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EVOLUTION AND SPECIATION

UNIT ONE

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MICROEVOLUTION

INTRODUCTION TO EVOLUTION

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MICROEVOLUTION

Individuals of all natural populations share a common gene pool but differ in the alleles they each inherit

As a result of the variations in genotype, they show variations in the phenotype

Individuals do not evolve; populations do

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MICROEVOLUTION

This evolution occurs as a result of a change in the alleles of that population’s gene pool

Over the generations, any allele may increase in frequency OR it may become rare or even lost

Microevolution refers to changes in allele frequencies as an out come of:

a) Mutationb) Natural selectionc) Genetic driftd) Gene flow

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GENETIC STRUCTURE OF POPULATIONS

INTRODUCTION TO EVOLUTION

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GENETIC STRUCTURE OF POPULATIONS

Population geneticists study heredity in groups of individuals called a population

Populations of the same species (ex: pigeons) share morphological (morpho – form) traits:

a. 2 feathered wingsb. 3 toes forward, 1 toe backPopulations also share physiological traits

like homeostatic mechanisms that help the body function in it’s environment

They also respond the same way to basic stimuli – behavioral traits

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GENETIC STRUCTURE OF POPULATIONS

The individuals of each population show variations in the details of the traits they share with the other members (i.e.: color/patterning of feathers on pigeon wings)

Almost every trait of any species may vary, but the variety is far more pronounced in sexually reproducing species

Looking at our definition of a population, this variety is the result of the combining and recombining of the genes of two parents to create offspring

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Qualitative Differences Quantitative Differences

2 or more distinct forms (morphs)

Dimorphism – persistence of 2 forms of a trait in a population

Polymorphism – 3 or more forms of the trait

Range of incrementally small variations in each morph

Typically unique to specific populations

GENETIC STRUCTURE OF POPULATIONS

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EVIDENCES OF EVOLUTION

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FOSSILS

1. Mold fossils2. Cast fossils3. Permineralization (petrification)4. Replacement fossils5. Organic matter (teeth, bones)6. Preservation

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COMPARATIVE ANATOMY

Comparative Morphology – study of body forms and structures of major groups of organisms

Homologous structures – body parts that are structurally similar but different in function; genes for constructing these parts indicates shared ancestry

Analogous structures – structures that serve similar functions but have different origins on embryonic forms

Vestigial structures – have no apparent function in specific organism

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COMPARATIVE EMBRYOLOGY

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BIOGEOGRAPHY

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COMPARATIVE BIOCHEMISTRY

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FOSSIL DATING

Relative Dating – dating fossils relative to their location in rock layers and to each other (estimate only)

Absolute Dating - determination of actual age of fossil

1. Radioactive dating: use of specific radioactive isotopes

2. Amino acid racemization: ratio of left-handed amino acids (living) to right-handed (dead)