Genetics of Organisms (Lab 7)
| Other Links for this Lab Activity |
| Complete M and M's Chi
square activity Link to the AP Biology Genetics of Drosophila Lab Link to selected pictures of Drosophila Link to AP Biology Corn Genetics Lab Link to the Genetics
Lab Activity Results Lab 7 Review PowerPoint (modified from pdf file posted by Glen Cochrane at Half Hollows High School) |
Some Key Review Concepts
Mendelian Genetics
In the nineteenth century Gregor Mendel discovered the principles of inheritance through a series of careful experiments with peas. We know now that physical characteristics are transmitted from generation to generation according to some general patterns. When we have sufficient information about the parents, we can predict the occurrence of traits in offspring. And by analyzing the offspring, we can discern the mode of transmission – monohybrid or dihybrid, sex linked or autosomal.
Distinguishing Sex's
Adult Female: long pointy abdomen with stripes
Adult Male: blunt, darker abdomen
Lab Design
By breeding fruit flies (Drosophila melanogaster) of unknown genetic composition and studying the traits and ratios seen in their offspring, you will determine whether a trait follows a monohybrid or dihybrid pattern of inheritance and whether it is sex-linked or autosomal. You will use statistical analysis to support your conclusions.
Over a period of four weeks you will study three generations of flies. You begin with a parental (P) generation that has already mated. Check every generation for the following characteristics and record the numbers.
Males vs. Females
Ebony Body vs. Wingless
White Eyes vs. Sepia
Eyes
Note: When eggs and larvae appear, remove the adult flies from the vial so that you don't get generations mixed up.
Analysis of Results
The chi-square (
) test. This analytical tool tests the validity of a null
hypothesis, which states that there is no statistically significant
difference between the observed results of your experiment and the
expected results. When there is little difference between the observed
results and the expected results, you obtain a very low chi-square value;
your hypothesis is supported.
The formula for chi-square is:
= the sum of
where:
o = observed number of individuals
e =
expected number of individuals
In order to interpret the results of the chi-square computation, one must
use
a table of chi-square values. The degrees of freedom of
the results of a cross is equal to the phenotypic categories -1 (df=n-1).
Values greater than a 0.05 chance of probability are considered to be
possible due to random chance alone.
Link to a Chi-square table