GENE20001 Lecture Notes - Lecture 29: Genetic Drift, Allele, Zygote
Darwin and Wallace
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Population includes individuals of varying phenotypes
○
Some phenotypes more successful at reproducing (higher fitness) in a given
environment
○
These phenotypes will increase in freq if selective advantage maintained
○
Darwin proposed
•
Diversity of species may result from adaptation. Darwin saw different beak phenotypes ate
different kinds of food and argued that some phenotypes were better adapted to eating a
particular food source
•
Modern description of natural selection relates molecular genetics to phenotypes
•
Within a population there is genetic variation from differences in DNA sequences.
1.
Some alleles may encode proteins that enhance an individual's survival or reproductive
capacity
2.
Individuals with beneficial alleles are more likely to survive and reproduce
3.
Over many gen allele freq of many different genes change through natural selection. Alters
characteristics of species. Net result is a population that is better adapted to its environment
and/or more successful at reproduction
4.
Promotes adaptation. Species continually screened by selective agents adapting to
environment
○
Buffers the species against effects of migration, mutation and genetic drift (acts
randomly with respect to fitness)
○
Explains diversity as it promotes the adaptation of various phenotypes to different
environmnts
○
Natural selection
•
Relative fitness components: mating success, fertility, fecundity (no. of eggs produced),
viability, development time (period of time where individual is reproductively active),
longevity (does not necessarily increase reproductive output) and IN PARTICULAR
ENVIRONEMT
•
Selective agents: factors in environment which discriminate b/w phenotypes and or genotypes
•
S is the selection against a genotype
○
•
Using component fitness
•
Departures from Mendelian expectations in laboratory crosses
•
Estimating fitness
In lab experiment a student examined effect of genotype of straw (s) locus on two fitness
•
Components of fitness
29 Natural Selection
Saturday, May 10, 2014
1:57 PM
Genetics Page 1
Document Summary
Some phenotypes more successful at reproducing (higher fitness) in a given environment. These phenotypes will increase in freq if selective advantage maintained. Darwin saw different beak phenotypes ate different kinds of food and argued that some phenotypes were better adapted to eating a particular food source. Modern description of natural selection relates molecular genetics to phenotypes. Within a population there is genetic variation from differences in dna sequences. Some alleles may encode proteins that enhance an individual"s survival or reproductive capacity. Individuals with beneficial alleles are more likely to survive and reproduce. Over many gen allele freq of many different genes change through natural selection. Net result is a population that is better adapted to its environment and/or more successful at reproduction. Species continually screened by selective agents adapting to environment. Buffers the species against effects of migration, mutation and genetic drift (acts randomly with respect to fitness)
