Drosophila Melanogaster

Testing Gene Inheritance in

(Drosophila melanogaster)

AP Biology

May 11, 2011

ABSTRACT

Drosophila melanogaster is used in this experiment due to its relatively simple genetic make up. To test the principles of Mendelian genetic inheritance, Drosophila melanogaster were used. Four tests were conducted and a number of three hundred flies were counted for each cross. This enabled a Chi Square test to take place to compare the amount of error by chance and also to evaluate correct ratios from the predicted ones. The results of this experiment support to some extent the hypotheses predicted by using the Punnett square and Mendelian principles.

Introduction

Drosophila melanogaster is a small common fly that has been used in genetic

recombination due to the fact that it has simple food requirements, is hardy, completes its

life cycle in 12days, occupies little space, can be knocked out easily, makes a large

number of offspring, and it has many types of hereditary variations that can be seen with

low power microscopes. This put the fruit fly on the front lines of genetic research.

Drosophila melanogaster is one of the few organisms where the whole genome is known

and an abundant amount of genes have been identified.

Drosophila melanogaster is small and easily handled but large enough to see through a microscope. They can be anesthetized and manipulated with unsophisticated equipment. It is easy to differentiate the sexes of Drosophila melanogaster because they are sexually dimorphic which means that males and females are different, thus making it easy to differentiate the sexes. They have a short generation time of about 10-12 days and do well at room temperature. (Miller)

Gregory Mendel did pioneering work in the field of inheritance. By using the garden pea pod plants, he discovered seven basic characteristics of the plants, establishing three basic laws. The first law is a sex cell may contain two different traits, but only one will show through. The second is the basis for dominant and recessive laws, which includes that characteristics are inherited independently from another. The third law is that each characteristic is present because of genes, one from each parent. A recessive trait is one that will not show up unless two recessive traits come together from each parent. A dominant trait is a characteristic that will always be present if inherited. Mendel also was the first one to use genotype, phenotype, and to use heterozygous and homozygous as a naming process. Genotype is the genetic make up of the individual for that particular characteristic. Phenotype is the name giving to the outward appearance of the characteristic. The term heterozygous describes an individual who carries both the dominant and recessive traits. Homozygous is term to describe an individual who carries either all dominant or all recessive traits.

Drosophila melanogaster has many dominant and recessive characteristics. A sex-linked mutant recessive trait white eyes use the symbol (w), while wild red eyes use the symbol (w+). Sepia eyes is an autosomal (non-sex-linked) mutant recessive trait and this is identified by the symbol (se) while wild red eyes use the symbol (se+). Brown eyes are an autosomal mutant recessive trait, identified by the symbol (br) while wild red eyes is identified with (br+). Black body is an autosomal mutant recessive trait that is identified with the symbol (b) while the color of a brown body is identified with the symbol (b+). Vestigial wings are an autosomal mutant recessive trait that is identified with the symbol (vg) while wild normal wings is identified with the symbol (vg+). The apterous condition, resulting in a lack wings is an autosomal mutant recessive trait that is identified with the symbol (ap) while wild normal wings are identified with the symbol (ap+).

In the experiment it was hypothesized that if the first cross (P- meaning parental), between 6 wild normal winged males (6 vg+ ap+) with 6 apterous females (6 ap ap) would result in a all F1(first generation) progeny with wild wings. The second hypothesis consisted of if the second cross P between 6 sepia eyed wild normal winged males (6 se se vg+ vg+) x 6 wild normal eyed vestigial winged (se+ se+ vg vg) then all of the F1 progeny would result in wild dominant traits. The third hypothesis is that if the third cross P between 6 wild red eyed females (6 Xw+ Xw+) x 6 white eyed males (6 Xw Y) then the F1 progeny would result in 1:1 ratio of red eyed female and red eyed male. The fourth hypothesis consisted of if cross 4 between 6 heterozygous males for yellow body, normal wings, and red eyes (b+ vg+ br+ b vg br) x all homozygous recessive for black body, vestigial wings, and brown eyes (b vg br b vg br) then the resulting progeny should be (b vg+ br+ / b vg br), (b+ vg br+ / b vg br), (b+ vg+ br / b vg br), (b vg br / b vg br), (b+ vg+ br+ / b vg br), (b vg br+ / b vg br), (b+ vg br / b vg br), (b vg+ br / b vg br). These resulting ratios are from Mendelian concepts of dominant and recessive traits. (McClean)

The fifth hypothesis consisted of if cross 1 F1 between 6 heterozygous apterous males (ap+ ap) x 6 heterozygous apterous females (ap+ ap) then the resulting progeny would consist of a 3:1 phenotypic ratio ¾ wild; ¼ apterous. The sixth hypothesis consisted of if cross 2 F1 between 6 heterozygous males for wild eyes wild wings (se+ se vg+ vg) x 6 heterozygous females for wild eyes wild wings (se+ se vg+ vg) then the resulting progeny of F2 would be a 9:3:3:1 ratio. Our seventh hypothesis consisted of if cross 3 F1 between 6 heterozygous females (Xw+ Xw) x 6 wild red eyed males (Xw+Y) then the resulting progeny would be ½ red eyed females, ¼ red eyed males, and ¼ white eyed males.

Materials and Methods

Drosophila melanogaster were used in our experiment to understand Medelian genetics and inheritance of traits. The flies were kept in four plastic vials and were hindered from escaping by placing a sponge at the open end. Powdered food was then placed at the bottom of the vials with equal parts of distilled water. Ten grams of yeast was added after the mixture was made to help with the food process. Plastic nets were placed in the vials so the flies