Bio 103, Lab 9: Mendel's Garden Revisited

Kaitlin Cough, Elizabeth Harnett

First Experiment: Monohybrid Cross

In this experiment we crossed a wild type male with a yellow bodied female. In the F1 generatio, we found that the ratio was 1:1, but the trait had switched: the females were all wild type, whereas the males were yellow bodied. We found this odd and thought, maybe it's sex linked? Then we looked at the F2 generation and found a 1:1:1:1 ratio. 25% females were wild types, 25% females were yellow bodied, 25% males wild type, 25% males yellow bodied. We then determined that yellow bodies was indeed a sex linked trait and that it was recessive.

F1:

X^YB X^YB

X⁺ X^YBX⁺ X^YBX⁺

Y X^YBY X^YBY

F2:

X⁺ X^YB

X^YB X^YBX⁺ X^YBX^YB

Y X⁺Y X^YBY

In our next experiment we wanted to try a dihybrid cross, however caused us a lotof trouble. We wanted to cross a wild type female with a curly winged and aristepedia antenae male fly. However, when we crossed them we found that our F1 generation had a 1:1:1:1:1:1:1:1 ratio which seemed rather odd. We decided to focus on the aristepedia atenae trait first.

We then then did a cross between a female heterozygote and a male heterozygote (for the aristepedia antenae trait) , this was our Punnet Square:

AR +

Ar ARAR Ar+

+ Ar+ ++

We had found before that the ratio was only 2:1, when it should have been 3:1 (like the Punnet square above). We determined that the AR homozygous dominant trait was lethal and that is why the ratio changed.

Andy, Rachel and Caitlin McG 

We tested curly and a wildtype and it was 1:1 and then we tested a f1 curly with another f1 curly and we got a 2:1 ratio which made use confused because it didn't fit with the Punnett square we created. According to the Punnett square, the ratio should have been 3:1. When we were trying to figure why this was, we decided to test 2 completely new curly flies thinking that because they were the same type, they would be true breeders and yield all curly offspring. However, the ratio was 2:1 again. This lead us to believe that the curly flies are heterozygous which means that curly is dominant but has to posess a wildtype gene in order to exist. The CYCY produced by the Punnett square cannot actually exist in reality, thus leaving only 3 possibilities ( 2 of which are CY+ and thus the same.) This why breeding 2 curly yields a 2:1 ratio.

In our second experiment our phenotype was eyelessness. First we crossed 2 eyeless flies which yielded all eyeless flies, which means that they are true breeders. Then we crossed 1 fly with eyes and 1 eyeless fly. All offspring had eyes, which led us to hypothesize that the eye-having gene is dominant. We predicted that their offspring would produce 3 wildtype for every 1 eyeless fly. To test this, we crossed the eye having offspring, which yielded a 3:1 ratio, just as we had predicted because we are amazing scientists.

Kendra and Ashley

In this lab, we had to conduct the same experiments as Mendel, but using a computer program. We had to find a gene that didn't prove the 3:1 ratio correct. When we tried to cross a brown eyed/wild type female with a wild type male, we found that the brown eyed trait was recessive because in F1, both the female and the male were wild type but in F2, the offspring still showed a 3:1 ratio, which means that this trial did not prove Mendel's experiment wrong.

So then we decided to try out the body color of the fruit flies. We made the female a yellow/wild type and left the male as just wild type. In F1, we found that it was a 50/50 split between the wild typed bodies and the yellow wild typed bodies, only this time the males were yellow bodied. Then, in F2, we found that some of the offspring came out wild type and some came out yellow typed but more of the offspring were yellow typed. From this we concluded that the yellow bodied/ wild type was dominant over the wild typed body. We also found that yellow bodied/wild typed flies breeded true, which means that the yellow body was dominant over the wild type.

So, we think that the genotype is yellow bodied, since the parents were both wild typed but just the female was yellow bodied. Because all of the offspring were overall wild typed and the most were yellow bodied, we think that yellow body must be the dominant genotype.

We tested body color for our experiment. We decided to start off with a wildtype male and a tan female. The offspring were equally split with half tan males and half wildtype females. We then mated the offspring of the F1 generation and it resulted in an equal number of tan and wild males and females. At this point we came up with a hypothesis.

According to Mendel, there are two genes for each trait. However, it appears that males have only one gene that accounts for body color. We think that the gene for body color is carried on the "X" chromosome. Males, possessing an "X" and a "Y" get the gene from the mother, who possesses two "X" chromosomes. The females acquire one "X" from their father and one "X" from their mother, the tan is covered up by the wild. Thus, females can carry the tan trait recessively. We think that tan is an x-linked recessive trait.

To test this, we mated a tan male and wild female and hypothesized that the F1 generation would be one wild male and one heterozygous wild female. We would then be able to mate that female with a new tan male and have evenly split wild and tan offspring as in our previous trials. This proved to be the case, thus validating our hypothesis and making us the most amazing people in the world.