Class Notes (835,629)
Canada (509,297)
Biology (1,284)
BIOL 103 (255)
Lecture

Variation and Natural Selection Continued.docx

2 Pages
58 Views
Unlock Document

Department
Biology
Course
BIOL 103
Professor
Peter T Boag
Semester
Winter

Description
Variation and Natural Selection - Genetic Variation in populations is caused by: o Mutation (e.g. UV light hitting skin cells)  Changes in DNA sequences  new alleles  Cannot enter population unless in gametes o Sexual reproduction  variable gametes  Meiosis shuffles maternal and paternal chromosomes into new combinations  Crossing over shuffles alleles into new combinations on each chromosome  Result is genetic and phenotypic variation even in absences of new mutations - Shuffling of homologous chromosomes and crossing over in meiosis leads to new gene combinations and variable gametes - Sex promotes variation: o In an organism with three chromosomes per haploid set (n =3), 8 gamete types result from randomly grouped maternal and paternal chromosomes o A diploid organism produces 2 maternal and paternal chromosome combinations (n = haploid chromosome number) o With n=23, a human can produce 2 = 8.4 million different gametes (not including recombination or mutation) - The persistence of sexual reproduction in natural populations  unsolved problems for evolutionary biology - In theory: male-producing, sexual populations are subject to invasion and rapid replacement by clonal females - Population of one million sexual individuals would be replaced in less than 50 generation by a clone beginning with a single asexual female - New molecular techniques in 1960’s showed large amounts of genetic variation o New techniques such as protein electrophoresis revealed more variation than expected; excess variation = genetic load o Genetic polymorphism maintained by:  Balanced polymorphisms, where heterozygotes are more fit than either homozygote  Frequency dependent selection, where fitness depends on the relative abundance of a morph  Neutrality, e.g. not being exposed to selection o Also spatial/temporal environmental variation; but resulting geographic variation in phenotype may have a genetic and/or environmental origin – need to test o Environment also affects developing phenotypes of quantitative
More Less

Related notes for BIOL 103

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