Bio171-F10-Lec 24 - Biology 171 Monday, November 8, 2010...

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Unformatted text preview: Biology 171 Monday, November 8, 2010 Lecture 24: Species & Speciation Announcements Text Reading Lecture 24 : 4 th : Chapter 26 (458-471) 3 rd : Chapter 26 (526-541) Lecture 25 : 4 th : Chapter 27 (474-479) 3 rd : Chapter 27 (543-548) Species Concepts Allopatric Speciation: Sympatric Speciation Prezygotic Barriers to Gene Flow Postzygotic Barriers to Gene Flow Speciation by Polyploidy Testing Speciation This Week in Discussion: Sexual Selection/Speciation 1 Germline base substitution mutations occur more frequently in males than in females, especially in older males. The main explanation for the sex and age effect is that a much larger number of germline divisions occurs in the male than in the female, and continues throughout male adulthood. Point mutations at some loci occur almost exclusively in males , whereas others have a smaller excess, roughly ten times more than in females . Which is more typical remains to be determined. 26 In this particular condition, a protein called the "Fibroblast Growth Factor Receptor" functions abnormally. The result is that the growth of bones, which normally occurs in the cartilage of the growth plate, is slowed. This leads to shorter bones, abnormally shaped bones, and shorter stature. Heterozygotes have a normal life span and intelligence; homozygotes typically die before or shortly after birth. Caused by mutations in the transmembrane domain of the fibroblast growth factor receptor 3 (FGFR3): 153 of 154 analyzed cases are due to a glycine to arginine substitution at codon 1,138 of the gene. Achondroplasia Dr. Michael Ain Johns Hopkins University 27 In the Roloff family, mom Amy and son Zach carry the allele for achondroplasia. Dad Matt has a different form of dwarFsm not inherited by his children. 28 Indian teenager Jyoti Amge is thought to be the worlds shortest person with achondroplasia. Shown here with school classmates, she is now 16. She is 1ft, 11 inches tall and weighs 11 pounds. 29 The ordinate is the ratio of the observed number of mutations (O) to the number expected (E), if all paternal ages are associated with the same frequency of mutation. In other words, it should flatline at 1.0 if there is no paternal age effect The blue line gives the actual data; the red line is the best-fitting exponential curve. Relative frequency of de novo achondroplasia at different paternal ages O/E In an independent study, the parental origin of achondroplasia mutations was determined for 40 sporadic cases. All 40 occurred on the paternal chromosome. 30 2 Recognition of species boundaries in natural populations can be surprisingly difFcult. In essence, it hinges on the intertwined attributes of common descent, reproductive continuity and possession of diagnostic characteristics....
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This note was uploaded on 02/13/2012 for the course BIO 171 taught by Professor Josephinekurdziel during the Fall '08 term at University of Michigan.

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Bio171-F10-Lec 24 - Biology 171 Monday, November 8, 2010...

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