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Speciation & Homology Descent with modification modified characteristic = homology Speciation produces “sister species” descended from a common ancestor. Descendant species retain characteristics of common ancestor possibly in modified form.
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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