The Theoretical Distribution of Lengths of Intact Chromosome Segments Around a Locus Held Heterozygous With Backcrossing in a Diploid Species

When two different isogenic lines of a diploid species (or two different species) are crossed, the resulting F1 individuals should be heterozygous at all the loci fixed for different alleles in the two strains (in the limit, at all the loci of the genome). If one of these loci is then held heterozyg...

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Bibliographic Details
Published in:Genetics (Austin) 1992-01, Vol.130 (1), p.205-209
Main Authors: Naveira, H, Barbadilla, A
Format: Article
Language:English
Subjects:
Alleles
Biological and medical sciences
Chromosomes
Classical genetics, quantitative genetics, hybrids
Crosses, Genetic
Fundamental and applied biological sciences. Psychology
Genetics
Genetics of eukaryotes. Biological and molecular evolution
Heterozygote
Investigations
Mathematics
Methods, theories and miscellaneous
Models, Genetic
Recombination, Genetic
Species Specificity
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Summary:When two different isogenic lines of a diploid species (or two different species) are crossed, the resulting F1 individuals should be heterozygous at all the loci fixed for different alleles in the two strains (in the limit, at all the loci of the genome). If one of these loci is then held heterozygous for several generations of repeated backcrossing to the same strain, the average length of intact chromosome segments (with reference to the original parental chromosome) on both sides of the selected locus, or, equivalently, the average length of segments surrounding that locus which are still heterozygous (with reference to the fully heterozygous F1 chromosome), may diminish, but cannot increase. Several authors have derived equations to predict this average. We show that the most widely used criterion, developed by R.A. Fisher, leads to serious overestimations of the true parametric values, when applied to early generation analyses, with the corresponding errors in the interpretation of experimental results. We then derive the exact equations both for the average and standard deviation of the lengths of intact chromosome segments surrounding a locus held heterozygous after any number of generations of backcrossing. Our results are in close agreement with those found by a former author, although involving a rather different approach.
ISSN:0016-6731
1943-2631
1943-2631
DOI:10.1093/genetics/130.1.205