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Lecture 21 Notes

Lecture 21 Notes - In Table 1 how many of these causes of...

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In Table 1 , how many of these causes of death are related to old age ? Table 2: o Modifiable behavioral risk factors are leading causes of mortality in the U.S. o Nearly 50% of deaths in 2000 were caused by factors unrelated to age
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Vandan Desai BIOL 442—Developmental Biology 2 II. Evolutionary Hypotheses of Aging :: A. Antagonistic Pleiotropy Hypothesis (Medawar & Williams, 1950s)— i. Multiple genes exist, each w/ 2 or more alleles, that show antagonistic pleiotropy [alleles can have opposite effects ] = One allele promotes reproductive success in life, but w/ a price to pay later in early senescence The other allele of the same gene has the opposite effect ii. Natural selection favors the combination of alleles that is best suited for a particular population iii. Example: production of sex hormones in humans Enhanced production of androgen in men after puberty is beneficial for the production of strong bones , muscle , and sperm Things that tend to promote survival of species Later in life, androgen may contribute to hyperplasia or cancer of the prostate gland B. Disposable Soma Hypothesis (Kirkwood, 1996)— i. The sole function of the soma (body; non-germ cell) is to carry the germ line and this carrier function has evolved to be as economical as possible Don’t need to spend time/effort repairing the body ii. Predictions of this hypothesis = Organisms w/ a distinct germ line should show senescence, whereas organisms w/o a germ line should not Two annelid worms reproduce by transverse fission and don’t appear to senesce Maintenance and repair should operate at highest level in germ line Average mutation rate in human germ line = 4.4 x 10 -6 , smaller than the number for the soma Maintenance cost of the soma should increase w/ age III. Causes of Senescence :: A. Cell Division and the Shortening of Telomeres— i. Cells grown in culture have a limited capacity to proliferate Limited cell division means limited ability to renew cell populations ii. For normal fibroblasts, the number of cell divisions depend on the species and the age of the animal they were taken from: Fibroblasts from human infant = 60 doublings Fibroblasts from 80 year old human = 30 doublings iii. When cells stop dividing , they remain stuck in G 0 of the cell cycle
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