WZ BISC 120 Sept. 14

WZ BISC 120 Sept. 14 - Evolution of Populations Biological...

Info iconThis preview shows pages 1–17. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Evolution of Populations Biological Sciences 120 Lecture 7, Sept. 14 Wiebke Ziebis Chapter 23 short • Natural selection acts on individuals, but only populations evolve • Genetic variations in populations contribute to evolution • Two processes, mutation and sexual reproduction, produce the variation in gene pools that contributes to differences among individuals Genetic Variation • Variation in individual genotype leads to variation in individual phenotype • Not all phenotypic variation is heritable • Natural selection can only act on variation with a genetic component Fig. 23-2 (a) (b) Variation Within a Population • Both discrete and quantitative characters contribute to variation within a population • Discrete characters can be classified on an either-or basis • Quantitative characters vary along a continuum within a population Variation Between Populations • Most species exhibit geographic variation , differences between gene pools of separate populations or population subgroups Fig. 23-3 13.17 19 XX 10.16 9.12 8.11 1 2.4 3.14 5.18 6 7.15 9.10 1 2.19 11.12 13.17 15.18 3.8 4.16 5.14 6.7 XX • Some examples of geographic variation occur as a cline , which is a graded change in a trait along a geographic axis Fig. 23-4 1.0 0.8 0.6 0.4 0.2 46 44 42 40 38 36 34 32 30 Georgia Warm (21°C) Latitude (°N) Maine Cold (6°C) Ldh-B b allele frequency Mutation • Mutations are changes in the nucleotide sequence of DNA • Mutations cause new genes and alleles to arise • Only mutations in cells that produce gametes can be passed to offspring Mutations That Alter Gene Number or Sequence • Chromosomal mutations that delete, disrupt, or rearrange many loci are typically harmful • Duplication of large chromosome segments is usually harmful • Duplication of small pieces of DNA is sometimes less harmful and increases the genome size • Duplicated genes can take on new functions by further mutation Sexual Reproduction • Sexual reproduction can shuffle existing alleles into new combinations • In organisms that reproduce sexually, recombination of alleles is more important than mutation in producing the genetic differences that make adaptation possible Concept 23.2: The Hardy-Weinberg equation can be used to test whether a population is evolving • The first step in testing whether evolution is occurring in a population is to clarify what we mean by a population Gene Pools and Allele Frequencies • A population is a localized group of individuals capable of interbreeding and producing fertile offspring • A gene pool consists of all the alleles for all loci in a population • A locus is fixed if all individuals in a population are homozygous for the same allele Fig. 23-5 Porcupine herd Porcupine herd range Beaufort Sea N O R T H W E S T T E R R I T O R I E S MAP AREA A L A S K A C A N A D A Fortymile herd range Fortymile herd A L A S K A Y U K O N One species Two populations • The frequency of an allele in a population can...
View Full Document

This document was uploaded on 02/14/2011.

Page1 / 57

WZ BISC 120 Sept. 14 - Evolution of Populations Biological...

This preview shows document pages 1 - 17. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online