26_Lecture_Presentation

26_Lecture_Presentation - Concept 24.4: Speciation can...

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Concept 24.4: Speciation can occur rapidly or slowly and can result from changes in few or many genes The Time Course of Speciation Broad patterns in speciation can be studied using the fossil record, morphological data, or molecular data The fossil record includes examples of species that appear suddenly, persist essentially unchanged for some time, and then apparently disappear
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Patterns in the Fossil Record Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibria to describe periods of apparent stasis punctuated by sudden change The punctuated equilibrium model contrasts with a model of gradual change in a species’ existence (a)Punctuated pattern Time (b) Gradual pattern
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Speciation Rates The punctuated pattern in the fossil record and evidence from lab studies suggest that speciation can be rapid For example, the sunflower Helianthus anomalus originated from the hybridization of two other sunflower species The interval between speciation events can range from 4,000 years (some cichlids) to 40 million years (some beetles), with an average of 6.5 million years
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Figure 24.19 H. annuus gamete H. petiolarus gamete F 1 experimental hybrid (4 of the 2 n = 34 chromosomes are shown) EXPERIMENT RESULTS Chromosome 1 H. anomalus Chromosome 2 H. anomalus Experimental hybrid Experimental hybrid
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Studying the Genetics of Speciation A fundamental question of evolutionary biology persists: How many genes change when a new species forms? Depending on the species in question, speciation might require the change of only a single allele or many alleles For example, in Japanese Euhadra snails, the direction of shell spiral affects mating and is controlled by a single gene In monkey flowers ( Mimulus ), two loci affect flower color, which influences pollinator preference Pollination that is dominated by either hummingbirds or bees can lead to reproductive isolation of the flowers In other species, speciation can be influenced by larger numbers of genes and gene interactions
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From Speciation to Macroevolution Macroevolution is the cumulative effect of many speciation and extinction events
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Studying genetic mechanisms of change can provide insight into large-scale evolutionary change Genes that program development control the rate, timing, and spatial pattern of changes in an organism’s form as it develops into an adult Concept 25.5: Major changes in body form can result from changes in the sequences and regulation of developmental genes
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Changes in Rate and Timing Heterochrony is an evolutionary change in the rate or timing of developmental events It can have a significant impact on body shape The contrasting shapes of human and chimpanzee skulls are the result of small changes in relative growth rates Chimpanzee infant Chimpanzee adult Chimpanzee adult Human adult Human fetus Chimpanzee fetus
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Heterochrony can alter the timing of reproductive development relative to the development of
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This note was uploaded on 12/14/2011 for the course BISC 13004 at USC.

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26_Lecture_Presentation - Concept 24.4: Speciation can...

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