Heterozygosity

by

Fred W. Allendorf

• LAST REVIEWED: 13 January 2014
• LAST MODIFIED: 13 January 2014
• DOI: 10.1093/obo/9780199941728-0039

Introduction

Heterozygosity—the condition of having two different alleles at a locus—is fundamental to the study of genetic variation in populations. Indeed, Mendel’s original work was based on tracing the transmission to progeny of the two alleles present in heterozygous individuals at individual loci or combinations of loci. Seminal theoretical work by Sewall Wright, beginning in the 1920s, developed our understanding of the roles of mutation, natural selection, genetic drift, and migration in maintaining heterozygosity in populations (see Maintenance of Heterozygosity). Early empirical population geneticists struggled to detect and measure heterozygosity in natural populations. The development of biochemical methods, beginning in the 1960s, allowed population geneticists to detect heterozygosity in all organisms, by using molecular methods, because the fundamental molecular biology of life is shared by all organisms, from bacteria to elephants. The role of natural selection versus genetic drift of neutral mutations in maintaining the unexpectedly high amount of heterozygosity found in natural populations became extremely controversial (see King and Jukes 1969, cited under Mutation and Genetic Drift). Many articles quickly appeared that demonstrated correlations between multiple-locus heterozygosity and phenotypes thought to be associated with fitness. The mechanisms underlying such associations are still largely unknown and are somewhat controversial today. The development of genomic techniques based on next-generation sequencing platforms, which provides the ability to screen tens to hundreds of thousands of loci throughout the genome for heterozygosity, has again revolutionized our understanding of heterozygosity in natural populations. The development of high-density genetic linkage maps permits genome-wide heterozygosity to be visualized as continuous distributions along the chromosomes at the scale of an entire genome. This procedure provides the ability to search the genome for genomic regions with exceptionally low or high heterozygosity, which indicates the action of natural selection. Similarly, detecting continuous regions of the genome that are characterized by the absence of heterozygosity (runs of homozygosity) provides the potential to detect and understand the effects of inbreeding in natural populations, which has not been previously possible. These approaches provide the potential to resolve some of the longest-standing controversies (e.g., the genetic basis of inbreeding depression) in population genetics that have been ongoing for more than one hundred years.

Journals

A variety of journals in the fields of genetics, evolution, ecology, and conservation publish papers that deal with the topic of heterozygosity. The journals of the leading scientific societies devoted to genetics regularly feature articles on heterozygosity: Genetics, Journal of Heredity, and Heredity. In addition, the journals Evolution, Genetics Research, and Proceedings of the Royal Society of London B: Biological Sciences have featured many articles on heterozygosity. In more-recent years, the journals Molecular Ecology and Conservation Genetics have included a number of papers on heterozygosity and its effects.

• Conservation Genetics.

  Conservation Genetics focuses on the conservation of genetic diversity and the application of genetic methods toward resolving problems in conservation. A sister journal, Conservation Genetics Resources, provides rapid publication of technical papers on methodological innovations or improvements, computer programs, and genomic resources.

• Evolution.

  The journal of the Society for the Study of Evolution has long been the leading journal in the field of evolution.

• Genetics.

  The primary journal of the Genetics Society of America has been published since 1916. For many years, the last few articles in every issue have been devoted to population and evolutionary genetics. A powerful search feature is provided online, which provides an excellent tool for doing historical research on genetic topics dating back nearly 100 years.

• Genetics Research.

  First published as Genetical Research in 1960, this journal changed its name in 2008. Genetics Research publishes original research on all aspects of human and animal genetics, with an emphasis on evolutionary and population genetics.

• Heredity.

  The official journal of the Genetics Society of the United Kingdom has been published since 1947. This journal covers a broad range of topics, with a focus on population and evolutionary genetics.

• Journal of Heredity.

  Published by the American Genetic Association since 1905. Featured topics include organismal genetics, conservation genetics, population structure, and molecular evolution.

• Molecular Ecology.

  Molecular Ecology was first published in 1992 as a source for the increasing number of papers using molecular genetic techniques to understand ecology and population biology. A sister journal, Molecular Ecology Research, publishes papers on molecular marker development, molecular diagnostics, barcoding, and DNA taxonomy.

• Proceedings of the Royal Society of London B: Biological Sciences.

  Proceedings of the Royal Society B has been published since 1800 and is currently committed to the rapid publication of high-quality, shorter papers. Most papers focus on organismal biology, with a strong focus on evolutionary biology and genetics.