In this lab you will be invited to participate yourself in making the kinds of observations and inferences that Mendel made. We will do so together studying not pea plants but fruit flies, and using not live animals (for which the studies would take weeks or months) but a computer simulation which is quite realistic in most important characteristics. The simulation, called FlyLab, is available to registered individuals (students in this class) at http://biologylab.awlonline.com.
After we've worked through some of the basic observations together, you should work in pairs to make observations yourself on some fly traits other than those we have explored together. Your task is to "make sense" of your observations starting with the basic ideas we develop together and adding whatever additional ideas seem necessary. Try and find some traits that yield unexpected results in a monhybrid cross, as well as some that yield unexected results in a dihybrid cross.
50% white eyes
50% red eyes
*two flies appeared on the screen
Second Generation: (used two flies from first generation)
50% white eyes
50% red eyes
*four flies appeared on the screen
Third Generation: (used top two flies from second generation, both had red eyes)
75% red eyes
25% white eyes
*the white eyes only appeared in the males in this generation.
For my second cross, I used a female with spread wings (D) and a black body and a wild type male.
50% closed wings
50% open wings
75% wild type bodies
25% black bodies
75 % wild type bodies
25% black bodies
HYPOTHESIS: Some traits do not follow the general ratio of 9:9:3:1. Some traits may not be able to be expressed at the same time (such as open wings and black bodies). Also, some traits may be muted in a sex (as in the case with females and white eyes).
Because I wrote my hypothesis after I performed the experiment, my hypothesis seems to follow the data. However, I don't know why this is true. Why could first and second generation females have white eyes but not third?
- exhibits true breeding
- is not more dominant than "wild type" wing angle. Starting from the first generation of offspring, there was a 1:1 ratio of each wing angle.
- is not gendered. Both males and females exhibit the trait at the same frequency
- exhibits true breeding
- is recessive in relation to the "wild type" eye shape. In the first generation of offspring there were no phenotypically eyeless flies, in the second there was a 2:1 ratio of eyes to eyeless. In subsequent generations, whether or not there were eyeless flies depended on whether or not we selected a phenotypically eyeless parent.
- is not gendered.
Dicheate wing angle and eyelessness do not seem to have any impact on one another. When we bread an dicheate mother with wild type eyes and an eyeless father with wild type wings (and vice versa), each trait appeared with the frequency that would be expected based on the earlier experiments.
First Generation: Female (white eyes) Male (wild)
Second Generation: Female (wild) Male (white eyes)
Given that the white eyes appeared in the first process of mating, white eyes are clearly not a recessive trait in the male of the second generation, but is in the female of the first generation. We concluded that the white eyed trait is sex-linked since it turns up to be neither a dominant or recessive trait.
Third Generation: 1 Female (wild) 1 Male (wild)
2 Female (white) 2 Male (white)
Throughout the three generations the ration of wild to white is 1:1. In the last observation, only one of the males turned up with white eye. Yet we had to take in account that the female that turned up white in the Second generation still carried the white eyed trait from the first generation. We assumed the same for the males.
+ (wild type): 552
PR (like the mother): 204
M (like the father): 192
PR, M (combination of the mother and father traits): 64
These results yielded an approximate ratio of: 9:3:3:1
These were the expected results based on two parents with traits that we determined to be true breeding.
We discovered that the wing trait of Dicheate, where the wings are spread apart, was not true breeding. Any combination of breeding, over numerous generations, yielded a mysterious disappearance of the trait. This confused and baffled us. We determined that perhaps there is something inherent in the definition of "not true breeding" that allows traits to completely disappear or appear completely randomly.
Does a not true breeding trait mean that it is a mutation of a gene and cannot be inherited in the same statistical way that 'normal' genes are?
1002 flies -all lobe eyed w/ wildtype wings
we assumed that lobe eyes might be dominant, and that the female parent was homozygous(LL). To prove this, we checked to see if the lobe eyed trait was a true breed. and it was! :)
The male's apterous wings were also proven to be true breed.
Next we crossed the offspring of our lobe eyed female and apterous male. (lobe eyed wildtype) w/ the following results out of a total of 998 flies:
723 lobe eyed wildtype wings(ratio:21.265)
206 apterous wildtype eyes(ratio:6.059)
35 lobe eyed apterous(ratio:1.029)
For a second experiment we crossed a female with apterous wings and a male with lobe eyes.
For this experiment we got very similar results, which we could infer from that there are no sex linked traits.
Lobe eyes must have been dominant over wildtype eyes. And the apterous is a recessive gene. Both are homozygous.
We DO NOT have an explanation for why we hae such peculiar ratios.
Parents + and CY --> F1 50+ and 65CY i.e. 1 : 1.3 ratio
This fairly equal distribution suggests that + is not dominant over the CY. In fact, a greater proportion of offspring are CY phenotypes, but dominance is not total.
I crossbred a new pair of flies, CY and CY. Based on the assumption that they were homozygous, I predicted that they would produce offspring that were all CY in phenotype.
Parents CY and CY --> F1 32+ and 79CY i.e. 1 : 2.47 ratio
Subsequent crossbreeds of two CY offspring produced the following +:CY ratios
1 : 1.81
1 : 1.842
1 : 1.941
1 : 1.872
This implies that CY is not a homozygous phenotype. It is possible that one of the two variants that make up CY is recessive to +, and the other variant is dominant over +. This would help explain the first set of results in the crossbreed between + and CY.
Tan Female and Wild Male
504 Wild Female
WIld Female and Tan male
262 Tan male
271 Tan Female
257 Wild Male
266 Wild Female
Wild Female and Wild Male
514 Wild Female
243 Wild Male
249 Tan Male
Wild Female and Wild Male
508 Wild Female
521 Wild Male
When there is a tan female the tan gene appears in the male in the first offspring. We then crossed a wild female and a tan male and you had a 50% chance of getting a tan offspring in both the male and females. We then crossed a wild female and a wild male and we got the tan gene appeared only in the males but most of the offspring were wild type. When we crossed another wild female and another wild male, the tan gene disappears and you only get wild offspring. In other words, the tan gene disappears in the fourth generation. It is interesting to note that in the 3rd generation there were no tan females.
It seems that the variations present in the parent or parents increase the chances for the traits to take on the dominant gene in the offsprings.
Female (tan body) + Male (wild)
-> Female (228 wild) + Male (228 wild)
-> Female (255 tan) + Male (264 tan)
-> Female (473 tan) + Male (512 tan)
-> Female (477 tan) + Male (508 tan)
Tan body: dominant trait
Female (curly wings) + Male (purple eyes)
-> Female (257 W) + Male (218 W)
-> Female (271 C) + Male (240 C)
-> Female (175W) + Male (160 W)
-> Female (76 P) + Male (92 P)
-> Female (239 C) + Male (200 C)
-> Female (25 PC) + Male (32 PC)
-> Female (158 P) + Male (176 P)
-> Female (327 PC) + Male (328 PC)
Conclusion: Our hypothesis was proved right since in each experiment the offspring took on the variant traits. In the first experiment, the offspring showed to have tan bodies just like the female parent at the beginning of the chain. In the second experiment, the traits surface in further generations simultaneously in both sexes. Therefore, not only are the variant traits passed on to future generations, but also become more apparent as the chain progresses.
For our next experiment, we mated a yellow-bodied female with a wildtype-bodied male. In the F1 generation half of the offspring were yellow and half wild-type, unlike the other experiments we performed, where all offspring were wild-type.
To ensure that it was not another type of variable we tested a yellow-bodied female with a yellow-bodied male, and offspring in three generations to follow were all yellow-bodied, this led us to conclude that yellow-bodiedness is in fact a pure-breeding trait.
Upon further review of our results, we realized that only the males were yellow-bodied, which would mean that the yellow body color gene is sex-linked.
p pp(purple) p+ (red)
+ p+ (red) p+ (red)
This supports the idea that the combination of two genes from two parents leads to four possibilities in each generation. In the F1 generation, because every offspring got one purple gene from the mother and one wild type gene from the father, they all had the same combination of one p and one +. In the next generation, though, offspring could inherit a p or a + gene from either parent. So one possibility was pp, one was ++, and the other two were +p. The phenotype of the +p genotype in the F2 generation would reveal which of these genes overrides the other. We found that 3/4 of the F2 generation had the wildtype phenotype, so we concluded that + was the gene that overrode p.
Purple, regular shaped + Purple, star shaped
Yielded half Purple, regular shaped and half purple, star shaped again.
Purple, regular shaped + purple, regular shaped
Yielded all purple, regular shaped
Purple, star shaped + purple, star shaped
Yielded 1/3 purple regular shaped and 2/3 purple star shaped.
When we isolated the eye shape gene and disregarded the eye color gene, the resuts of the cross
Star shaped + star shaped
still yielded this 2:1 ratio. So the fact that our results were the same when the two traits were isolated says that eye color and eye shape are not related in their inheritance. However, we do not know how to account for this 2:1 ratio when crossing eye shapes. We found this ratio odd because when we crossed flies with different eye colors, we came up with a 3:1 ratio in phenotype in the first generation, and either a 1:1 or 1:0 ratio in the second generation. We think that in order for this 2:1 ratio to occur there must be some other factor contributing to the flies' inheritance of eye shape.
Given that these results were a bit different from the all same/3:1 ratios that we saw in the earlier examples, I decided to test whether or not curly-wingedness was a true-breeding characteristic:
2nd cross: CY male and female
F(1): 50% CY, 50% +
F(2): 50% CY, 50% +
F(3): 50% CY, 50% +
Hypothesis: In a monohybrid cross, a trait that is characteristic of one of the parents that does NOT appear in F(1) is a true-breeding characteristic; conversely, a trait characteristic of one of the parents that DOES appear in F(1) is not a true-breeding characteristic.
First I bred a tan female fly with a wildtype male fly.
F1- 1 female wildtype, 1 male tan
F2- 2 wildtypes, 2 tan (1 male and female of each)
bred male and female tan
F3- 2 tan (1 female tan, 1 male tan)
Next, I bred a female wildtype with a shaven male.
F1- 2 wildtypes
F2- 2 wild types, 2 shaven
bred 2 shaven
F3- 2 shaven
So, I can conclude from my results that tan coloring and shaven are true breeding traits since when I bred 2 tan flies or 2 shaven flies together the offspring continually showed these traits and no others.
Hypothesis: There is equal chance for the offspring to have either father or mother traits.
Mother: Wild type (+) Father: Curly Wings (cy)
females + 271, Male + 247
females (cy) 271, Males (cy) 243
Second generation incest:
Mother (cy) father (+)
females: (+) 253 Males (+) 241
females:(cy) 238 Males (cy) 268
Our hypothesis seems to have proven correct as we came to see that in only changing one trait in the original parents, offspring were equally likely to have curly wings or wild type bodies.
As for the second generation we saw that characteristics equally carried through to the third generation.
There were variations but they were probably insignificant.
We very much enjoyed taking on the brain and logic of Mendel. We mated every "weird" thing with the wild type and they only produced about five offspring. Why were there no babies?
We hypothesized that either dichaete-winged or wildtype would be a dominate gene, and whichever was not dominate would be recessive.
We bred a dichaete-winged fly with a wildtype fly. These flies produced an f1 generation of 50% dichaete-winged and 50% wildtype. This continued for all subsequent breedings involving one dichaete and one wildtype.
We did two types of breeding variation once this constant was found. For our first variation, we bred two dichaetes. We ended up with a ratio of 1 wildtype: 2 dichaete. This pattern remained constant when we continued to breed two dichaete from each subsequent generation.
For the second variation, we bred two wildtypes after the initial hybrid breeding. Our f2 generation consisted of all wildtyped. As two wildtypes were continuing to be bred, the dichaetes did not reappear.
Our results were not true to our hypothesis. Neither gene stood out as either recessive or dominate but we do not know why these results occurred.
Key: W = wild eyed; P = Purple eyed
Rule #1: Breed W with P whenever possible (whenever both w and p exist among offspring).
Rule #2: Breed W whenever possible.
Rule #3: Breed P whenever possible.
Test #1: Applying Rule #1
and follows with breeding as 1:1
Test #2: Applying Rule #2
and follows with breeding as 2:0
Test #3: Applying Rule #3
and follows with breeding as 0:2
The interesting occurance was that consistancy with seeing just wild type in test two (which was what we were looking for) arrived by trial F4. But the consistancy of seeing just purple in test 3 (which was what we were after in that test) arrived earlier, in the F3 breeding. This lead us to infer that the red contains something thats holds on to a "hiddenpurple " longer. While the purple does not hang on to a red trait for any length of time.
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