- Mendelian Genetics
A gene is a unit of heredity on a chromosome and can have alternate forms called alleles. In sexually reproducing organisms each parent contributes one allele to their offspring that may or may not be like the other parent's allele. Alleles for a particular gene occur in pairs.

Alleles that mask expression of other alleles of a particular gene, but are themselves expressed are dominant, and are usually designated by a capital letter (for example, "B"). Alleles whose expression is masked by dominant alleles are recessive, and are designated by a lower case letter (for example, "b").

The genotype of an organism includes all the alleles present in the cell, whether they are dominant or recessive. The Biochemical manifestation of the trait is called the phenotype.

Monohybrid Cross of Corn - A monohybrid cross begins with experimental breeding between two parents that breed true for different forms of a single trait. The trait you will investigate in this problem is kernel color. The two forms of kernel color we will look at are Blue and Yellow. Corn is a good organism for this type of analysis since each grain (kernel) represents an independent offspring.

We start with a plant homozygous for blue kernels and cross it with a plant homozygous for yellow kernels. The offspring that result from this cross are called hybrids and are the F1 generation. When two individuals from the F1 generation are crossed the offspring is called the F2 generation. By observing the progeny from our crosses, we can form a couple of hypotheses.

• Kernel color is controlled by a single pair of alleles
• .The gene for Blue kernels is dominant.

One important fact to remember: Despite what you may think, most traits are not determined by single pairs of alleles. We can examine whether kernel color is truly a "single gene trait" by statistically comparing the results of our crosses with those that would be expected from a trait controlled by a single pair of alleles. One method to perform this type of analysis is called Chi square analysis (Χ²).

The formula for Chi square analysis is shown below. Don't let this simple math confuse you just because there are symbols in an equation. We will practice this once before you go to lab.

	Χ2 (chi squared) - This is just the name of the analysis.
	Σ- This is an operator that says to sum all the values to the right.
	o - These are values you measure or observe.
	e - These are values you expect. In chi square analysis you test o vs e.

Now lets gather some data to use in our chi square analysis. If the 'ear of corn" doesn't seem to work, you need the newest version of Flash; Get it here.