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Chapter 16

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Tristan Long

Chapter 16 Microevolution Genetic Changes within PopulationsMicroevolution heritable change in the genetic makeup of a population oCharles Darwin noticed importance of variation within population and noticed population can change from one generation to next due to environmental pressure Population all the individuals of a single species that live together in the same place and time 161 Variation in Natural Populations Phenotypic variation differences in the appearance or function that are passed down oCaused by genetic differences between individuals differences in environmental factors or both genetic and environmental oBecause environment can influence expression of genes phenotype interaction between both environment and genetic 1How to test it change the environment of the same genetic item and see if phenotype changes oResult genetic and phenotypic variations not perfectly correlated oEx Flowers with same genotype vary in colour depending on the acidity of soil Quantitative variation individuals differ in small incremental ways oMost exhibit this oEx If you weighed everyone in biology class notice that from heaviest to lightest mass varies almost continuously oBell shaped curve where width of curve rep variability among individualsQualitative variation exist in 2 or more discrete states and intermediate forms are often absent oEx Snow geese either have blue or white feathers oMendel inferred the genetic bases of qualitative traits such as flower colour in peas by crossing plants with different phenotypesPolymorphism existence of discrete variants of a character oEx One type of snail group varies in colour stripes size in shelloEx Human blood types ABABOoDescribe phenotypic polymorphisms quantitatively by calculating frequency Only genetic based variation is subject to evolutionary change Artificial selection population expressing quantitative traits that have a genetic basis can be selectively bred to change the average value of the trait oEx Noticed house mice that run on the wheel more are more active and run faster so they selectively bred these mice to produce a line of mice that are faster and more active compared to the normal mouse proving the difference in activity level has a genetic bases Genetic variation raw material moulded by micro evolutionary processes o2 potential sources production of 2 alleles and rearrangement of existing alleles oMost small scale alleles arise from small scale mutations oRearrangement of existing alleles into new combinations can result from larger scale changes in chromosome structure and several forms of genetic recombination such as1Crossing over between homologous chromosomes during meiosis 2Independent assortment of nonhomologous chromosomes during meiosis 3Random fertilizations between genetically different sperm and egg
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