cross lab test on drosophilia

The aim of this lab investigation was to look at how the drosophila melanogaster fly inherits those characteristics. The experiment was carried out to better understand the relationship between the ratio of phenotypic traits in two generations and the presence or absence of a genetic trait in an organism. When two individuals from F2 phenotype generation are crossed in a hybrid cross, the outcomes are predicted to be 9:3:3:1. In this phenotype ratio, the dominant traits were regular wings and red eyes, while the recessive traits were recessive wings and black eyes. From the results obtained, while following the laws of Mundelein genetics, the 9:3:3:1 phenotypic ratio could have possibly been created from the phenotype ratio of 3:1 expressed in the Dihybrid cross. The results enabled us to prove that the unknown F1 generation has the phenotypic ratio of 3:1 of the dominant phenotypes that are normal winged and red-eyed. The phenotypes discovered were proved to be carrying the recessive alleles of vestigial wings and black eyes observed as (RrWw x RrWw).

The calculated chi-square was found to be 10.48> the critical chi-square of 7.82 where the P-value>0.05. Therefore, the null hypothesis was rejected since the calculated chi-square value (10.48) was less than the critical value (7.82) and the p-value was greater than 0.05.

Introduction

Drosophila fly has been one of the most favored species for carrying out genetic research for the let centuries (Peter). This is mainly because it can be captured easily in the lab settings. In addition, the abundance of offspring a female drosophila is capable of producing in the shortest period and the lifespan of two weeks maximum are the most reasons as to why this fly is favored for genetic studies. Its genetic components are also significant for genetic research. Drosophila has four chromosome pairs. These pairs include the three autosomal chromosomes and the X/y sex chromosomes (Peter).

Therefore, understanding the fly genetics helps the genetic researcher to apply the similar ideology and understand the same genetics found in other species. Drosophila has many mutant variations whereby the mutations range in body pigment, eye pigment, wing shape, or size and body bristles (Ilona).

For this experiment, we worked with the three-body color mutations. The four chromosomes of Drosophila melanogaster were all mapped out indicating the position of its mutation chromosome. In this experimental research design, we would expect to see 3:1 phenotypic ratio from the F2 generation and no phenotypic ratio from the F1 generation because they are all the same genotype.

Materials and methods

During the process of experimental setup, the two culture test tubes were prepared with each test-tube specified for specific crosses. By doing so, we prepared the culture tubes for the drosophila flies to produce offspring, live and reproduce offspring. Later on, we created a high carbohydrate and yeast media (Radlick). In preparing the media, we added a cup of fly media to one cup of water in each culture tube. The solution was stirred thoroughly and formed into a solid state.

A grain of yeast was added to each culture tube and the tube was closed with a sponge stopper. However, when adding yeast, one must be careful to avoid adding excess yeast that can lead to overproduction of toxic carbon dioxide.

The punnet squares were used to predict the inheritance following the basic steps. The parental cross was set up based on the hypothesis to check if the cross was monohybrid or Dihybrid. The F1 and F2 generations on the parental cross were created and analyzed the phenotypes were placed in each Colum as shown below.

The monohybrid cross

The Punnet squares below shows the expected F1 and F2 offspring from a monohybrid cross between PP and pp parents. In this experiment, we would expect to see 3:1 phenotypic ratio from the F2 generation and no phenotypic ratio from the F1 generation because they are all the same genotype.

F1 expected frequency: F2 expected frequency:

P

P

P

Pp

Pp

P

Pp

Pp

P

P

P

PP

Pp

P

Pp

Pp

The Dihybrid Cross

The Punnet squares below shows the expected F2 offspring from a Dihybrid cross between PPSS and PPSS parents. In this investigation, when we crossed two individuals from the F2 generation in a Dihybrid cross, we expected to find a phenotypic ratio of 9:3:3:1

Gametes

PS

Ps

Ps

Ps

PS

PPSS

Ppss

Ppss

Ppss

Ps

Ppss

Ppss

Ppss

Ppss

Ps

Ppss

Ppss

Ppss

Ppss

Ps

Ppss

Ppss

Ppss

Ppss

Results

Corn Monohybrid Chi-square Analysis:

Phenotype

Purple

(dominant)

Yellow

(recessive)

Total

Observed (O)

1011

373

1384

Expected (E)

1038

346

1384

O-E

-27

27

NA

(O-E)2

729

729

NA

(O-E)2/E

0.70

2.11

2.81

DF=1 critical chi-square=3.84 Calculated chi-square=2.81

Calculated chi-square of 2.81 < critical chi-square of 3.84. P-value > 0.05. Thus, our null hypothesis is true and our observed phenotypic ratio represents our expected phenotypic ratio.

We will accept the null hypothesis.

Corn Dihybrid Chi-square Analysis

The table below shows the Drosophila Lab Class Data obtained from the experiment, which was under investigation.

Degree of Freedom=3 critical chi-square=7.82 calculated chi-square=10.48

Discussion and conclusion

In this lab activity, we were determining how the traits are inherited in drosophila fruit fly by crossing the flies. Each parent produced gametes that have genetic materials carried on to the chromosomes (Klug 56). A combination of the produced gametes formed a zygote responsible for trait inheritance. The wing shape and eye color were found unrelated. In other words, the gene for the eye color is coded on a different chromosome. The red eyes were discovered to be the dominant traits and the purple eyes became the recessive traits. The female drosophila was found to possess the normal wings and the heterozygous eye color whereas the female drosophila was found to be having the homozygous for wing shape and the purple eyes.

The calculated chi-square of 10.48 >critical chi-square of 7.82 and the P-value > 0.05. Thus, we reject our null hypothesis because our calculated chi-square value (10.48) is less than the critical chi-square value (7.82) and our p-value was greater than 0.05.

Therefore, the deviation between the observed and expected phenotypic ratios is due to something other than chance. Our observed phenotypic ratio does not represent the expected phenotypic ratio.

Work cited

Geiger, Peter. “An Introduction to Drosophila Melanogaster.” An Introduction to Drosophila Melanogaster; Arizona Universtiy, 2002 Web. 07 May 2016. .

Miko, Ilona. “Thomas Hunt Morgan and Sex Linkage Skitable”. Nature Education, 2008. Web. 06 May 2013. http://www.nature.com/scitable/topicpage/thomas-hunt-morgan-and-sex-linkage-452.

Klug, William S., and Sarah M. Ward; Essentials of Genetics. Boston: Pearson, p.30-100, 2013 Print

Radlick,L. Analyzing Eye Pigment Mutations In Wild and Mutant Strains Of Drosophila.

BIOL 1010. Spring, 2011.