Chapter 16 Evolution of Populations. Section 16-2 Evolution As Genetic Change. Natural Selection. Does NOT Act Directly On Genes Does Act On Phenotypes The Phenotype Gives The Survival Edge Survivors Must Reproduce Alters Relative Frequency of Alleles Over Time. Evolution.
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Evolution As Genetic Change
Does NOT Act Directly On Genes
Acts On Populations
Does NOT Act On Individuals
Natural Selection On Single-Gene Traits Can Lead To Changes In Allele Frequencies And Thus To Evolution
What If Black Allowed The Lizard To Warm Up Faster & Move Quicker??????
Natural Selection Can Affect The Distribution Of Phenotypes In Any Of Three Ways:
When Individuals Near
The Center Of The Standard Curve Have Higher Fitness
Than Individuals On Either End
May Narrow The Curve
Example: Human Birth Weight
When Individuals At The
Upper And The Lower End
Have Higher Fitness Than Individuals Near The Middle.
If Severe Enough, May Cause The Development Of TWO Phenotypes
The Random Change
In Allele Frequency
In Small Populations, Individuals That Carry A Particular Allele May Leave More Descendents Than Other Individuals, Just By Chance. Over Time, A Series Of Chance Occurrences Of This Type Can Cause An Allele To Become Common In A Population
The Bottleneck Effect
Under What Conditions Will Evolution NOT Occur:
Five Conditions Are Required To Maintain Genetic Equilibrium From Generation To Generation:
All Members Of The Population Must have An Equal Opportunity To Produce Offspring
Genetic Drift Has Less Effect On Large Populations
New Alleles Must Not Enter
Rare Alleles Must Not Be Allowed To Leave
Mutations Introduce New Alleles Causing A Change In Allele Frequencies
All Genotypes Must Have Equal Opportunity To Survive & Reproduce
No Phenotype Can Have An Advantage Over Another