8: Gene Mapping and Recombination — Read

From LibreTexts, under not declared, as the source states it; its equations are written in TeX, which the PDF shows typeset. This page at LibreTexts.

8.1: Linkage
Genes close together on the same chromosome tend to be inherited together. Linkage explains departures from independent assortment and makes it possible to map genes.
8.2: Recombination
Recombination produces new combinations of alleles through independent assortment or crossing over. Distinguishing parental from recombinant gametes explains how to calculate recombination frequency and interpret the 50% expectation for unlinked loci.
8.3: Linkage Reduces Recombination Frequency
Complete linkage preserves parental allele combinations because no crossing over is detected between the loci. The resulting absence of recombinant gametes explains a recombination frequency of zero.
8.4: Crossovers Allow Recombination of Linked Loci
Crossing over between nonsister chromatids can separate alleles at linked loci. Chromosome diagrams explain partial linkage and why a recombination frequency of 50% does not necessarily mean that genes occupy different chromosomes.
8.5: Inferring Recombination From Genetic Data
Parental genotypes and testcross offspring reveal which allele combinations are parental or recombinant. Classifying these combinations identifies coupling or repulsion and determines which offspring to count when calculating recombination frequency.
8.6: Genetic Mapping
Recombination frequencies estimate genetic distances in centimorgans. Combining pairwise distances builds a map, while undetected double crossovers explain why recombination frequency can underestimate map distance.
8.7: Mapping With Three-Point Crosses
Three-point testcrosses use parental and double-crossover classes to identify the middle gene. Assigning offspring to crossover classes shows how to calculate each interval and include double crossovers in map distances.
8.8: Linkage and Mapping (Exercises)
Problems practice identifying recombinant offspring, designing mapping crosses, and calculating recombination frequencies. Two-point and three-point datasets test gene order, map distances, and corrections for double crossovers; answers support checking the reasoning.
8.9: Linkage and Mapping (Summary)
A review of linkage, recombination, and the use of testcrosses to construct genetic maps. Key distinctions connect chromosome position with recombination frequency and explain the limits of distance estimates.

8: Gene Mapping and Recombination is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

Contents

Text