Download - Chapter 20 Evolution of Genes and Traits
![Page 1: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/1.jpg)
Chapter 20Evolution of Genes and
Traits
Darwinian evolution, mutations and molecular evolution, a case study in natural selection, morphological evolution; the origin of new genes and protein functions
![Page 2: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/2.jpg)
Major principles of Darwinian evolution
• Principle of variation—among individuals in a population, variation exists
• Principle of heredity—offspring resemble parents more than unrelated individuals
• Principle of selection—some forms more successful at survival and reproduction in a given environment (natural selection)
• heritable variationheritable differences between populations over time
![Page 3: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/3.jpg)
Phyletic evolution – continuous change over time in a single line of descent
Diversification – the origin of new species over time
![Page 4: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/4.jpg)
Darwin’s Finches and Adaptive Radiation
A phylogenetic tree is a visual representation in tree form of how we think evolution has occurred, often based on fossils.
Famous example:Galapagos finches, with numerous feeding adaptations
![Page 5: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/5.jpg)
Neo-Darwinian evolution—Darwin’s principles w/genetics, population
biology
![Page 6: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/6.jpg)
Different models of selection
• Directional selection- pushes population toward homozygosity and phenotypes toward one extreme
• Balancing selection- favors heterozygotes but maintains all phenotypes
• Disruptive selection- favors both homozygotes, eliminates heterozygotes and increases extremes of phenotypes
![Page 7: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/7.jpg)
Mutations and Molecular Evolution
• 3 different effects on fitness by mutations:– deleterious– increase efficiency or performance– no effect (“neutral”)
• can be a little more specific:– effectively neutral mutationsselection intensity so
low that mutation is retained– effectively selected mutationsselection high enough
that mutation is weeded out
![Page 8: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/8.jpg)
Synonymous changes refer to a mutation which substitutes the same amino acid
Deleterious mutations removed by purifying selection-shown by lower rate of nonsynonymous mutations
Mutation rate of synonymous sites higher than nonsynonymous
![Page 9: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/9.jpg)
MOLECULAR CLOCKS: mutations/amino acid differences can be used to estimate evolutionary
divergence times
![Page 10: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/10.jpg)
Natural Selection in Action:An exemplary case
• Genotypes could be measured• The genetic and molecular basis of variation
was identified• The physiological role of the gene/protein
was well understood• The environmental (natural) selection
process was understood• We are talking about the connection
between sickle cell anemia and malaria
![Page 11: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/11.jpg)
Malaria Life Cycle
![Page 12: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/12.jpg)
Red blood cells in someone with sickle-cell trait
![Page 13: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/13.jpg)
Malarial parasites live within red blood cells
![Page 14: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/14.jpg)
Electrophoresis of hemoglobin variants
![Page 15: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/15.jpg)
The hemoglobin molecule
![Page 16: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/16.jpg)
The first seven N-terminal amino acids in normal and sickle cell hemoglobin
polypeptides
GAG
GUG
GLU = Glutamic acid is acidicVAL = Valine is neutral non-polar
![Page 17: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/17.jpg)
Gene frequency for HbS allele high in malaria (mosquitoes-rich) zones
HbAS heterozygous are more resistant to malaria
![Page 18: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/18.jpg)
Survival analysis of sickle-cell genotypes
![Page 19: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/19.jpg)
Morphological evolution-melanism in rock pocket mouse (adaptive changes)
![Page 20: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/20.jpg)
Morphological evolution—melanism in rock pocket mouse
• Pinacate region of SE Arizona has blackish lava rock areas interspersed with pale brown rock areas
• rock pocket mouse (Chaetodipus intermedius) has 2 melanic forms growing in 2 different substrates– dark form inhabits blackish areas– pale ancestral form lives in sand-colored areas
• Nachman et al. found 4 mutations in melanocortin 1 receptor (MC1R) gene of dark mice, causing protein to be constitutively active and lay down pigment constantly
![Page 21: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/21.jpg)
Morphological evolution—melanism in MC1R protein of
organisms
![Page 22: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/22.jpg)
Peppered Moths in Great Britain
![Page 23: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/23.jpg)
Morphological evolution-evolution of albinism in blind
cave fishes(gene inactivation)
![Page 24: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/24.jpg)
Morphological evolution—albinism in blind cave fishes
• albinism common in cave organisms (incl. fishes, crustaceans), often accompanied by eye loss
• genetic studies of Mexican blind cave fish (Astyonax mexicanus) in 2 different populations, Pachón and Molino, revealed different mutations in Oca2 gene—gene inactivation
• Pachón fishes are homozygous for deletion of intron and most of exon in Oca2 gene
![Page 25: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/25.jpg)
Morphological evolution-wing spots on fruit flies (regulatory sequence evolution)
Drosophila melanogaster
Drosophila biarmipes
![Page 26: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/26.jpg)
Origin of New Genes• New genes and proteins necessary for
wholly new functions and processes• Sources of new genes/DNA:
– Polyploidy-duplicate genomes can diverge– Gene duplications-duplicated genes can diverge– Transposition (transposable elements)– Retrotransposition (retrotransposons)– Imported DNA from organelles or horizontal
gene transfer
![Page 27: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/27.jpg)
The alternative fates of duplicated genes
![Page 28: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/28.jpg)
![Page 29: Chapter 20 Evolution of Genes and Traits](https://reader036.vdocuments.mx/reader036/viewer/2022081503/56815dc0550346895dcbea93/html5/thumbnails/29.jpg)
Final Thoughts• The one process now going on that will take millions
of years to correct is the loss of genetic and species diversity by the destruction of natural habitats. This is the folly our descendants are least likely to forgive us. --E. O. Wilson
• It's an important point to realize that the genetic programming of our lives is not fully deterministic. It is statistical - it is in any animal merely statistical - not deterministic. --Richard Dawkins
• If you liked genetics (PBIO 3300/5300), consider taking biotechnology and genetic engineering (PBIO 4500/5500) in the fall. –Allan Showalter