characters segregate into each gamete independently. In a dihybrid cross, the phenotype ratio of
heterozygous F1 cross is approximately 9:3:3:1 in F2 generation. Furthermore, Punnett square is
useful to predict the genotypes and phenotypes from a genetic cross.
Chi-square analysis is a statistical test that makes a comparison between the data collected in
an experiment and expected data. In genetics, the Chi-square analysis used to evaluate data from
experimental crosses to determine if the assumed genetic explanation is supported by the data.
The person who originally proposed the use of the fruit fly was Thomas Hunt Morgan while
he worked at Columbia University in the early 1900’s. For his genetics work with fruit fly, he
received the Nobel Prize in Medicine in 1933. In this virtual Fly Lab, fruit flies, also called

2. Hyohyun Lee
IB Biology HL: Period 5
April 7th, 2010
2
Drosophila melanogaster, will be used. In addition, with Punnett square, Chi-square analysis, and
other basic knowledge, it will be easy to simulate basic principles of genetic inheritance based on
Mendel’s genetics by performing crosses between fruit flies. The Chi-square analysis will be used so
that I can accept or reject my hypothesis for the expected phenotype ratio of offspring for each cross.
The tasks of this lab are to investigate traits of fruit flies and to show proof that I have found traits
which are inherited in the following five manners: a dominant allele, a recessive allele, a recessive
sex-linked allele, a dominant lethal allele, and dihybrid cross.
In this lab, there will be also used some genetic abbreviations. The normal “wild type”
version will be represented as “+”. A table of the genetic abbreviations used in this lab appears below.
Table 1) The Genetic Abbreviations
Abbreviation Phenotype Abbreviation Phenotype Abbreviation Phenotype
AP Apterous Wings EY Eyeless Eyes SE Sepia Eyes
AR Aristapedia
Antennae
DP Dumpy Wings SN Singed
Bristles
B Bar Eyes F Forked
Bristles
SS Spineless
Bristles
BL Black Body L Lobe Eyes ST Star Eyes
BW Brown Eyes M Miniature
Wings
SV Shaven
Bristles
C Curved Wings PR Purple Eyes T Tan Body
CV Crossveinless
Wings
RI Radius
Incompletus
Wings
VG Vestigial
Wings
CY Curly Wings S Sable Body W White Eyes
D Dichaete
Wings
SB Stubble
Bristles
Y Yellow Body
E Ebony Body SD Scalloped Wings

3. Hyohyun Lee
IB Biology HL: Period 5
April 7th, 2010
3
A dominant allele (Eye shape Bar Female x Wild type Male)
A dominant allele is an allele that has the same effect on the phenotype whether it is present
in the homozygous or the heterozygous state. To test for a dominant allele, the character of lobe eyes
is used because this character is assumed as a dominant allele. In this cross, one of the parents must
have identical lobe eyes allele and another must be a wild fruit fly.
F1
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Results of Cross #27
Ignoring Sex
Parents
(Female: B) x (Male: +)
Offspring
Phenotype Number Proportion Ratio
B 1016 1.0000 1.000
Total 1016
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Chi Square Hypothesis Using Cross #27
Ignoring Sex
Phenotype Observed Hypothesis Expected Chi-Square Term
B 1016 1.0000 1016.0000 0.0000
Total 1016 1.0000 1016.0000 0.0000
Chi-Squared Test Statistic = 0.0000
Degrees of Freedom = 0
Level of Significance = 1.0000
Recommendation: Do not reject your hypothesis
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Explanation:
From this data, it is shown that when a fly with homozygous bar eyes mates with a fly with
wild type eyes, the resulting offspring only has bar type eyes. This evidence can suggest that bar eye
shape is the dominant allele over wild type because in order for the offspring to have only have bar
eye shape from parents that have different homozygous allele, the bar eye shape must be the
dominant allele. This is shown in the Punnett square below:
B = Bar Eyes + = Wild Type
Table 2) Punnett Square for a Cross between Bar Eyes Female and Wild Eyes Male
B B
+ B+ B+
+ B+ B+
Genotype of the offspring = B+
Phenotype of the offspring = All Bar eyes (supported by the result of cross #27)

4. Hyohyun Lee
IB Biology HL: Period 5
April 7th, 2010
4
F2
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Results of Cross #28
Ignoring Sex
Parents
(Female: B) x (Male: B)
Offspring
Phenotype Number Proportion Ratio
+ 251 0.2505 1.000
B 751 0.7495 2.992
Total 1002
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Chi Square Hypothesis Using Cross #28
Ignoring Sex
Phenotype Observed Hypothesis Expected Chi-Square Term
+ 251 1.0000 250.5000 0.0010
B 751 3.0000 751.5000 0.0003
Total 1002 4.0000 1002.0000 0.0013
Chi-Squared Test Statistic = 0.0013
Degrees of Freedom = 1
Level of Significance = 0.9709
Recommendation: Do not reject your hypothesis
----------------------------------------------------------------------------------------------------------------
Explanation:
From Cross #28, it further supports that bar eye is the dominant allele for eye shape. As
suggested from the previous Punnett Square, the F1 generation only has a bar eye shape phenotype
with genotype of B+. When these heterozygotes cross together, they are expected to produce F2
generation with a phenotype ratio, 3:1 for bar eye shape to wild eye shape, as shown in the Chi-
Square #28 above. According the Chi-squared test, the result is not statistically significant because
the result is nearly accurate compared to the expected data. This can only suggest that bar eye shape
is the dominant allele and this is shown in the Punnett square below:
B = Bar Eyes + = Wild Type
Table 3) Punnett Square for a Cross between Heterozygous Bar Eye Parents
B +
B BB B+
+ B+ ++
Genotype ratio of the offspring – BB : B+ : ++ = 1:2:1
Phenotype ratio of the offspring – Bar Eyes : Wild Eyes = 3:1

5. Hyohyun Lee
IB Biology HL: Period 5
April 7th, 2010
5
A recessive allele (Wing shape Dumpy Female x Wild type Male)
A recessive allele is an allele that only has an effect on the phenotype when it is present in
the homozygous state. In this case, dumpy wing shape is assumed as a recessive allele. Therefore, if
dumpy wing shape female and wild type male cross together, they will breed offspring that has all
phenotype with wild wing shape.
F1
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Results of Cross #3
Ignoring Sex
Parents
(Female: DP) x (Male: +)
Offspring
Phenotype Number Proportion Ratio
+ 1004 1.0000 1.000
Total 1004
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Chi Square Hypothesis Using Cross #3
Ignoring Sex
Phenotype Observed Hypothesis Expected Chi-Square Term
+ 1004 1.0000 1004.0000 0.0000
Total 1004 1.0000 1004.0000 0.0000
Chi-Squared Test Statistic = 0.0000
Degrees of Freedom = 0
Level of Significance = 1.0000
Recommendation: Do not reject your hypothesis
--------------------------------------------------------------------------
Explanation:
From this data, it is shown that when a fly with homozygous dumpy wings mates with a fly
with wild type wings, the resulting offspring only has wild type wings. This evidence can suggest
that dumpy wing shape is the recessive allele over wild type wing because in order for the offspring
to have only wild wing shape from parents that have different homozygous allele, the dumpy wing
shape must be the recessive allele. This is shown in the Punnett square below:
DP = Dumpy Wings + = Wild Type
Table 4) Punnett Square for a Cross between Dumpy Wings Female and Wild Wings Male
DP DP
+ DP+ DP+
+ DP+ DP+
Genotype of the offspring = DP+
Phenotype of the offspring = All Wild Wings (supported by the result of cross #3)

6. Hyohyun Lee
IB Biology HL: Period 5
April 7th, 2010
6
F2
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Results of Cross #4
Ignoring Sex
Parents
(Female: +) x (Male: +)
Offspring
Phenotype Number Proportion Ratio
+ 741 0.7647 3.250
DP 228 0.2353 1.000
Total 969
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Chi Square Hypothesis Using Cross #4
Ignoring Sex
Phenotype Observed Hypothesis Expected Chi-Square Term
+ 741 3.0000 726.7500 0.2794
DP 228 1.0000 242.2500 0.8382
Total 969 4.0000 969.0000 1.1176
Chi-Squared Test Statistic = 1.1176
Degrees of Freedom = 1
Level of Significance = 0.2904
Recommendations: Do not reject your hypothesis
--------------------------------------------------------------------------
Explanation:
From Cross #4, it further supports that dumpy wing is the recessive allele for wing shape. As
suggested from the previous Punnett Square, the F1 generation only has wild wing shape phenotype
with genotype of DP+. When these heterozygotes cross together, they are expected to produce F2
generation with a phenotype ratio, 3:1 for wild wing shape to dumpy wing shape, as shown in the
Chi-Square #4 above. According the Chi-squared test, the result is statistically significant because
the result is not that accurate compared to the expected data and the hypothesized rate. This can only
suggest that dumpy wing shape is the recessive allele over wild wing shape and this is shown in the
Punnett square below:
DP = Dumpy Wings + = Wild Type
Table 5) Punnett Square for a Cross between Heterozygous Wild Wing Parents
DP +
DP DPDP DP+
+ DP+ ++
Genotype ratio of the offspring – DPDP : DP+ : ++ = 1:2:1
Phenotype ratio of the offspring – Wild Wings : Dumpy Wings = 3:1

7. Hyohyun Lee
IB Biology HL: Period 5
April 7th, 2010
7
A recessive sex-linkedallele (Wild type Female x Body color Sable Male)
A recessive sex-linked allele is an allele which appears in sex chromosome, X chromosome.
Crossing a wild type female with a sable color male is the first step to find a recessive sex-liked
allele.
F1
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Results of Cross #5
Parents
(Female: +) x (Male: S)
Offspring
Phenotype Number Proportion Ratio
Female: + 488 0.4905 1.000
Male: + 507 0.5095 1.039
Total 995
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Chi Square Hypothesis Using Cross #5
Phenotype Observed Hypothesis Expected Chi-Square Term
Female: + 488 1.0000 497.5000 0.1814
Male: + 507 1.0000 497.5000 0.1814
Total 995 2.0000 995.0000 0.3628
Chi-Squared Test Statistic = 0.3628
Degrees of Freedom = 1
Level of Significance = 0.5469
Recommendation: Do not reject your hypothesis
--------------------------------------------------------------------------
Explanation:
From this data, it is shown that when a fly with normal color crosses with a fly having
homozygous sable color, the resulting offspring only has wild body color. This evidence can suggest
that sable body color is included in the recessive sex-linked allele over the wild body color because
in order for the offspring to have only wild body color from parents that have different homozygous
allele, the sable body color must be the recessive sex-linked allele. This is shown in the Punnett
square below:
S = Sable Body + = Wild Body
Table 6) Punnett Square for a Cross between Wild Body Color Female and Sable Color Male
XS Y
X+ XSX+ X+Y
X+ XSX+ X+Y
Genotype of the offspring = XSX+, X+Y
Phenotype of the offspring = All Wild Body Color (supported by the result of cross #5)

8. Hyohyun Lee
IB Biology HL: Period 5
April 7th, 2010
8
F2
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Results of Cross #6
Parents
(Female: +) x (Male: +)
Offspring
Phenotype Number Proportion Ratio
Female: + 509 0.4947 2.004
Male: + 254 0.2468 1.000
Male: S 266 0.2585 1.047
Total 1029
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Chi Square Hypothesis Using Cross #6
Phenotype Observed Hypothesis Expected Chi-Square Term
Female: + 509 2.0000 514.5000 0.0588
Male: + 254 1.0000 257.2500 0.0411
Male: S 266 1.0000 257.2500 0.2976
Total 1029 4.0000 1029.0000 0.3975
Chi-Squared Test Statistic = 0.3975
Degrees of Freedom = 2
Level of Significance = 0.8198
Recommendation: Do not reject your hypothesis
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Chi Square Hypothesis Using Cross #6
Ignoring Sex
Phenotype Observed Hypothesis Expected Chi-Square Term
+ 763 3.0000 771.7500 0.0992
S 266 1.0000 257.2500 0.2976
Total 1029 4.0000 1029.0000 0.3968
Chi-Squared Test Statistic = 0.3968
Degrees of Freedom = 1
Level of Significance = 0.5287
Recommendation: Do not reject your hypothesis
--------------------------------------------------------------------------
Explanation:
From Cross #6, it further supports that sable body color is the recessive sex-linked allele for
body color. As suggested from the previous Punnett Square, the F1 generation only has wild body
color phenotype with genotype of S+. When these heterozygotes cross together, they are expected to
produce F2 generation with a phenotype ratio, 3:1 for wild body color to sable body color, as shown
in the Chi-Square #6 above. According the Chi-squared test, the result is not statistically significant
because the result is nearly accurate compared to the expected data and the hypothesized rate. This
can suggest that sable body color is the recessive sex-linked allele over wild body color and this is
shown in the Punnett square in next page:

9. Hyohyun Lee
IB Biology HL: Period 5
April 7th, 2010
9
S = Sable Body + = Wild Body
Table 7) Punnett Square for a Cross between Heterozygous Wild Body Color Parents
X+ Y
XS XSX+ XSY
X+ X+X+ X+Y
Female genotype ratio of the offspring – XSX+ : X+X+ = 1:1
Female phenotype ratio of the offspring – All Wild Body Color
Male genotype ratio of the offspring – XSY : X+Y = 1:1
Male phenotype ratio of the offspring – Sable Body Color : Wild Body Color = 1:1
A dominant lethal allele (Wing angle Dichaete Female x Wing angle Dichaete Male)
A lethal allele is an allele that can cause death if organisms have homozygous dominant
allele. For fruit flies, dichaete wing angle is one of the lethal alleles. The reason is that when two
fruit flies with the same trait, dichaete wing angle, are mated, the ratio is 2:1, dichaete wing angle :
wild wing angle. Here, the one that survives and that will be used for mating has to be carrier
because homozygous dichaete wing angle fly cannot live anymore.
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Results of Cross #13
Ignoring Sex
Parents
(Female: D) x (Male: D)
Offspring
Phenotype Number Proportion Ratio
+ 350 0.3418 1.000
D 674 0.6582 1.926
Total 1024
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Chi Square Hypothesis Using Cross #13
Ignoring Sex
Phenotype Observed Hypothesis Expected Chi-Square Term
+ 350 1.0000 341.3333 0.2201
D 674 2.0000 682.6667 0.1100
Total 1024 3.0000 1024.0000 0.3301
Chi-Squared Test Statistic = 0.3301
Degrees of Freedom = 1
Level of Significance = 0.5656
Recommendation: Do not reject your hypothesis
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10. Hyohyun Lee
IB Biology HL: Period 5
April 7th, 2010
10
Explanation:
From this data, it is shown that when two flies with the same trait, dichaete wing angle, the
resulting offspring only has wild wing angle and dichaete wing angle. However, we can know that by
drawing a Punnett square, the homozygous dichaete wing angle flies are dead because the trait is a
lethal allele. This evidence can suggest that dichaete wing angle is included in the lethal allele
because in order for the offspring to have the ratio of 2:1, dichaete wing angle : wild wing angle, the
dichaete wing angle must be the lethal allele. This is shown in the Punnett square below:
D = Dichaete Wings + = Wild Wings
Table 8) Punnett Square for a Cross between two dichaete wing angle parents
D +
D DD (died) D+
+ D+ ++
Genotype of the offspring = DD (died), D+, ++
Phenotype of the offspring = Dichaete Wing, Wild Wing (supported by the result of cross #13)
Genotype ratio of the offspring – DD (died) : D+ : ++ = 1:2:1
Phenotype ratio of the offspring – Dichaete Wing : Wild Wing = 2:1 (because one dichaete wing fly
is dead)

11. Hyohyun Lee
IB Biology HL: Period 5
April 7th, 2010
11
Dihybrid Cross (Wild type Female x Wing size Apterous & Eye color Sepia Male)
The 9:3:3:1 ratio is often found when parents that are heterozygous for two genes are
crossed together. The dihybrid cross follows Mendel’s Law of Independent Assortment because the
genes are unlinked.
F1
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Results of Cross #7
Ignoring Sex
Parents
(Female: +) x (Male: SE;VG)
Offspring
Phenotype Number Proportion Ratio
+ 1011 1.0000 1.000
Total 1011
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Chi Square Hypothesis Using Cross #7
Ignoring Sex
Phenotype Observed Hypothesis Expected Chi-Square Term
+ 1011 1.0000 1011.0000 0.0000
Total 1011 1.0000 1011.0000 0.0000
Chi-Squared Test Statistic = 0.0000
Degrees of Freedom = 0
Level of Significance = 1.0000
Recommendation: Do not reject your hypothesis
--------------------------------------------------------------------------
Explanation:
From this data, it is shown that when a fly with wild type crosses with a fly having sepia eye
and vestigial wings, the resulting offspring only has wild type. This evidence can suggest that this
cross is dihybrid cross because in order for the all offspring to have only wild type from parents that
have different characteristics, the cross between the wild type and sepia eye and apterous wing must
be the dihybrid cross. This is shown in the Punnett square below:
SE = Sepia Eyes + = Wild Type VG = Vestigial Wings
Table 9) Punnett Square for a Cross between a wild type female and a vestigial wing / sepia
eye male
SE VG
+ SE+ VG+
+ SE+ VG+
Genotype of the offspring = SE+, VG+
Phenotype of the offspring = All Wild Eye Color / Wild Wing (supported by the result of cross #7)

12. Hyohyun Lee
IB Biology HL: Period 5
April 7th, 2010
12
F2
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Results of Cross #8
Ignoring Sex
Parents
(Female: +) x (Male: +)
Offspring
Phenotype Number Proportion Ratio
+ 561 0.5571 9.508
SE 195 0.1936 3.305
VG 192 0.1907 3.254
SE;VG 59 0.0586 1.000
Total 1007
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Chi Square Hypothesis Using Cross #8
Ignoring Sex
Phenotype Observed Hypothesis Expected Chi-Square Term
+ 561 9.0000 566.4375 0.0522
SE 195 3.0000 188.8125 0.2028
VG 192 3.0000 188.8125 0.0538
SE;VG 59 1.0000 62.9375 0.2463
Total 1007 16.0000 1007.0000 0.5551
Chi-Squared Test Statistic = 0.5551
Degrees of Freedom = 3
Level of Significance = 0.9066
Recommendation: Do not reject your hypothesis
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Explanation:
From Cross #8, it further supports that a cross between a wild type and sepia eye / apterous
wing is a dihybrid cross. As suggested in previous Punnett square, the F1 generation only has wild
heterozygous type. When these heterozygotes cross together, they are expected to produce F2
generation with a phenotype ratio, 9:3:3:1 for wild body color to sepia eye color to vestigial wing
shape to mixture of sepia eye and vestigial wing, as shown in the Chi-Square #8 above. According
the Chi-squared test, the result is not statistically significant because the result is nearly accurate
compared to the expected data and the hypothesized rate. This can suggest that this cross is a
dihybrid cross and this is shown in the Punnett square in next page:

13. Hyohyun Lee
IB Biology HL: Period 5
April 7th, 2010
13
SE = Sepia Eyes + = Wild Type VG = Vestigial Wings
Table 10) Punnett Square for a Cross between two heterozygous flies
++ VG+ SE+ VGSE
++
VG+
++ ++ VG+ ++ SE+ ++ VGSE ++
VG+ ++ VGVG ++ VGSE ++ VGVG SE+
SE+
VGSE
SE+ ++ VGSE ++ SESE ++ VG+ SESE
VGSE ++ VGVG SE+ VG+ SESE VGVG SESE
Genotype ratio of the offspring – ++ ++ : VG+ ++ : SE+ ++ : VGSE ++ : VGVG ++ : VGVG SE+ :
SESE ++ : VG+ SESE : VGVG SESE = 1:2:2:4:1:2:1:2:1
Phenotype ratio of the offspring – 9 Wild type : 3 vestigial-winged : 3 sepia-eyed : 1 vestigial-
winged sepia eyed