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.

How is microevolution studied? How is phenotypic variation measured? Key Ideas How is microevolution studied? How is phenotypic variation measured? How are genetic variation and change measured? How does genetic variation originate?

What kinds of variation can be seen in this photograph? 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. variation in flower color and plant height

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.

What do we now know about heredity that Darwin did not know? We know about genetics, such as how genotype relates to phenotype. Visual Concept: Population

Eye color is a polygenic character Eye color is a polygenic character. Different genes control different pigments, which combine to produce various shades of blue, green, or brown. 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.

Visual Concept: Single Allele, Multiple Allele and Polygenic Traits

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.

Why do polygenic characters vary so much? because many unique combinations of alleles are possible Normal Distribution How do the number of genes for a character relate to its variation? The more genes that affect a character, the more variations there can be.

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.

What is the main measure of genetic variation? frequency of alleles Visual Concept: Population and Gene Movement

Genotype Frequencies Vs. Allele Frequencies Is the dominant allele always the most frequent? No. Even if an allele is dominant, it may not be the most frequent allele in a population.

Sources of Genetic Variation Why is mutation so important? because it is the source of variation in populations 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. Visual

(frequency of EE) + (frequency of Ee) + (frequency of ee) = 1 Genotype Frequencies (frequency of EE) + (frequency of Ee) + (frequency of ee) = 1 (frequency of E) + (frequency of e) = 1 What is the sum of all allele frequencies for any one gene? 1 or 100%

C. a phenotypic variation D. a gene pool Exit Question The sum of all allele frequencies in a population at any time is called ______. A. polygenic B. genotype frequency C. a phenotypic variation D. a gene pool