Genetics Lab Fruit Fly Unit File Part Two Fall2023 (1)(2)

General Genetics Laboratory UHD Name _________________________________________ Unit File: Fruit Fly Experiment By Dr. Yuanyuan Kang, Mr. Mehdi Esmaeiliyan, Dr. Meghan Minard Summary The purpose of this experiment is to observe (1) The basic principles of Mendelian Genetics: dominance, segregation and independent assortment; (2) Sex linkage as an example of Mendelian extensions; (3) The condition under which independent assortment applies. We will conduct a project with Drosophila melanogaster , commonly known as fruit flies, the same model system used by Morgan who discovered sex linked genes. In this experiment, each group will be assigned an unknown dihybrid cross (P generation) that is already set up by the instructor. By examine the F1 and F2 generation, you will try to find out which cross has been set up and prepare a voicethread presentation to present your data and write a comprehensive lab report on this experiment. In addition, we will learn (1) the basic structure and the life cycle of fruit flies and the basic techniques of culturing flies and setting up crosses; (2) how to deduct inheritance patterns based on experimental results; (3) how to use statistical analysis such as a chi-square analysis to test the validity of our hypothesis. This project is conducted by student groups. The same group gets the same unknown cross but each student will receive an independent set of data. The group is expected to combine their data together, troubleshoot and prepare a group presentation collaboratively. However, each student is expected to write his own lab report independently. Part Two - Crosses and Chi-square tests Watch the online video tutorials “Explaining the Chi square test: Tutorial for exercise #4” and “Morgan’s experiment for the white gene: Tutorial for exercise #4” or refer to the Genetics textbook by Snustad and Simmons The three principles of Mendel’s laws of genetics are the law of dominance, the law of segregation and the law of independent assortment. The law of dominance states that in a heterozygous condition, one allele dominates over the other allele therefore the presence of one phenotype will conceal the other one. The law of segregation states that the two alleles of the same gene segregate during gamete formation. The law of independent assortment states that alleles of different genes assort independently of each other during gamete formation. 1

General Genetics Laboratory UHD Exercise #4 4.1 Drosophila nomenclature In Drosophila nomenclature, we give a gene the name based on the mutant phenotype. For instance, a gene is called white if the mutant phenotype causes the eye color to be white. The white mutant phenotype is recessive. Therefore, the wild type allele of the white gene is written as w + and the recessive allele is w . The homozygous w + /w + flies have wild type red eyes, the homozygous w/w flies have white eyes and the heterozygous w + /w flies have red eyes. Because white gene is located on the X chromosome, it is considered to be sex linked. Male flies can either be w + /⌐ or w/⌐ (where ⌐ stands for the Y chromosome). w + /⌐ flies will have dark red eyes whereas w/⌐ have white eyes (Table 5.1). Another example is ebony . A recessive allele eb causes a black body color. The wild type allele of the ebony gene is written as eb + . Because it is on the third chromosome, it is autosomal and not sex-linked. Therefore both males and females can have the wild type grayish brown body color ( eb + /eb + or eb + /eb ) or mutant black body color ( eb/eb ) (Table 4.1). The seven mutations in Table 4.1 affect seven genes located on different chromosomes and are assigned symbols based on their mutant phenotypes below. Among them, Bar is the only dominant mutation. Complete the table by following the examples. Table 4.1 A summary of the mutations and genes and their location in the genome. All mutant alleles except for Bar are recessive. Dominant mutations are denoted with capital letters and recessive mutations are in lower cases. Gene Chromosome Wild type allele Mutant allele Genotype of an individual with the wildtype phenotype Genotype of an individual with the mutant phenotype Bar X B+ B yellow X y white X w + w w + /w + w + /w w + /⌐ w/w w/⌐ ebony 3 e + e e + /e + e + /e e/e apterou s 2 sepia 3 vestigial 2 2

General Genetics Laboratory UHD 4.3 Dihybird crosses A fly genotype can then be written as the collection of all symbols. But for simplicity, we will only track two genes at a time. For instance, if we cross two mutant stocks white and vestigial in the P cross, there are two ways to do it. They are called reciprocal crosses . Reciprocal cross #1: a white male is crossed to a vestigial female. The two traits we are tracking are eye color and wing shape. According to table 1 in Unit 3 Part One file, a white male has white eyes and straight wings , therefore, its genotype is w/⌐;vg + /vg + . A vestigial female has dark red eyes and reduced wings , therefore, its genotype should be w + /w + ;vg/vg . The crossing scheme of the P generation should be w/⌐;vg + /vg + X w + /w + ;vg/vg Reciprocal cross #2: a white female is crossed to an vestigial male The two traits we are tracking are eye color and wing shape. According to table 1 in Unit 3 Part One file, a white female has __________ and __________ , therefore, its genotype is _______________. A vestigial male has ___________ and ___________ , therefore, its genotype should be ___________________ . The crossing scheme of the P generation should be ____________________________. For instance, if you cross a double mutant with a wildtype fly, there are also two ways too. Reciprocal cross #1: a white and vestigial male is crossed to a wildtype female The two traits we are tracking are eye color and wing shape. According to table 3.2, a white and vestigial male has white eyes and reduced wings , therefore, its genotype is w/⌐;vg/vg. A wildtype female has dark red eyes and straight wings , therefore, its genotype should be w + /w + ;vg + /vg + . The crossing scheme of the P generation should be w/⌐;vg/vg X w + /w + ;vg + /vg + Reciprocal cross #2: a white and vestigial female is crossed to a wildtype male The two traits we are tracking are eye color and wing shape. According to table 3.2, a white and vestigial female has __________ and __________ , therefore, its genotype is _______________. A wildtype male has ___________ and ___________ , therefore, its genotype should be ___________________ . The crossing scheme of the P generation should be ____________________________. 4

General Genetics Laboratory UHD Exercise 5: Predicting cross outcomes Watch the online video tutorial “Writing fly crosses: Tutorial for exercise #5. 5.1 Now we will practice writing crosses and predicting outcomes. The instructor will teach you how to write down the crossing scheme of a dihybrid cross and predict the phenotypic ratios in the F1 and F2 generations. Demo crosses: Practice cross: a white male is crossed with a vestigial female Reciprocal practice cross: a white female is crossed with a vestigial male Answer the following questions: If two genes do not assort independently, will the observed F2 generation be consistent with the predicted cross outcome? How can you tell whether the two genes assort independently or not? 5

General Genetics Laboratory UHD Chi-Square Table 7