Bio171-F11-Lec 26 - Biology 171 Monday, November 7, 2011...

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Biology 171 Monday, November 7, 2011 Announcements Text Reading Lecture 26 : Chapter 26 (458-471) Lecture 27 : Chapter 27 (474-479) Male Driven Mutation (end) Species Concepts Allopatric & Sympatric Speciation Prezygotic Barriers to Gene Flow Postzygotic Barriers to Gene Flow Speciation by Polyploidy Testing Speciation This Week in Discussion: Review HWE; Evolution in Sticklebacks Exam 3 – Wed. Nov. 16 8-10 PM.
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We can estimate the number of germ-cell divisions in a male as follows. There are an estimated 30 cell divisions before puberty and then one stem cell division every 16 days, or 23 per year. A sperm produced by a man of age 40 has gone through 610/23, or more than 25 times as many chromosome replications as an egg. Conversely, for a man of age 20, this number is only about 7 times as many.
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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.
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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
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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.
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Indian teenager Jyoti Amge is thought to be the world’s shortest person with achondroplasia. Shown here with school classmates, and her parents, she is now 17. She is 2ft tall and weighs 11 pounds.
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(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
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Bio171-F11-Lec 26 - Biology 171 Monday, November 7, 2011...

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