Modern Heredity Part 1 Concept Review
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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
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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
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2. The following chart shows the crossover frequencies for genes on an autosome of the Armor Plated Squirtlesaur. Construct a chromosome map
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3. Construct a map given the following data.
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