PLEASE make sure to watch this video carefully and take notes. You need to know ALL of this, not just for this activity, but for the lesson tomorrow.

How to Create a Chromosome Map from Crossover Frequencies

Recombination: During crossing-over (prophase I of Meiosis), genes on chromosomes switch places. Crossover is random, but the likelihood that 2 genes crossover will increase if those genes are farther apart. Genes closer together are more likely to "stick together" and not switch places.

Gene Linkage Maps: Using the crossover frequencies, you can construct a map to represent the distances between genes.

This map shows chromosome #2 of Drosophila melanogaster. The distance between the genes can be written as a percentage or as a MAP UNIT. The gene for body color and and wing size are 17 map units apart.

Step 3: Subtraction will be necessary to determine the final distances between each gene.

Practice Problems