Turner College & Career High School 2016
Biological Diversity Turner College & Career High School 2016 Speciation & Homology Descent with modification
modified characteristic =homology Speciation produces sisterspecies descended from acommon ancestor. Descendant species retaincharacteristics of commonancestor possibly inmodified form. Genealogical Relationship
Evidence of common ancestry. Same characteristics in 2 or more species inherited from a common ancestor = homology. Possibly/probably modified since split from sister species. The common ancestor no longer exists, so how can we tell whats a homology and whats not? Criteria for Homology Position in relation to other body structures.
Embryonic origin Continuity: characteristics homologous to another characteristic are homologous to each other. Criteria for Homology Position in relation to other body structures.
Forelimbs Humerus, radius & ulna, carpals, metacarpals, phalanges Criteria for Homology Position in relation to other body structures.
Insect wings, legs Antennae Criteria for Homology Position in relation to other body structures.
Flower parts Sepals Petals Stamen stamen Criteria for Homology Embryonic origin similar developmental origin.
Pharyngeal arch: jaw Limb buds Lobes of brain Heart & arteries Gill slits Tail Criteria for Homology Continuity: characteristics homologous to another characteristic are homologous to each other. Dentary Inner Ear Homology Provides Evidence for Evolution
Comparative Anatomy Comparative Embryology Comparative Fossil Anatomy Comparative Physiology & Biochemistry Comparative Anatomy Modification of existing characteristics/organs for other functions. Wings in bat Whale flippers Human arm Turtle leg Comparative Anatomy Modification of existing characteristics/organs for other functions. Teeth: fangs in rattlesnake Salivary gland: venom gland Comparative Anatomy Imperfection of adaptation.
Panda's thumb: actually radial sesamoid bone. "Oh, my aching . . ." after 2-3 million years, we are still subject to back strain. Comparative Anatomy Modification but without function.
Vestigial organs: senseless signs of history. Rudimentary structure in organism corresponding to a functional structure or organ in ancestral organism. Appendix in humans Comparative Anatomy Vestigial organs Pelvic bones in whales. Comparative Anatomy Vestigial organs Coccyx (tailbone) in humans. Comparative Anatomy Vestigial organs Nictitating membrane in humans.
In animals, it is a clear eyelid can be drawn across the eyeball for protection from debris, prey, or the dryness of air, similarly to regular eyelids. Nictitating membrane Comparative Embryology
Some traits seen only in embryos or larvae. Homology with larval or adult traits in other organisms. Notochord in vertebrates. Notochord & dorsal nerve cord in tunicate larvae. Bilateral symmetry in echinoderm larvae Comparative Embryology Comparative Fossil Anatomy
The fossil record. Homology relates fossils to existing organisms. Change in lineages Extinction Example: horses Comparative Fossil Anatomy
Homology relates fossils to existing organisms. Change in lineages Extinction Example: trilobites Comparative Physiology & Biochemistry
Homology applies to physiological & metabolic processes. Glycolysis and Krebs cycle Mechanisms of cell signaling Homology applies to biochemicals. DNA as genetic code RNA to translate code into protein structure ATP as energy currency of cells Other Factors in Evolution Convergence Evolution (adaptation) of dissimilar organisms to common function, superficially similar characteristics. Piercing sucking mouth in bugs, mosquitoes, fleas, butterflies Wings in bird, bat, pterosaur, insect (airplane?) Convergent characteristic NOT present in common ancestor. Convergence Biogeography Organisms have evolved independently indifferent parts of the world. Geographic distributions of species, genera,families, etc. Biogeography Organisms have evolved independently in different parts of the world. Endemic species, genera, etc. on islands. Galapagos finches Biogeography Biogeography Used with fossil record to reconstruct evolutionary history. Camels in Asia: camel, dromedary South America: llama, alpaca Camels in N. America? Fossils? Biogeography: Alligator in SE USA and China/SE Asia.
Hellbenders in SE USA and China. Cyclocosmia in SE USA and Malaysia. Biogeography Isthmus of Panama divided Caribbean from Pacific about 3 million years ago. Previously a body of water existed. Several species crabs, snails, fish, etc. have nearest relatives on other side of land barrier. Natural Selection, Genetic Drift & Gene Flow Evolutionary Change Natural selection Genetic drift Gene flow
Three major factors alter allele frequenciesand bring about most evolutionary change: Natural selection Genetic drift Gene flow Natural Selection Differential success in reproduction results in certain alleles being passed to the next generation in greater proportions. For example, an allele that confers resistance to DDT increased in frequency after DDT was used widely in agriculture. Natural Selection Genetic Drift The smaller a sample, the greater the chance of deviation from a predicted result. Genetic drift describes how allele frequencies fluctuate unpredictably from one generation to the next (chance). Genetic drift tends to reduce genetic variation through losses of alleles. Genetic Drift 5 plants leave off- spring Generation 1
CRCR CRCR 5 plants leave off- spring CRCW CWCW CRCR CRCW CRCR Figure 23.9 Genetic drift. CRCW CRCR CRCW Generation 1 p (frequency of CR) = 0.7 q (frequency of CW) = 0.3 Genetic Drift 5 plants leave off- spring 2 plants leave off- spring
CRCR CRCR 5 plants leave off- spring CWCW CRCR 2 plants leave off- spring CRCW CRCW CWCW CRCR CRCR CWCW CRCW CRCW CRCR Figure 23.9 Genetic drift. CRCW CWCW CRCR CRCR CRCW CRCW CRCW Generation 1 p (frequency of CR) = 0.7 q (frequency of CW) = 0.3 Generation 2 p = 0.5 q = 0.5 Genetic Drift 5 plants leave off- spring 2 plants leave off- spring
CRCR CRCR 5 plants leave off- spring CWCW CRCR 2 plants leave off- spring CRCR CRCW CRCW CRCR CRCR CWCW CRCR CRCR CWCW CRCR CRCR CRCW CRCW CRCR CRCR CRCR Figure 23.9 Genetic drift. CRCW CWCW CRCR CRCR CRCR CRCW CRCW CRCW CRCR CRCR Generation 1 p (frequency of CR) = 0.7 q (frequency of CW) = 0.3 Generation 2 p = 0.5 q = 0.5 Generation 3 p = 1.0 q = 0.0 The Founder Effect The founder effect occurs when a few individuals become isolated from a larger population. Allele frequencies in the small founder population can be different from those in the larger parent population. The Bottleneck Effect Sudden reduction in population size due to a change in the environment. New gene pool may not reflect original. If the population remains small, it may be further affected by genetic drift. Original Population Bottleneck Effect Surviving Population Case Study: Impact of Genetic Drift on the Greater Prairie Chicken
Loss of prairie habitat = reduction of population. The surviving birds had low levels of genetic variation, and only 50% of their eggs hatched. Impact of Bottleneck Effect
Pre-bottleneck (Illinois, 1820) Post-bottleneck (Illinois, 1993) Location Pop. Size Number of Alleles/Locus Percentage of Eggs Hatched Illinois 1993 1,000-25,000