DOCSLIB.ORG

Measuring and Managing Genetic Variability in Small Populations Hubert De Rochambeau, Florence Fournet-Hanocq, Jacqueline Vu Tien Khang

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Measuring and Managing Genetic Variability in Small Populations Hubert De Rochambeau, Florence Fournet-Hanocq, Jacqueline Vu Tien Khang Measuring and managing genetic variability in small populations Hubert de Rochambeau, Florence Fournet-Hanocq, Jacqueline Vu Tien Khang To cite this version: Hubert de Rochambeau, Florence Fournet-Hanocq, Jacqueline Vu Tien Khang. Measuring and man- aging genetic variability in small populations. Annales de zootechnie, INRA/EDP Sciences, 2000, 49 (2), pp.77-93. 10.1051/animres:2000109. hal-00889883 HAL Id: hal-00889883 https://hal.archives-ouvertes.fr/hal-00889883 Submitted on 1 Jan 2000 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Ann. Zootech. 49 (2000) 77–93 77 © INRA, EDP Sciences Review article Measuring and managing genetic variability in small populations Hubert DE ROCHAMBEAU*, Florence FOURNET-HANOCQ, Jacqueline VU TIEN KHANG Station d’Amélioration Génétique des Animaux, BP 27, 31326 Auzeville Cedex, France (Received 2 July 1999; accepted 14 January 2000) Abstract — Genetic variability in small populations is affected by specific phenomena. The joint effects of genetic drift and selection, in addition to the decrease in genetic variance due to the mere selection (Bulmer effect), enhance the risk of losing alleles at selected or unselected genes and increase the inbreeding in the population by changing the family structure. Criteria for measuring this change in genetic variability are derived from the three approaches to describe the genetic variabil- ity. At the genealogical level, the kinship and inbreeding coefficients, or the effective population size, can be used. At the trait level, the estimation of its heritability is a good measure of remaining genetic variance. At the genome level, studying the polymorphism of known genetic markers can inform on the degree of genetic diversity. These criteria are to be integrated in specific tools for the management of the genetic variability. After a short introduction on the basic concepts needed for the study of genetic variability in small populations, the main criteria available to measure its change in populations is exposed and their relative efficiencies discussed. The strategies for monitoring genetic variability, deriving from the previous criteria, are illustrated through different examples. small population / genetic variability / genetic drift / genetic management / conservation programme Résumé — Mesure et gestion de la variabilité génétique dans les petites populations. Plusieurs phénomènes spécifiques modifient la variabilité génétique dans les petites populations. Les effets com- binés de la dérive génétique et de la sélection, auxquels s’ajoutent la réduction de la variance géné- tique due spécifiquement à la sélection (Effet Bulmer), renforcent le risque de perdre des allèles à des loci sélectionnés et non sélectionnés et augmentent la consanguinité de la population du fait de la modi- fication de la structure familiale. Les critères de mesure de la variabilité génétique dérivent des 3 approches utilisées pour la décrire. Les coefficients de consanguinité et de parenté ou l’effectif génétique résument l’information généalogique. L’estimation de l’héritabilité d’un caractère syn- thétise la variabilité génétique restante. L’étude du polymorphisme pour des marqueurs génétiques * Correspondence and reprints Tel.: 33 (0)5 61 28 51 88; fax: 33 (0)5 61 28 53 53; e-mail: [email protected] 78 H. de Rochambeau et al. décrit la variabilité existante au niveau du génome. Ces critères servent à construire des outils de ges- tion de la variabilité. Après une brève introduction qui présente les concepts utiles à l’étude de la varia- bilité génétique, les principaux critères utilisés pour suivre son évolution sont décrits, et leur effica- cité est comparée. Les stratégies de gestion qui dérivent de ces critères sont ensuite illustrées à partir de l’étude de quelques exemples. petites populations / variabilité génétique / dérive génétique / gestion génétique / programme de conservation 1. INTRODUCTION tions of genetic variability used to measure its evolution will be compared. A presen- Genetic variability may be defined as the tation of more or less complex rules for “genetic ability to vary”, and therefore the monitoring small populations will conclude capacity to respond to environmental vari- this paper. The concepts developed in the ations or changes in the selection objectives. first part will concern any kind of small pop- Genetic variability is also the basis of any ulation, but the last part of the paper will genetic progress, when a population is focus on populations under conservation undergoing selection. Its maintenance at a programmes. consistent level is then of great concern in any population, selected or not, and what- ever its size. However, the smaller the pop- 2. BASIC PHENOMENA ulation, the higher the need for conserva- AND CONCEPTS tion, as there are less individuals so less “containers” for genetic variability. 2.1. Genetic drift and inbreeding But how can we decide that a population is “small”? What may be called “small pop- A restricted number of individuals con- ulation” is a population where the number of tributing to the next generation in a small individuals really contributing to the next population will have two consequences: generation is restricted, whether the total genetic drift and inbreeding. population size is really small (up to sev- Genetic drift has been defined by Wright eral hundreds of individuals) or the use of [51] for a neutral, (i.e. non selected) bi-allelic techniques allowing a large diffusion of locus, as random fluctuations of allelic fre- progress (artificial insemination, multiple quencies around their initial value, due to ovulation and embryo transfer) reduces the the sampling of alleles from one generation number of reproducers in one sex or both, or to the next, finally leading to the fixation of provokes a disequilibrium in the reproduc- one of the alleles (and the loss of the other). ers’ contributions to subsequent generations. The higher the number of generations con- Some domestic populations may then be sidered and the smaller the population, the considered as “small populations” and be greater the fluctuations. This can be concerned by the following. extended to more than one locus, providing This paper aims to present the basic con- a progressive increase of homozygosity over cepts and the main tools for the manage- all the genes in the population, due to the ment of genetic variability in a small popu- successive samplings of alleles over time lation, with or without selection. After a and the consecutive random fixations of description of the phenomena acting on some alleles and losses of others. genetic variability in such a population, the The probabilistic approach of inbreed- criteria derived from the different defini- ing was derived by Malecot [29]. In small Genetic management of small populations 79 populations, the number of founder ances- – a dominance effect D, resulting from tors is restricted (“founder” means an indi- interactions between the paternal and mater- vidual whose parents are unknown). Over nal alleles at a given locus; successive generations, even if matings are – an epistatic effect I, concerning inter- panmictic, individuals are more likely to be actions between alleles at different loci. related, due to one or more common ances- In most cases, only the additive genetic tors, and thereafter, matings between rela- part of the performance is considered and tives produce inbred individuals. As a con- the genetic variability of a quantitative trait sequence, two homologous genes could be is approached by its additive genetic vari- “identical by descent”, i.e. they are both ance. Several models, either analytic [6, 49] deriving by copy from the same gene in a or stochastic [15], differing by the hypothe- common ancestor. ses they rely on, are available to describe and predict the evolution of additive genetic 2.2. Consequences on genetic variability variance over generations. The more com- plex the model, the more accurate the pre- Genetic drift and inbreeding were two diction of genetic variance over time. This is aspects of a phenomenon which increases illustrated in Figure 1, where the predictions the rate of homozygous genes in the popu- provided by three analytical models based lation. As the genetic variability of the trait on Gaussian theory are compared. Wright model [51] and Bulmer model [3] consider under study can be characterised by the only one effect at a time on genetic vari- number of different alleles available at the ance, either genetic drift (Wright model) or loci controlling the trait in the whole popu- selection (Bulmer model). The Verrier et al. lation, the loss of alleles due to genetic drift model [49] accounts for genetic drift, selec- or inbreeding consecutively decreases the tion and interactions between the two fac- genetic variability. tors. The Wright model highlights the effect The previous concepts were developed of genetic drift on genetic variance: the for one single neutral locus. Most of the remaining variance after 30 generations
Load more

Recommended publications
  • Adaptation from Standing Genetic Variation and from Mutation
    Adaptation from standing genetic variation and from mutation Experimental evolution of populations of Caenorhabditis elegans Sara Carvalho Dissertation presented to obtain the Ph.D degree in Biology Instituto de Tecnologia Química e Biológica | Universidade Nova de Lisboa Oeiras, Janeiro, 2012 Adaptation from standing genetic variation and from mutation Experimental evolution of populations of Caenorhabditis elegans Sara Carvalho Dissertation presented to obtain the Ph.D degree in Evolutionary Biology Instituto de Tecnologia Química e Biológica | Universidade Nova de Lisboa Research work coordinated by: Oeiras, Janeiro, 2012 To all the people I love. Table of contents List of Figures 3 List of Tables 5 Acknowledgements 7 Abstract 9 Resumo 13 CHAPTER 1 – Introduction 17 1.1 And yet…it changes 18 1.1.2 Evolution and adaptation 19 1.1.3 Mutation and standing genetic variation 25 Mutation 26 Standing genetic variation 32 Mutation versus standing genetic variation 34 Genetic recombination among adaptive alleles 35 1.1.4 Other players in evolution 37 1.1.5 Evolution in the wild and in the lab 40 1.1.6 Objectives 43 1.2 Caenorhabditis elegans as a model for experimental evolution 45 1.2.1 Experimental populations of C. elegans 50 1.3 References 53 CHAPTER 2 – Adaptation from high levels of standing genetic 63 variation under different mating systems 2.1 Summary 64 2.2 Introduction 64 2.3 Materials and Methods 69 2.4 Results 84 2.5 Discussion 98 2.6 Acknowledgements 103 2.7 References 103 2.8 Supplementary information 110 1 CHAPTER 3 – Evolution
    [Show full text]
  • Genetic Variation in Polyploid Forage Grass: Assessing the Molecular Genetic Variability in the Paspalum Genus Cidade Et Al
    Genetic variation in polyploid forage grass: Assessing the molecular genetic variability in the Paspalum genus Cidade et al. Cidade et al. BMC Genetics 2013, 14:50 http://www.biomedcentral.com/1471-2156/14/50 Cidade et al. BMC Genetics 2013, 14:50 http://www.biomedcentral.com/1471-2156/14/50 RESEARCH ARTICLE Open Access Genetic variation in polyploid forage grass: Assessing the molecular genetic variability in the Paspalum genus Fernanda W Cidade1, Bianca BZ Vigna2, Francisco HD de Souza2, José Francisco M Valls3, Miguel Dall’Agnol4, Maria I Zucchi5, Tatiana T de Souza-Chies6 and Anete P Souza1,7* Abstract Background: Paspalum (Poaceae) is an important genus of the tribe Paniceae, which includes several species of economic importance for foraging, turf and ornamental purposes, and has a complex taxonomical classification. Because of the widespread interest in several species of this genus, many accessions have been conserved in germplasm banks and distributed throughout various countries around the world, mainly for the purposes of cultivar development and cytogenetic studies. Correct identification of germplasms and quantification of their variability are necessary for the proper development of conservation and breeding programs. Evaluation of microsatellite markers in different species of Paspalum conserved in a germplasm bank allowed assessment of the genetic differences among them and assisted in their proper botanical classification. Results: Seventeen new polymorphic microsatellites were developed for Paspalum atratum Swallen and Paspalum notatum Flüggé, twelve of which were transferred to 35 Paspalum species and used to evaluate their variability. Variable degrees of polymorphism were observed within the species. Based on distance-based methods and a Bayesian clustering approach, the accessions were divided into three main species groups, two of which corresponded to the previously described Plicatula and Notata Paspalum groups.
    [Show full text]
  • Worldwide Genetic Variation in Dopamine and Serotonin Pathway
    American Journal of Medical Genetics Part B (Neuropsychiatric Genetics) 147B:1070–1075 (2008) Worldwide Genetic Variation in Dopamine and Serotonin Pathway Genes: Implications for Association Studies Michelle Gardner,1,2 Jaume Bertranpetit,1,2 and David Comas1,2* 1Unitat de Biologia Evolutiva, Universitat Pompeu Fabra, Doctor Aiguader, Barcelona, Spain 2CIBER Epidemiologı´a y Salud Pu´blica (CIBERESP), Barcelona, Spain The dopamine and serotonin systems are two of the most important neurotransmitter pathways in Please cite this article as follows: Gardner M, Bertran- the human nervous system and their roles in petit J, Comas D. 2008. Worldwide Genetic Variation controlling behavior and mental status are well in Dopamine and Serotonin Pathway Genes: Implica- accepted. Genes from both systems have been tions for Association Studies. Am J Med Genet widely implicated in psychiatric and behavioral Part B 147B:1070–1075. disorders, with numerous reports of associations and almost equally as numerous reports of the failure to replicate a previous finding of associa- tion. We investigate a set of 21 dopamine and serotonin genes commonly tested for association INTRODUCTION with psychiatric disease in a set of 39 worldwide The dopamine and serotonin systems are two of the major populations representing global genetic diversity neurotransmitter systems in humans. Dopamine affects brain to see whether the failure to replicate findings of processes that control both motor and emotional behavior and association may be explained by population based it is known to have a role in the brain’s reward mechanism differences in allele frequencies and linkage [Schultz, 2002]. Serotonin has a critical role in temperature disequilibrium (LD) in this gene set.
    [Show full text]
  • 1055.Full.Pdf
    Copyright 1999 by the Genetics Society of America Evolution of Genetic Variability and the Advantage of Sex and Recombination in Changing Environments Reinhard BuÈrger Institut fuÈr Mathematik, UniversitaÈt Wien, A-1090 Wien, Austria and International Institute of Applied Systems Analysis, A-2361 Laxenburg, Austria Manuscript received February 22, 1999 Accepted for publication May 12, 1999 ABSTRACT The role of recombination and sexual reproduction in enhancing adaptation and population persistence in temporally varying environments is investigated on the basis of a quantitative-genetic multilocus model. Populations are ®nite, subject to density-dependent regulation with a ®nite growth rate, diploid, and either asexual or randomly mating and sexual with or without recombination. A quantitative trait is determined by a ®nite number of loci at which mutation generates genetic variability. The trait is under stabilizing selection with an optimum that either changes at a constant rate in one direction, exhibits periodic cycling, or ¯uctuates randomly. It is shown by Monte Carlo simulations that if the directional- selection component prevails, then freely recombining populations gain a substantial evolutionary advan- tage over nonrecombining and asexual populations that goes far beyond that recognized in previous studies. The reason is that in such populations, the genetic variance can increase substantially and thus enhance the rate of adaptation. In nonrecombining and asexual populations, no or much less increase of variance occurs. It is explored by simulation and mathematical analysis when, why, and by how much genetic variance increases in response to environmental change. In particular, it is elucidated how this change in genetic variance depends on the reproductive system, the population size, and the selective regime, and what the consequences for population persistence are.
    [Show full text]
  • Review Questions Meiosis
    Review Questions Meiosis 1. Asexual reproduction versus sexual reproduction: which is better? Asexual reproduction is much more efficient than sexual reproduction in a number of ways. An organism doesn’t have to find a mate. An organism donates 100% of its’ genetic material to its offspring (with sex, only 50% end up in the offspring). All members of a population can produce offspring, not just females, enabling asexual organisms to out-reproduce sexual rivals. 2. So why is there sex? Why are there boys? If females can reproduce easier and more efficiently asexually, then why bother with males? Sex is good for evolution because it creates genetic variety. All organisms depend on mutations for genetic variation. Sex takes these preexisting traits (created by mutations) and shuffles them into new combinations (genetic recombination). For example, if we wanted a rice plant that was fast-growing but also had a high yield, we would have to wait a long time for a fast-growing rice to undergo a mutation that would also make it highly productive. An easy way to combine these two desirable traits is through sexually reproduction. By breeding a fast-growing variety with a high-yielding variety, we can create offspring with both traits. In an asexual organism, all the offspring are genetically identical to the parent (unless there was a mutation) and genetically identically to each other. Sexual reproduction creates offspring that are genetically different from the parents and genetically different from their siblings. In a stable environment, asexual reproduction may work just fine. However, most ecosystems are dynamic places.
    [Show full text]
  • Genetic Diversity of Marine Gastropods: Contrasting Strategies of Cerithium Rupestre and C
    MARINE ECOLOGY - PROGRESS SERIES Vol. 28: 99-103, 1986 Published January 9 Mar. Ecol. Prog. Ser. Genetic diversity of marine gastropods: contrasting strategies of Cerithium rupestre and C. scabridum in the Mediterranean Sea Batia Lavie & Eviatar Nevo Institute of Evolution, University of Haifa, Mount Carrnel, Haifa, Israel ABSTRACT: Allozymic variation encoded by 25 gene loci was compared and contrasted in natural co- existing populations of the marine gastropods Cerithiurn rupestre and C. scabridum collected along the rocky beach of the northern Mediterranean Sea of Israel. C. rupestre showed considerably less genic diversity than C. scabridurn. Results support the niche-width variation hypothesis as C. scabridum may be considered a species characterized by a broader ecological niche than C. rupestre. However, the extreme difference between the genic diversity of the 2 species might result from at least 2 sets of factors reinforcing each other, namely the ecological niche as well as the life zone and life history characteristics. INTRODUCTION (Van Valen 1965) there should be a positive correlation between the niche breadth and the level of genetic Since its first application for studies of genetic diver- diversity. Genetic-ecological correlations over many sity, the technique of electrophoresis has been used in species demonstrate inferentially the adaptive signifi- hundreds of surveys of natural populations. Nevo et al. cance of enzyme polymorphisms (see critical discus- (1984) analysed the genetic variability of 1111 species sion in Nevo et al. 1984 and references therein), belonging to 10 higher taxa. The distribution patterns although exceptions have been found (e.g. Somero & obtained for both genetic indices of diversity, hetero- Soule' 1974).
    [Show full text]
  • Contemporary and Historic Factors Influence Differently Genetic
    Heredity (2015) 115, 216–224 & 2015 Macmillan Publishers Limited All rights reserved 0018-067X/15 www.nature.com/hdy ORIGINAL ARTICLE Contemporary and historic factors influence differently genetic differentiation and diversity in a tropical palm C da Silva Carvalho1,2, MC Ribeiro2, MC Côrtes2, M Galetti2 and RG Collevatti1 Population genetics theory predicts loss in genetic variability because of drift and inbreeding in isolated plant populations; however, it has been argued that long-distance pollination and seed dispersal may be able to maintain gene flow, even in highly fragmented landscapes. We tested how historical effective population size, historical migration and contemporary landscape structure, such as forest cover, patch isolation and matrix resistance, affect genetic variability and differentiation of seedlings in a tropical palm (Euterpe edulis) in a human-modified rainforest. We sampled 16 sites within five landscapes in the Brazilian Atlantic forest and assessed genetic variability and differentiation using eight microsatellite loci. Using a model selection approach, none of the covariates explained the variation observed in inbreeding coefficients among populations. The variation in genetic diversity among sites was best explained by historical effective population size. Allelic richness was best explained by historical effective population size and matrix resistance, whereas genetic differentiation was explained by matrix resistance. Coalescence analysis revealed high historical migration between sites within landscapes and constant historical population sizes, showing that the genetic differentiation is most likely due to recent changes caused by habitat loss and fragmentation. Overall, recent landscape changes have a greater influence on among-population genetic variation than historical gene flow process. As immediate restoration actions in landscapes with low forest amount, the development of more permeable matrices to allow the movement of pollinators and seed dispersers may be an effective strategy to maintain microevolutionary processes.
    [Show full text]
  • Genetic Variation in Subdivided Populations and Conservation Genetics
    Heredity 57 (1986) 189—198 The Genetical Society of Great Britain Received 19 November 1985 Geneticvariation in subdivided populations and conservation genetics Sirkka-Liisa Varvio*, University of Texas Health Science Center at Ranajit Chakraborty and Masatoshi Nei Houston, Center for Demographic and Population Genetics, P.O. Box 20334, Houston, Texas 77225 The genetic differentiation of populations is usually studied by using the equilibrium theory of Wright's infinite island model. In practice, however, populations are not always in equilibrium, and the number of subpopulations is often very small. To get some insight into the dynamics of genetic differentiation of these populations, numerical computations are conducted about the expected gene diversities within and between subpopulations by using the finite island model. It is shown that the equilibrium values of gene diversities (H and H) and the coefficient of genetic differentiation (G) depend on the pattern of population subdivision as well as on migration and that the GST value is always smaller than that for the infinite island model. When the number of migrants per subpopulation per generation is greater than 1, the equilibrium values of H and HT are close to those for panmictic populations, as noted by previous authors. However, the values of H, HT, and GST in transient populations depend on the pattern of population subdivision, and it may take a long time for them to reach the 95 per cent range of the equilibrium values. The implications of the results obtained for the conservation of genetic variability in small populations are discussed. It is argued that any single principle should not be imposed as a general guideline for the management of small populations.
    [Show full text]
  • Adaptation from Standing Genetic Variation to a Moving Phenotypic Optimum
    HIGHLIGHTED ARTICLE GENETICS | INVESTIGATION Catch Me if You Can: Adaptation from Standing Genetic Variation to a Moving Phenotypic Optimum Sebastian Matuszewski,*,1 Joachim Hermisson,*,† and Michael Kopp‡ *Mathematics and BioSciences Group, Faculty of Mathematics, University of Vienna, A-1090 Vienna, Austria, †Max F. Perutz Laboratories, A-1030 Vienna, Austria, and ‡Aix Marseille Université, Centre National de la Recherche Scientifique, Centrale Marseille, I2M, Unité Mixte de Recherche 7373, 13453 Marseille, France ABSTRACT Adaptation lies at the heart of Darwinian evolution. Accordingly, numerous studies have tried to provide a formal framework for the description of the adaptive process. Of these, two complementary modeling approaches have emerged: While so- called adaptive-walk models consider adaptation from the successive fixation of de novo mutations only, quantitative genetic models assume that adaptation proceeds exclusively from preexisting standing genetic variation. The latter approach, however, has focused on short-term evolution of population means and variances rather than on the statistical properties of adaptive substitutions. Our aim is to combine these two approaches by describing the ecological and genetic factors that determine the genetic basis of adaptation from standing genetic variation in terms of the effect-size distribution of individual alleles. Specifically, we consider the evolution of a quantitative trait to a gradually changing environment. By means of analytical approximations, we derive the distribution
    [Show full text]
  • A Glossary of Terms for Restoration Genetics
    Paul R. Salon Allele – The specific composition of DNA at each gene is known as an allele. Multiple alleles of a gene maybe A Glossary of Terms for Restoration Genetics USDA-NRCS Syracuse, NY generated by mutations which are structural or chemical changes in DNA at a specific location on a chromosome (locus), this generates genetic variation. Genetic shift – A change in the germplasm balance of a cross pollinated variety, usually caused by Biodiversity - The total variability within and among species of living organisms and the ecological complexes environmental selection pressures, or nursery practices and selection. that they inhabit. Biodiversity has three levels - ecosystem, species, and genetic diversity reflected in the Genetic vulnerability - Having a narrow range of genetic diversity and reacting uniformly to diverse external number of different species, the different combination of species, and the different combinations of genes within conditions. (Applied to breeding populations of varieties or species). each species. Genotype - The genetic constitution of an individual or group of plants. It is the set of alleles it possesses at a Biotype - A group of individuals within a population occurring in nature, all with essentially the same genetic certain locus or over particular or all loci. constitution. A species usually consists of many biotypes. See also “ecotype”. Germplasm – Genetic material that determines the morphological and physiological characteristics of a species. Chromosomes - Are thread like DNA and protein-based structures in cells whose function is the orderly duplication and distribution of genes during cell division. Heterozygote – If alleles at a locus are different. Cultivar - The international term cultivar denotes an assemblage of cultivated plants that is clearly distinguished Homozygote – If alleles at a locus are the same, the locus is homozygous and the organism is a homozygote for that by any characters (morphological, physiological, cytological, chemical, or others) and when reproduced (sexually gene or trait.
    [Show full text]
  • Chapter 23: Population Genetics (Microevolution)  Microevolution Is a Change in Allele Frequencies Or Genotype Frequencies in a Population Over Time
    Chapter 23: Population Genetics (Microevolution) Microevolution is a change in allele frequencies or genotype frequencies in a population over time Genetic equilibrium in populations: the Hardy-Weinberg theorem Microevolution is deviation from Hardy- Weinberg equilibrium Genetic variation must exist for natural selection to occur . • Explain what terms in the Hardy- Weinberg equation give: – allele frequencies (dominant allele, recessive allele, etc.) – each genotype frequency (homozygous dominant, heterozygous, etc.) – each phenotype frequency . Chapter 23: Population Genetics (Microevolution) Microevolution is a change in allele frequencies or genotype frequencies in a population over time Genetic equilibrium in populations: the Hardy-Weinberg theorem Microevolution is deviation from Hardy- Weinberg equilibrium Genetic variation must exist for natural selection to occur . Microevolution is a change in allele frequencies or genotype frequencies in a population over time population – a localized group of individuals capable of interbreeding and producing fertile offspring, and that are more or less isolated from other such groups gene pool – all alleles present in a population at a given time phenotype frequency – proportion of a population with a given phenotype genotype frequency – proportion of a population with a given genotype allele frequency – proportion of a specific allele in a population . Microevolution is a change in allele frequencies or genotype frequencies in a population over time allele frequency – proportion of a specific allele in a population diploid individuals have two alleles for each gene if you know genotype frequencies, it is easy to calculate allele frequencies example: population (1000) = genotypes AA (490) + Aa (420) + aa (90) allele number (2000) = A (490x2 + 420) + a (420 + 90x2) = A (1400) + a (600) freq[A] = 1400/2000 = 0.70 freq[a] = 600/2000 = 0.30 note that the sum of all allele frequencies is 1.0 (sum rule of probability) .
    [Show full text]
  • Genetic Variability in Quantitative Characters Induced by Thermal Neutron Treatment of Diploid, Tetraploid and Hexaploid Oat
    Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1964 Genetic variability in quantitative characters induced by thermal neutron treatment of diploid, tetraploid and hexaploid oat seeds Carlos Luis Gonzalez Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Agriculture Commons Recommended Citation Gonzalez, Carlos Luis, "Genetic variability in quantitative characters induced by thermal neutron treatment of diploid, tetraploid and hexaploid oat seeds " (1964). Retrospective Theses and Dissertations. 2665. https://lib.dr.iastate.edu/rtd/2665 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. This dissertation has been 64—10,643 microfilmed exactly as received GONZALEZ, Carlos Luis, 1923- GENETIC VARIABILITY IN QUANTITATIVE CHARr- ACTERS INDUCED BY THERMAL NEUTRON TREATMENT OF DIPLOID, TETRAPLOID AND HEXAPLOID OAT SEEDS. Iowa State University of Science and Technology Ph.D., 1964 Agriculture, general University Microfilms, Inc., Ann Arbor, Michigan GENETIC VARIABILITY IN QUANTITATIVE CHARACTERS INDUCED BY THERMAL NEUTRON TREATMENT OF DIPLOID, TETRAPLOID AND HEXAPLOID OAT SEEDS by Carlos Luis Gonzalez A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of The Requirements for the Degree of DOCTOR OF PHILOSOPHY Major Subject: Crop Breeding Approved: Signature was redacted for privacy. In Cha/fga of Maj o Signature was redacted for privacy. Head of Major Department Signature was redacted for privacy.
    [Show full text]