Study Questions for
Topic 3: Genetic Linkage and Genetic
Mapping
Reading Assignment: Chapter 5 Sections 5.1 through 5.6 and Chapter 6, Section 6.8
Study guide for the Matching section of test 3:
The assigned reading, my Key Term List, all the study questions below
Study guide for the short answer/problem solving section of test 5: Questions to help you study for the problem solving test section: (G = Guide to Solving)
Linkage and Recombination of Genes in a Chromosome: 5.2; 5.6
- Calculation of recombination
frequency from crossover frequency Ch 5 G1; 5.3; 5.8; 5.11
- Predict gamete/progeny types/frequencies from recombination frequencies: 5.1; 5.4; 5.14; 5.20; 5.29; CP3
Genetic Mapping:
- Recombination and genetic distance: 5.9
- Calculate map distance from results of two-factor crosses: 5.17
Genetic Mapping in a Three-Point Testcross:
- Determining the map using data from a cross: Ch 5 G2; 5.18; 5.19
- Calculating progeny type/frequencies using data from a map or recombination frequencies: 5.12; 5.15; 5.27
Mapping by Tetrad Analysis
Linkage analysis in a Neurospora cross: 5.5; 5.25
Linkage analysis in a budding yeast cross: 5.7
Genetic Mapping in Human Pedigrees:
- Estimating map distance:
5.13; 5.26
- Calculating probabilities based on recombination frequencies Ch 5 G3
Molecular Mechanisms of Recombination
Gene Conversion: Ch 6 CP2 and CP3
Structure of a
a) Be able to draw the Holiday and Double-Strand Break and Repair models for recombination and show how regions of heteroduplex form.
b) Describe how DNA repair of the heteroduplex can cause gene conversion.
c) Illustrate how a holiday junction can be resolved to produce either recombinant or non-recombinant progeny.
Principles and Key Concepts
1. Genetic loci that do not assort independently during meiosis are said to be genetically linked.
2. Genetically linked loci are also physically linked. In other words, they are located on the same chromosome: they are syntenic.
3. Genetic linkage is typically not absolute because of crossing over (recombination) between syntenic loci during prophase I of meiosis.
4. The likelihood that a crossover will happen between two syntenic genes in a meiotic cell correlates with the physical distance between the genes.
5. The frequency of cross-overs between syntenic genes is used to calculate genetic distance in centiMorgans (cM), where .01 = 1 cM.
6. The relationship between genetic distance and physical distance is not linear because the frequency of crossing over is not uniform along a chromosome.
7. A cross-over event at one location can prevent additional cross-overs from occurring nearby, a phenomenon called chromosome interference.
8. Genetic mapping functions are equations (often represented as graphs) that describe how interference affects the relationship between recombination frequency and genetic map distance.
9. Crossing-over between syntenic genes results in formation of recombinant progeny, therefore, the percentage of recombinant progeny is used to estimate genetic distance.
10. The maximum percentage of recombinant progeny observable for syntenic genes in one cross is 0.50. This is the same as the percentage of recombinant progeny for genes on different chromosomes. Thus, a recombination frequency of 0.50 indicates independent assortment.
11. Saccharomyces cerevisiae (a yeast) and Neurospora crassa (a mold) are haploid fungi that are useful for studying genetic linkage and the mechanism of recombination.
12. Haploid fungal cells reproduce sexually by mating, where they fuse to produce a diploid cell (zygote), which then undergoes meiosis to produce four haploid progeny.
13. The haploid cells from each meiosis are found together in a sac (an ascus), allowing the direct analysis of all four products of a single meiosis.
14. Analysis of all four products of a single meiosis is a powerful analytical tool because
a) fewer progeny are needed to obtain good genetic linkage data
b) centromeres can be easily mapped
c) gene conversion can be detected, which reveals information about the mechanism of recombination
15. The current model for the mechanism of recombination is the Double-strand Break and Repair Model.