Daily Newsletter March 14, 2012

Daily Newsletter March 14, 2012

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Daily Topic: Independent Assortment

Yesterday we talked about inheritance of one trait. Today we look at two different traits that are held on different chromosomes.


Mendel was again lucky. The traits that he looked at were found on different chromosomes (DNA molecules). The math would have been horrible if they had been on the same chromosome! Luckily, Mendel did not seem to have to worry about that.


With the Law of Segregation, Mendel showed that for each individual trait, a pea plant (and by extension a human) has two possible allele that they can carry for a single trait (gene). When ovum and sperm (pollen) are produced, the parent donates only one allele to the ovum or sperm; the parent donates only one allele to the next generation. Therefore a new individual is composed of a set of genes (and alleles) from the mother, and another set from the father.


So, what happens when you look at two different traits (genes)? Ultimately, what Mendel discovered is that the two different traits do no interfere with each other. An allele from the first gene is donated independently, and uninfluenced by, the allele from the second gene. So, you have a 50/50 chance of donating a given allele from the first gene, and a 50/50 chance of donating an allele from the second plant.

The math get's a little harder, but the idea is the same. The easiest way of showing what happens is to look at the Punnet Square for a visual interpretation of the probabilities. Below is a great picture of a Punnet square:

As you can see, on the top we put the Male Genetic Donation, and on the left side we put the Female Genetic Donation.  There is a 50/50 chance the male will donate a given allele, same with the female.  Look at how this is represented.  Male donation is either B or b.  Each has its own column.  For the female, each possible donation has its own row.  You then just cross-reference column and row to find out the possible offspring.  The Punnet square also provides a rapid visual.  4 possible offspring, 3 of which are purple.

The Punnet square can be expanded to look at a dihybrid cross (two traits).  Below is a good image of a dihybrid Punnet square, with the offspring ratios included:

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Daily Challenge:
Explain the concept of Independent Assortment. I made a point that this does not always occur when genes are on the same chromosome. So, what happens to Independent Assortment when genes (traits) are on the same chromosome? Why is it important?

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Administrative Note: Paper
There is confusion regarding the Due Date. I have said tonight, but I have included in the system a "Late" period which will last until Thursday Night. You will not be penalized if you get the paper in during the "Late" period.