Chapter 22 Descent with Modification What is Evolution and Adaptation Evolution two main ideas o Change over time of the genetic composition of a population o Decent of modern organisms with modification from preexisting organisms Evolutionary adaptation o Accumulation of inherited characteristics that enhance organisms ability to survive in specific environments Organisms have traits that allow them to survive better on average than other individuals in the environment the adaptations will most likely be passed on to offspring Pre Darwinian Theory of Evolution Lamarck s Ideas o Use and disuse bodies of living organisms are modified through the o Inheritance of acquired characteristics these modifications are use or disuse of parts inherited by offspring o These ideas turned out to be wrong o Lamarck gave the example of giraffes and their neck length he said that the lifetime of stretching to reach leaves on trees were passed onto offspring However because the giraffes did that doesn t mean the traits were passed on because it was something they modified in their lifetimes Evolution by Natural Selection Darwin and Wallace developed the theory independently Charles Darwin voyage of the Beagle o Darwin took a five year voyage on the Beagle and overtime developed ideas on evolution and how organisms developed He developed the process of natural selection Alfred Russell Wallace naturalist in Indonesia o Wallace studied birds in Indonesia By focusing on the traits of bird species he was studying he also came up with the idea of natural selection Natural Selection The unequal survival and reproduction of organisms due to environmental forces resulting in the preservation of favorable adaptations o Some organisms have traits that allow them to survive better than other individuals They then pass these traits onto their offspring Process selects from what is available in the gene pool New characteristics are not created on demand Natural selection relies on variability of a population what is available in the gene pool at the time It selects from the variability in the gene pool Mechanisms behind Natural Selection Figure from pg 458 Observations Inferences o Individuals in a population vary in their heritable characteristics o Organisms produce more offspring than the environment can support o Individuals that are well suited to their environment tend to leave more offspring than other individuals o Over time favorable traits accumulate in the population Artificial Selection Selective breeding of organisms to encourage the occurrence of desirable traits Analogous to natural selection Figure 22 9 Concept 22 3 Evolution is supported by an overwhelming amount of scientific evidence Figure 22 13 o Example of natural selection o Soapberry bugs primary food source were vine fruit Their beak would be inserted to the fruit to draw nutrients from seeds The beak size was correlated to their feeding success As they began eating golden rain fruit their beak size decreased because they didn t need to penetrate as large of a seed Drug resistant viruses are examples of natural selection because the resistant strands survive and reproduce so that only they are left Homologous and Analogous Structures Homologous structures or other attributes in different species that resemble each other because of common ancestry Analogous structures that are similar in function but not in structure and developmental and evolutionary origin Figure 22 15 structure In class example analogous analogous o Homologous structures in mammalian forelimbs o The underlying bone structure in the examples is the same They all have a humorous radius ulna carpals metacarpals and phalanges o The examples use the structures in different ways but have the same o The wings of a dragonfly and bird are not homologous but analogous o The wing of a dragonfly and flipper of a seal are not homologous or o The flipper of a seal and penguin are homologous and analogous o The flipper of a penguin and wing of a bird are homologous not All vertebrates share similar developmental genes Differences arise by some genes being switched on or off at varying times Homologous Structures Vertebrate Embryos during development Figure 22 16 Biochemistry and Molecular Biology DNA is universal genetic material All life forms use approximately the same 20 amino acids to make proteins All use ATP as the primary form of cellular energy All use RNA and ribosomes to make protein Figure 22 19 o Phylogenetic tree shows relationships among different organisms by looking at homologies found in those organisms o At each branch is the shared feature of the homologous organisms Convergent Evolution Convergent evolution similarity between two organisms structures or molecules due to independent evolution along similar lines rather than descent from a common ancestor Figure 22 18 o The flaps of skin connecting the limbs of flying squirrels are sugar gliders were not shared with their ancestors they developed overtime Chapter 23 The Evolution of Populations The Smallest Unit of Evolution One common misconception about evolution is that individual organisms evolve during their lifetime Evolutionary processes i e natural selection acts on individuals but populations evolve There are changes in the frequencies of genes in a population over time Genetic Variation makes Evolution Possible Mutation Mutations changes in nucleotide sequence of DNA o Source of new alleles and genes Point mutation change in one nucleotide base in a gene Chromosomal mutations delete disrupt or rearrange many loci on a chromosome Gene duplications duplication of whole segments of a chromosome Mutation rate averages 1 in every 100 000 genes per generation Sexual Recombination In sexually reproducing organisms sexual recombination produces most of the variability in each generation Variation within a Population Discrete characters classified on an either or basis o Example flower color in pea plants Quantitative characters vary along a continuum within a population o Example height weight The Hardy Weinberg Equation The Hardy Weinberg equation can be used to test whether a population is o Population a group of individuals of the same species living in a evolving Populations certain defined area o Figure 23 6 Hardy Weinberg Equilibrium frequencies don t change H W Equilibrium describes a population that is not evolving i e allele Five assumptions behind H W Equilibrium o No mutations o Large population size
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