Class Notes (836,580)
Canada (509,856)
Biology (844)
BIOL 121 (154)
All (30)
Lecture

Biol 121- 2010.03.12- Evolution- Natural Selection (Ch. 24).docx

3 Pages
138 Views
Unlock Document

Department
Biology
Course
BIOL 121
Professor
All Professors
Semester
Fall

Description
Biol 121 225 Freeman 491-500 Mar. 12, 10 Natural Selection, Ch. 24 Natural selection -credit for ‘natural selection’ is given to Darwin -first proposed by -Lamarck and others had already proposed evolution as a pattern in nature -used to explain before Darwin began his work but Darwin had the crucial insight of seeing natural selection that could be used to explain pattern of descent with modification -four simple postulates/steps 1) Variation in a pop- Individual organisms that make up a pop vary in traits they possess, like size or shape 2) Heritable traits involved - Some trait differences are heritable, so passed on to offspring genetically 3) Variable fitness - In each generation, many more offspring are produced than can possibly survive -therefore only some individuals in the pop survive long enough to produce offspring, and among individuals that produce offspring, some produce more than others 4) Fitness due to heritable traits - Subset of individuals that survive best and produce the most offspring is not a random sample of the pop -individuals with certain heritable traits are more likely to survive + reprod -natural selection occurs when indiv with certain char produce more offspring than do indiv w/o those characteristics The outcome of these four steps -Evolution – change in genetic char of a pop over time is the outcome of these four steps -variation among individuals is necessary for evolution -populations must change over time for evolution to occur Summing up the 4 steps in only 2 Evolution by natural selection occurs when 1) heritable variation leads to… 2) differential success in survival and reproduction Allele frequencies WRT evolution -evolution can be defined as a change in allele frequencies in a pop over time Example with light and dark winged -two alleles for a gene for wing colour, one producing dark and other light moths -predation by birds – they eat dark-winged individuals much more readily than they can find and eat light-winged individuals if have light-coloured bark -therefore, predation by birds causes natural selection on wing colour leading to differential success -therefore, the allele for light coloured wings increases in the pop Darwinian fitness -ability of an individual to produce offspring (relative to that ability in other indiv in the pop) – this is a measurable quantity. How? count how many offspring it produces relative to other individuals Adaptation -when some individuals have a heritable trait that increase their fitness in their specific environment, that trait is naturally selected -the pop evolves and adapts to the specific environment Acclimatization -short term change in an individual and not passed on to offspring e.g. wood frogs in North Am. -wood frogs exposed to extreme cold in winter -ice forms in their skin and their bodies produce some sort of natural antifreeze, protecting their tissues -this is change in individual’s phenotype that occur in response to changes in environmental conditions -this phenotypic change is not passed on to the offspring, therefore no evo. Penicillin and resistance (WRT -this is an example of antibiotic resistance evolution) -penicillin – antibiotic/drug that blocks cell wall formation in some bacteria -resistant strains have a gene for lactamase in a plasmid  this breaks down penicillin -therefore, this trait is naturally selected b/c it increases fitness, and as the 1 Biol 121 225 Freeman 491-500 Mar. 12, 10 pop evolves, the allele frequency for this trait increases over time -the population then becomes resistant, and can also transfer the plasmid Mycobacterium tuberculosis -this causes tuberculosis and has been doing so in humans for >1000 yrs, leading to the lung infection disease -in the 1950s, the prevalence of this disease decreased b/c new drugs, healthier people, etc -but in the late 1980s, the number of cases started to increase -Rifampin – antibiotic to treat TB by binding to RNA polymerase and thereby interfering with transcription -a point mutation occurred which change leucine to serine in the AA sequence of RNAP -this allows transcription even in the presence of Rifampin  drug resistance -bacteria become resistant fast because they divide fast Galapagos finches – medium ground
More Less

Related notes for BIOL 121

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit