Modern Heredity Part 1 Concept Review
by John Lundy
| 4 Questions
Note from the author:
An assignment to Insure understanding of how chromosome maps are created

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 1: Start with the genes that are the farthest apart first: B and C are 45 map units apart and would be placed far apart.
B ----------------------------------------- 45% ------------------------------------------C
Step 2: Solve it like a puzzle, using a pencil to determine the positions of the other genes.
Step 3: Subtraction will be necessary to determine the final distances between each gene.
Practice Problems
1. In Drosophila, bar shaped eyes (B), scalloped wings (S), Crossveinless wings (W), and Eye Color (C) are located on the X chromosome. The recombination frequency of each gene is indicated on the table. Construct a chromosome map. Paste your diagram Below
2. The following chart shows the crossover frequencies for genes on an autosome of the Armor Plated Squirtlesaur. Construct a chromosome map
3. Construct a map given the following data.
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