Dihybrid Cross Lab Report PDF

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Lab Report includes Abstract, Introduction, Methods, Result and Discussion...

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Alexis Rodriguez Dihybrid cross of mutant and normal traits in Drosophila Melanogaster resulting in F2 generation receiving mutant trait Abstract: The lab was performed to further our understanding of inheritance. We began the lab with eight Drosophila Melanogaster (also known as fruit flies).Four of the flies were mutant males and the other four flies were virgin wild type female flies. The mutation within the male flies were that they had an ebony body color, while the female flies had a normal body color of light brown. The group placed four flies, two male and two female into tube #1, the placed the other four flies into tube #2. This would allow the males and females to mate seeing if the mutation will go to the offspring of Drosophila Melanogaster. The group would then examine the first generation of flies to see if there is a mutation, analyze the data, then mate eight flies again from the first generation to produce the second generation. The group also took into consideration the gender of the flies to see if the male or females had more of a mutation. Throughout the lab many casualties occurred among the flies but many of the flies survived to see the end result. We put the results into Chi Squares to see the relationship of mutation between the flies. Introduction: Genetics by definition is the study of heredity and the variation of inherited characteristics. A gene is the basic unit of heredity. The gene (traits) that the parents carry or express can be transmitted and also be expressed in the offspring. An allele is a specific variation of a gene also known as the genotype. Each organism has two alleles for every gene, one on each chromosome which can either be recessive or dominant. Dominant will always be expressed rather than the recessive. The dominant allele will always have an uppercase letter and the recessive trait will always be

lowercase. For example, if the allele for brown eye color (uppercase B) is dominant and the allele for blue eye color (lower case b) is recessive, the various combinations of genotype and phenotype (physical trait expressed) can be determined using a Punnett square diagram. An organism can be heterozygous, having two different alleles (example: Bb), or homozygous, having the same allele (example: BB or bb). When meiosis occurs, the new cell gets different types of alleles from each parent. Depending on what alleles each parent has, the offspring will have a variation of different traits it has a chance to get. Studying heredity and inheritance is important because you have an understanding of how traits are getting passed on and why certain traits are expressed rather than others. Knowing what traits are dominant and recessive, some predictions can be made for the offspring. Gregor Mendel was an Austrian monk who discovered the basic principles of heredity through experiments in his garden. Mendel's Law of Heredity consist of three principles; the principle of segregation, dominance and independent assortment. The principle of segregation explains that in diploid organisms, chromosome pairs (and their alleles) are separated into individual gametes (eggs or sperm) to transmit genetic information to offspring. The principle of dominance is that the dominant allele completely masks the effects of a recessive allele. A dominant allele produces the same phenotype in heterozygotes and in homozygotes.The principle of independent assortment emphasizes that alleles on different chromosomes are distributed randomly to individual gametes. These processes occur when meiosis is taking place which allows us to make predictions about the offspring. Predictions can be made by using the punnett square and making observations. Drosophila Melanogaster flies were used in this experiment for different purposes. According to the Biological Investigations Laboratory Book Lab Topic 11 Drosophila Melanogaster are small and feed on yeast, so large populations can be kept in small spaces. Drosophila lay hundreds of fertile eggs after mating and produce a new generation in 10 to 14 days, so

results are quickly and easily obtained. Also, the diploid () number of chromosomes in a fruit fly is only eight, which makes it possible to determine on which chromosome a gene for a particular trait is located. The intention for experimenting with these Drosophila Melanogaster flies is to determine their inheritance pattern. Using males with mutations will help keep record of where the mutation goes throughout the offspring. The mutation the males had was an ebony body color while the normal body color is light brown. We made four predictions about what will occur in the two generations of offspring.The offspring generations are distinguished by F1 and F2.1. If the mutant trait was recessive autosomal, than 100% of F1 would be wild and 75% of F2 would be wild and 25% mutant. F1

E

E

e

Ee

Ee

e

Ee

Ee

Phenotype: Light brown body color F2

E

e

E

EE

Ee

e

Ee

ee

Phenotype: EE & Ee- Light brown, ee- ebony color 2.If the mutant trait was dominant autosomal than 100% F1 would be mutant, 75% would be mutant and 25% would be wild. F1

E

E

e

Ee

Ee

e

Ee

Ee

Phenotype: ebony F2 E

E EE

e Ee

e

Ee

ee

Phenotype: EE & Ee- ebony , ee- light brown 3. If the mutant trait was sex linked than 100% males and 100% females would be mutant in F1 and F2 generations. F1

Xe

Xe

Xe

XeXe

XeXe

Y

XeY

XeY

F2

Xe

Xe

Xe

XeXe

XeXe

Y

XeY

XeY

Phenotype for F1 & F2 both male and female- ebony color 4. If the mutant trait was not sex-linked, then 100% of male and female would be wild in both generations. F1

Xe

Xe

Xe

XeXe

XeXe

Y

XeY

XeY

F2

Xe

Xe

Xe

XeXe

XeXe

Y

XeY

XeY

Phenotype for F1 & F2 both male and female- light brown color Method: First, we had to prepare two vials for the fruit flies. To make the medium (fly food) we had to use a 1:1 ratio of drosophila medium to water, and quickly shook each vial until the medium was fully mixed. We had to waited 2 minutes for the medium to set and capped the vial off with a foam stopper. Before we could place the the parent flies (P generation) in the vial, we needed to put the flies to “sleep” by using an anaesthetic

called fly nap. By doing this it made it easier for our group to sex the flies under the microscope. We gathered four mutant males and four wild type females. We placed four flies (2 male and 2 female) in one vial using a brush to transfer them unharmed and the remaining four in the other. We labeling each vial with date and name. The vials then were placed in an incubator set at 22°c for a week giving them enough time to reproduce. Regrouping after a week the group observed the F1 generation to see how many fly offspring there were. To collect the offspring, we again used the flynap to put them under anesthesia so we can take them out of the vials and put them under the microscope to sex them and see if there were any mutations that occurred. We repeated this method to produce the F2 generation. Collecting the data for this experiment we used a Chi-square. A Chi-square is used to find the probability of offspring the P generation will produce and will help us analyze the data. Results: Throughout the four weeks we organized our data using a total of 8 tables. Tables 1,2, and 3 was used to find the probability of the genotypes and phenotypes in the F1 generation. F1 Generation: Table 1. Expected Genotypes: E

E

e

Ee

Ee

e

Ee

Ee

Table 2. Observed numbers: Wild Mutant Total

Male

Female Total

19 0 19

22 0 22

41 0 41

Table 3. Expected Percent of Total: Male 50% Mutant 0%

Female 50% Wild 100%

In tables 4,5,7 and 8 we used the chi-square which is the way to determine if the distribution you observe is likely due to chance or if some factor might be influencing your distribution. To collect the data for the Chi-square you must use the Chi equation : X2 = Σ (O-E)2/E . Where X2 = Chi-Square obtained, Σ = the sum of, O = observed score and E = expected score. F1 Generation: Table 4: Ratio of male and females to what Mendel Expected? Category

Observed

Expected

O-E

(O-E)2

(O-E)2/E

Male Female

Number 19 22

Number 20 20

1 2

1 4 Chi-

.05 .20 .25

Square= Accept? Mendel

Yes Yes

Predicts? Table 5: Ratio of mutants to wild what Mendel expected? Category

Observed

Expected

O-E

(O-E)2

(O-E)2/E

Wild

Number 41

Number 41

0

0

0

Mutant

0

0

0

0 Chi-

0 0

Square= Accept? Mendel Predicts?

Yes Yes

Discussion The hypothesis that our data supported was, if the mutant that was recessive autosomal, then 100% of the F1 flies will be wild. It also supported that the F2 flies would be 75% wild but, 25% of the F2 flies would be mutant. In order to form that hypothesis we set up a Punnett square. To test the hypothesis, mated the male mutant and female wild type flies in 2 vials then put each generation under the microscope to see how many had an ebony body color (the mutation) and how many had a light brown body (normal) and it did support one out of the four hypotheses we made. The only problem with our experiment was at the second vial of P generation died and didn’t reproduce any offspring. An explanation for this could have been that we mis sexed the flies and put two males in the same vial, or when we were transferring the flies into the vial they could've gotten stuck in the medium. Literature Cited: -Biological Investigations Form, Function, Diversity and Process (Dolphin and Vleck., 2015). - Biology (Raven et al., 2017)....