Drosophila: Statistical Significance and Chi Square

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Drosophila Lab

I. Introduction

Drosophila is a model organism for genetics experiments because it reproduces quickly and when it reproduces it reproduces in large quantities. Also it is a model organism because so much is already known about it. The Drosophila egg is about half a millimeter long. One day after fertilization the embryo develops and hatches worm like larvae. The larva continuously eats and grows, and moults four times. The fourth time it moults it forms an immobile pupa and turns into the winged form. It hatches in about 4 days and is fertile in 12 hours.

Statistical analysis can be used to determine if there is a significant difference between two of group data sets. One way to do this is to use a Chi square. The Chi square test produces a number which you compare to a statistical Chi square number. Each of these statistical numbers has a significance level. Significance levels show you how likely a result is due to chance. The most common level, which is also used in this lab, is .95 which makes something good enough to be believed. This means that 95% of the time the findings will be true, and 5% of the time they will not. If the Chi square produces a number which is less then the statistical value, you accept your null hypothesis, meaning that there is no significant difference between the data. If the Chi square test produces a number higher than the statistical value then you must refute your null hypothesis, meaning that there is a significant difference in your data. The null hypothesis used is that the pattern for inheritance is autosomal. The expected phenotype ratios for mutant to wild type flies were 1:4. The expected genotype ratios were 1:4 homozygous dominant (ant+/ant+), 2:4 heterozygous (ant+/ant), and 1:4 homozygous recessive (ant/ant). The null hypothesis is that there is no significant difference between this expected data and the data we collected.
II. Results

Male WTFemale WT Male Mutant Female mutant...
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