POPULATION ECOLOGY
Population Genetics - Research Connections
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Research Connection 1: Calculating genotype frequencies and testing for Hardy-Weinberg Equilibrium in domestic cats. |
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Research Connection 2: Artificial sexual selection and Hardy-Weinberg equilibrium in domestic dog breeding. |
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Research Connection 3: Natural selection and genetic drift in a granary mouse population. |
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Research Connection 4: Gene flow, genetic drift and geographic isolation in alpine butterflies. |
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Research Connection 5: Natural selection and mutation in the evolution of drug resistance in a pathogenic yeast. |
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1. INTRODUCTION TO POPULATION GENETICS Print Version
Population genetics is the science that studies genetic variation within and between populations. Specifically, population geneticists examine the frequency of different alleles in a population, whether this frequency changes over time, and the processes responsible for such change.
Alleles are different versions of the same gene. For example, one allele of the gene that controls for human eye colour encodes for brown eyes, whereas another allele encodes for blue eyes. Each individual within a population has its own unique combination of alleles. These alleles are the source of genetic variability within a population. Collectively, all the alleles in a population at a given time make up the gene pool.
Population geneticists can determine the genetic variation within a population by examining the phenotype (physical appearances) of individuals. In some cases the phenotype will be controlled by a dominant allele, wherein one allele of a gene masks the expression of the alternate allele. For example, if gene A determining fur length in cats has two alleles A1 (short fur) and A2 (long fur), wherein A1 shows complete dominance and A2 is recessive, then the combinations A1/A1 and A1/A2 will be expressed as short fur and A2/A2 will be expressed as long fur.
In other cases, phenotypic traits are expressed through alleles that display incomplete dominance. For example, if gene B determining amount of white fur in cats, wherein two alleles B1 (amount of white fur) and B2 show incomplete dominance, we find that the B1/B1 combination is expressed as more than 50% white fur, B1/B2 less than 50% white fur, and B2/B2 no white fur.
Increasingly population geneticists use molecular biology techniques to examine the genotype (an individual's DNA) to determine allele frequency. DNA from different parts of the cell may be used. Chromosomal DNA includes genes located on the chromosomes in the nucleus of a cell. Mitochondrial DNA (mtDNA) is DNA found in the mitochondria of cells and is only inherited through maternal lineages. Similarly, Chloroplast DNA is DNA found in the chloroplasts of plant cells.
A term that is used frequently in current research literature is Microsatellite DNA. Microsatellite DNA is a repeating series of DNA found randomly throughout the genome of organisms and which experiences a high rate of mutation. Not only is micro-satellite DNA the basis of DNA-fingerprinting used in paternity and crime cases, but it also allows population geneticists to detect even small genetic differences between populations.
Population genetics has application to evolutionary biology, conservation biology, and public health. When the allele frequencies in a population change over time, the population is said to have evolved. Evolutionary biologists use population genetics to determine whether a population has evolved and examine the processes responsible for that change.
When a population has been reduced to a small number of individuals, the number of alleles in the gene pool also has been reduced. This is of concern for conservation biologists because those alleles are the basis of genetic variability and allow a species to adapt to and survive in a changing environment. Even if an endangered species rebounds from the brink of extinction, it may still be vulnerable because of low genetic variability within the population.
Population genetics allows public health officials to determine the frequency of deleterious alleles in the population. As more diseases are found to have a genetic basis, population genetics will become increasingly important in preventative health care. For example, two of the genes responsible for genetic breast cancer, BRCA1 and BRCA2, have been found to occur at higher than average frequencies among Jewish women. This information can alert physicians to take extra precautions when screening their Jewish patients for breast cancer.
4. RESEARCH LITERATURE CONNECTION Print Version
Brown, L.N. 1965. Selection in a population of house mice containing mutant individuals. Journal of Mammalogy 46 (3): 461-465.
Christensen, A.C. 2000. Cats as an aid to teaching genetics. Genetics 155: 999-1004.
Cowen, L.E., D. Sanglard, D. Calbrese, C. Sirjusingh, J.B. Anderson, and L.M. Kohn. 2000. Evolution of drug resistance in experimental populations of Candida albicans. Journal of Bacteriology 182 (6): 1515-1522
Keyghobadi N., J. Roland and C. Strobeck. 1999. Influence of landscape on the population genetic structure of the alpine butterfly Parnassius smintheus (Papilionidae). Molecular Ecology 8: 1481-1495
Zajc, I., C.S. Mellersh, and J. Sampson. 1997. Variability of canine micro-satellites within different dog breeds. Mammalian Genome 8: 182-185
