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16-1 GENETIC EQUILIBRIUM
Population genetics –evolution studied from genetic point of view
Microevolution – change in collective genetic material of population.
Population – smallest unit in which evolution will occur
Bell curve – shows most members of given population show given, measurable trait.
Only a FEW from the pop. Show extremes of the trait
In nature – quantitative measures (ie. Weight, height) tend to show variation in bell curve pattern
VARIATION IN TRAITS
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Family –varied but SIMILAR phenotypes –
because the members share some alleles!!
Environment (food available?)
Heredity
o Range of phenotypic choices vs. set of specific phenotype (all diff. heights vs. 2 colors)
VARIATION IN GENES
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Mutation – random change in gene passed on to offspring
Recombination – during meiosis – independent assortment & crossing over of genes on chromosomes, it’s when
the genes are reshuffled.
Random pairing of gametes – every organism makes so many gametes.. it’s random which ones will pair up
Scientists – still try to find what causes traits to vary - could depend on presence/absence of genes or factors in
environment
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When there are lots of alleles for lots of genes – there’s a VARIETY of genotypes and phenotypes
The Gene Pool
Gene pool – what population geneticists use to describe total genetic info available in a population
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Knowing all the genes in one pool & alleles *, you can predict expected genotypes and their frequencies for the
next generation.
Alleles: A, a, in set of 10 gametes.
5 gametes carry A, so allele frequency of A is 0.5 or 50% (allele frequency –
found by dividing number of certain allele by total number of allels of all type
in population [ 5/10])
Predicting Phenotype
Phenotype frequency – # of individuals with particular phenotype divided by total # of individuals in pop.
phenotypically diff, but
SAME ALLELE FREQUENCY
FREQUENCY of all genotypes expected in 2nd generation MUST ADD UP TO 1.0
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We know probabilities of getting RR and rr- so
Hardy-Weinberg Genetic Equilibrium
*phenotype frequencies can change like crazy from generation to another.
German physician Weinberg, British mathematician Hardy hardy-weinberg genetic equilibrium --showed
genotype frequencies will generally stay the same in population unless acted upon by outside influence
Based on these assumptions:
1. No net mutations occur; alleles stay the same
2. Individuals don’t enter/leave population
3. Population is LARGE
4. Individuals mate randomly
5. Selection doesn’t occur
True genetic equilibrium = THEORETICAL STATE
By showing how the equilibrium can be maintained, this principle helps us consider what forces DISRUPT THIS
EQUILIBRIUM