Section1: Genetic Variation Preview • Bellringer • Key Ideas • Population Genetics • Phenotypic Variation • Measuring Variation and Change • Sources of Genetic Variation • Summary
Bellringer Imagine that you are in charge of a goat ranch. The cost of fencing is high, so you must implement a breeding program that will produce shorter-legged goats within the next 20 years. Write down how you would meet this goal.
Key Ideas • How is microevolution studied? • How is phenotypic variation measured? • How are genetic variation and change measured? • How does genetic variation originate?
Population Genetics • Charles Darwin knew that heredity influences characteristics, but he did know about genes. • We can now study and predict genetic variation and change that underlie evolution. • Microevolution is evolution at the level of genetic change in populations.
Population Genetics, continued • Microevolution can be studied by observing changes in the numbers and types of alleles in populations, called population genetics. • The study of genetics and evolution are advancing together. • The link from microevolution to macroevolution—speciation—can be studied in detail.
Phenotypic Variation • The variety of phenotypes that exists for a given characteristic depend on how many genes affect it. • Polygenic characters are influenced by several genes. Examples include human eye color and height. • Biologists study polygenic phenotypes by measuring each individual in the population and then analyzing the distribution of the measurements.
Phenotypic Variation, continued • A distribution is an overview of the relative frequency and range of a set of values. • Often, some values in a range are more common than others. • A normal distribution, or bell curve, is one that tends to cluster around an average value in the center of the range.
Measuring Variation and Change • The particular combination of alleles in a population at any one point in time makes up a gene pool. • Genetic variation and change are measured in terms of the frequency of alleles in the gene pool of a population. • A frequency is the proportion or ratio of a group that is of one type. To study genetic change, the frequency of each allele in a population can be tracked over time.
Sources of Genetic Variation • Evolution cannot proceed if there is no variation. The major source of new alleles in natural populations is mutation in germ cells. • Mutation generates new alleles at a slow rate. • Only mutations in germ cells (egg and sperm) are passed on to offspring.
Summary • Microevolution can be studied by observing changes in the numbers and types of alleles in populations. • Biologists study polygenic phenotypes by measuring each individual in the population and then analyzing the distribution of the measurements. • Genetic variation and change are measured in terms of the frequency of alleles in the gene pool of a population. • The major source of new alleles in natural populations is mutation in germ cells.