November 26, 2007. Janelle Eslinger. 3/3.

What went down in class today:

1. What are barr bodies?


2. Marked the test from Friday on Mandelian Genetics.


3. Gene mapping in the note handout. Complete the questions at the end of the handout and reffer to pages 450 & 503 in the textbook.


4. Corrections for the Mandelian Genetics test are due on Monday, December 3. You have the opportunity to gain 1/3 of the marks you missed!


5. We also have a Quiz on Chapter 21 & 22 on Thursday, November 29.

Important terms and a summary of the material covered:

Linked Genes - are located on the same chormisome. Genes located on the same chromosome tend ot be transmitted together.

This helps explain the difference that occured when Morgan was breeing fruit flies. Crossing over, (a term learned in meiosis chapter) provides new combinations.

For example, imagine a man who has one chromosome with brown-eye and brown-hair genes, and another chromosome with blue-eye and blonde-hair genes in his cells. Usually, his sperm cells will have either brown-eye and brown-hair genes, or blue-eye and blonde-hair genes. But if crossing over occurs, the man will produce one sperm cell with brown-eye and blonde-hair genes, and another with blue-eye and brown-hair genes.

The crossover frequency is another important term to consider. A crossover value of 1% indicates that the genes are close to each other. A crossover value of 12% indicates that the genes are much farther apart. The greather the crossover frequency of crossover, the greater the map distance. (Map Distance - refers to the distance between two genes along the same chromisome).

What are the maps like that are being made now?

The genome's cartographers are now making maps that combine features of both genetic-linkage and physical maps. As mapping techniques advance, scientists try to create maps with more landmarks that are more closely, evenly, and accurately spaced. But in contrast to DNA sequencing, which has become increasingly automated, genome mapping still can only be accomplished by experienced scientists.

This website was really helpful for understanding gene mapping. http://www.genomenewsnetwork.org/resources/whats_a_genome/Chp3_1.shtml#chp3#1