Genetics Laboratory Introduction

Drosophila melanogaster, common fruit fly - Relatively short generation time (10 days at 25 ⁰C) - Handling is easy due to small size - Small space requirement - Easy breeding in the laboratory - large number of offsprings

Larvea: feeding form Pupa : stationary form

Egg-larval period is about 5 days Life cycle is about 10 days at 25 ⁰C

Male vs. Female

To Mix Medium: Add one measure of powder and 5-10 yeasts into culture bottle. Add one and a half measure of water. Yeasts digest the food and prepare a rotten medium where Drosophila grow and lay eggs and larval development takes place. The medium should not be excessively watery to prevent flies death due to drowning.

Tranquilizing Flies- “Fly Nap” 1.Dip wand in “fly nap” and then let it stick halfway in vial (foam keeps it in place)‏ 2.Let sit for 3-5 minutes, or until flies are unconscious. 3.Flies are out for minutes. Take flies out and observe. 4.When putting unconscious flies back, sometimes it is best to put vial on its side. (Otherwise you risk unconscious flies sticking to medium). Flies can survive just fine in vial that is on its side. (Medium is sticky and does not move around)‏

Transmission Reports

Generations P Generation- You will initially get your P generation. You can assume your parent fruit flies are TRUE BREEDING. (What does this mean?) F 1 Generation- Breed the parents (cross you were assigned) and the offspring are the F1. You must count/record your F1s. F 2 Generation- Breed your F1’s. You must count/record your F2s AND do chi square statistical analysis of the F2 generation. You then turn these into your assistant.

Specific Write-up reminders: You must include your raw data. You need a null hypothesis (H o ) and an alternative hypothesis (H 1 ). You must evaluate most of your work using chi square statistical analysis on F2 generation.

The Hypothesis H o : There is no significant difference between the expected and observed results, following the phenotypic ratio of (enter your ratio here!). H 1 : There is a significant difference between the expected and observed results following the phenotypic ratio of (enter your ratio here!).

How to do a Chi Square Step 1 Indicate the type of cross you did. Give your H 0. Compare phenotypic ratio of expected and observed phenotypes Wild type and Ebony ( Caracter with non sex linked body color)‏

Step 2: Total each category (to get degrees of freedom)‏ Monohybrid (2 categories) for instance: -wild vs. ebony

Step 3 Apply the Chi-square statistic. X 2 = Σ O=observed number in a phenotypic category E=expected number in a phenotypic category X 2 = “chi-square” Σ = sigma “sum of” (O-E) 2 E

Why do we “fail to reject” instead of accept? A chi-square less than the critical value leads to the conclusion that the null hypothesis cannot be rejected, which is slightly different from being accepted. It may be that it cannot be rejected (proven false) due to small sample size, large variation in the data, etc. And in science, it’s easier to prove something false than it is to prove something true. Example: If someone says ‘I always tell the truth’, you only need to show one example of a lie to prove it false, but a thousand examples of telling the truth, while providing substantial evidence, cannot prove it true.