Bio 103, Lab 9: Mendel's Garden Revisited

Paul Grobstein's picture

One central piece of modern biology derived from Darwin's voyage to the Galapagos in the latter part of the 19th century. A second emerged, more or less independently, during the same period and resulted from the work of Gregor Mendel breeding pea plants and carefully observing the results. This work produced the first clear understanding of "laws of inheritance", and remains fundamental to most modern understanding of genetics.


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://www.biologylabsonline.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 monohybrid cross, as well as some that yield unexpected results in a dihybrid cross. For the latter, be sure you have fully understood the behavior of each trait in monhybrid crosses first.

Anonymous's picture

fruit fly lab- think it is impossible

i need help with this lab, i don't think it is possible for the results.

the p1 sepia is female and the p1 male is wild.
the cross is sepia(brown) x wild (red). i have in the f1 3 red male, 3 red females, 1 brown male , and 0 brown female. in the f2 i have 52 red males with wings and 3 red males without wings. The female red with wings are 47and without wings it is 7. The male brown is 24 with wings and 3 without wings. The female brown is 26 with wings and 2 without wings.

how could the traits be inherited and what could be the type of inheritance. what kind of explanation can you give of the statistics. what would the punnett square look like because i cannot justify any of the data.
is it autosomal, dominant, recessive or sex linked?
thank you very much.

LaKesha's picture

FLIES AND THEIR COLORS (LaKesha, Sharhea, Shanika)

We decided to observe the effect in eye color in the fly lab. We were a little lost at first because we concentrating more on a dihybrid cross before a monohybrid cross. We finally settled on the eye color with the wild type body. We found that most eye colors were recessive and the wild type was dominant. We observed brown, sepia and purple, which turned out to be recessive. The only color that was totally different was the white eye color. They were sex linked and recessive. When the females had white eye color and the male was a wild type, they created females as wild type and males that had white eyes. When we switched and had males with white eyes and females with wild, the offsprings were all wild type.
ekoike's picture

Mendelian Flies

Crystal, Luisana, and Eri

In general, we were trying to find how and whether sex linked breeding had an effect on the population. We initially believed that the breeding population will follow the Punnett squares that we constructed and the homozygous dominant (TT) would more often than not mask the recessive traits.

However, after several trials using different genes that yeilded results matching the punnett squares that we drew out as predictions, we came across a combination that broke the pattern. We had crossed a curly winged (CY) female with a wild type male (+) which gave 50/50 offspring. However, when we bred heterozygous flies, we found that instead of the expected 3:1 ratio, the breeding yeilded 2 curlywinged flies, and 1 wild type fly. In other words, the curly wing gene turned out to be the dominant. Furthermore, the fly that would have been homozygous dominant did not appear - CY is a lethal dominant resulting in the abortion of that offspring.

eharnett's picture

he's so fly

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:

XYB XYB

X+ XYBX+ XYBX+

Y XYBY XYBY

F2:

X+ XYB

XYB XYBX+ XYBXYB

Y X+Y XYBY

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.

 

ekim's picture

on monohybrids.

Vivian Cruz, Saskia Guerrier, Eurie Kim

Hypothesis
We expected that we would always find true breeders in whatever traits were crossed over and that the ratios of different traits (recessive, dominant) would follow the Punnett Square ratio.

Observations
EYE COLOR.
1) Brown --> Brown = 100% brown
2) Wildtype --> Brown = 100% wildtype
3) F1 --> F1 = 75% wildtype, 25% brown

ANTENNAE.
1) Aristepedia --> Aristepedia = 33% wildtype, 66% aristepedia
2) Wildtype --> Aristepedia = 50% wildtype, 50% aristepedia
3) F1 --> F1 = 100% wildtype

Our Story
From looking at the observations, we can tell that in the eye-color traits, brown is the recessive gene. However, in the antennae traits crossover, we see a problem.  It does not follow the ratios of the Punnett Square.  First of all, when we crossed over both aristepedia-antennae types, we ended up with some wildtypes.  But how so?  This means the parents must have had a wildtype gene, which then results in children being wildtypes.  But at the same time, if the parents had wildtype genes, the ratio should've been 3:1 (aristepedia : wildtype), but instead it was 2:1.  This means that not only is the aristepedia antennae type a dominant gene, but there are no 100% aristepedia-antennae-typed genes.  Therefore, the aristepedia trait only exists as heterozygotes.
(According to Wil, the aristepedia trait is a LETHAL DOMINANT GENE.)

cmcgowan's picture

the podfather

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.

kharmon's picture

Mendel Revisted

From the observations that we made as a class, we concluded that "expected" results will only be yielded when the breeding is true, when the trait is crossed with the wildtype and all the offspring are wildtype (in F1), and when it doesn't matter if the male or the female possesses the trait. The trait that we chose to observe was curly wing shape, and it was an anomaly and did not adhere to Mendel's rules. When we crossed a curly winged female with a wildtype male, we got a 2:2 ratio of curly to wildtype instead of the expected population of all wildtypes. We then crossed a curly winged male to a wildtype female, to ensure that the possession didn't matter, and we found a similar 2:2 ratio. We concluded from this that our starting point must not have been homozygous and we began testing punnett squares to determine our starting genotypes. After 2 tries, we decided that curly wings are a dominant trait and wildtype is recessive. So in our initial cross, we the wildtype male had a ww genotype and the curly winged female had a heterozygous Cw genotype. The results produce 2 Cw to 2 ww offspring which phenotypically is 2 curly to 2 wild just like our results. To prove this, we crossed two curly winged flies and found a 2:! ratio of curly to wild. The punnett square that we determined from these results was Cw x Cw which yielded CC, Cw, Cw, and ww. As the ratio was 2:1 instead of the expected 3:1, we speculate that the CC genotype is lethal and that all curly winged flies then have a Cw genotype like in our two previous punnetts. Given more time, we would have liked to test several other traits to find out which other traits didn't follow Mendel's rules and why.
Kendra's picture

Mendel Lab

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.

Catrina Mueller's picture

Fly Fun!- Catrina, Kate, and Rachel

We first crossed purple eye with wild type and found that F1 was all wild and f2 was three to one (wild to purple). That meant that the f1 cross acted in the way we predicted it to.

We then crossed a female singed and a male wild.

F1: female-100% wild

male-100% singed

F2: female- 50% wild, 50% singed

male- 50% wild, 50% singed

We think that singed is an X-chromosome linked trait, the F1 males having received their X-chromosome from the singed female (P). Perhaps it is an x-linked recessive trait?

We then crossed wild type and curly wing type. We found a 50/50 ratio between wild and curly in both genders.

We then crossed curly type and curly type (from F1) and came up with a weird answer. The ratio was 2:1, curly to wild, meaning that curly was dominant over wild type.

We started a new cross, curly and curly, and came up with the same ratio of 2:1, curly to wild. This suggested that curly is a heterozygous trait, homozygous curly being lethal.

Samar Aryani's picture

Samar and Ruth-Tan Plan

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.

MarieSager's picture

one curly, one wild 2

one curly, one wild

2 curly, 2 wild 1:1 ratio

mated male curly with female straight= 2 straight 2 curly

mated curly with curly= 2 straight and 2 curly

2 curlys again = 1 wild, 1 wild, 2c, 2c (ratios)

THIS VIOLATES THE RULES!

why?

Well, we then explored the characteristic of true breeding and mated a male curly with a female curly. And found that there was a 2 (curly) : 1 (wild) ratio. Therefore, we hypothesized that culry wings are a recessive trait, and even more, if the genes start off as homozigous, then there will not be a 3:1 ratio. This is also true for starting with wild wings, because if you mate two wild winged flies, you will also NOT get a 3:1 ratio.

We then tried some other combinations, but many of these had 3:1 ratios.

randomness