species- a group of individuals that look similar and whose members are capable of producing fertile...
TRANSCRIPT
SPECIES-
• A group of individuals that look similar and whose members are capable of producing fertile offspring.
The definition of species derived from two different “concepts”…
1) Morphological Species Concept:
• Based on internal and external similarities and differences.
• MORPHOLOGY
2) Biological Species Concept;• Classification based on an organisms ability to reproduce and produce fertile offspring.
The offspring of two morphologically dissimilar organisms
HYBRID:
• Within a population, individuals vary in many observable traits
• These can be presented on a BELL CURVE.
What causes variations within species…
1) Environmental factors2) Heredity • mutations• genetic recombination• crossing over
Allele Frequency and Genetic Equilibrium
A population is a collection of genes
GENE POOL- • A collection of genes for all the
traits of a population.
ALLELE FREQUENCY- • The % of a specific allele
of a certain gene in the gene pool
GENETIC EQUILIBRIUM-• A population in which allele
frequency does not change.
The Hardy-Weinberg Principle
Weinberg: German physicianHardy: British mathematician
* Observed that allele frequencies in populations remain relatively the same unless acted on by outside influences
Assumptions for Equilibrium:
1. No mutations occur
2. Individuals neither enter nor leave through migration
3. The population is large (ideally infinitely large)
4. Individuals mate randomly
5. Natural selection doesn’t occur
p2 + 2pq + q2 = 1.0 DEMO PROBLEMS:
Disruption of Genetic Equilibrium
A. Mutations-• Physical change of genes or
chromosomes• Produce totally new alleles for
a trait• Can change the frequency of
alleles
B. Migration-
immigration:• movement into a populationemigration: • movement out of a population*Gene flow- The movement of genes into or
out of a population through migration.
Genetic Drift-• Significant only in small and
medium sized populations• An allele may disappear
completely in a small population• More stable in larger
populations
D. Non-Random Mating• Random mating is a requirement
for genetic equilibrium• Many species DO NOT follow
random mating.• Mating is influenced by a variety of
factors…
Reasons for Non-Random Mating:
• Geographic proximity• Selection based on similar physical
characteristics• ASSORTIVE MATING
PROBLEMS FROM NON-RANDOM MATING:
• Mating may amplify certain recessive disorders.
“Survival of the fittest”
• Some members of a population are more likely to contribute genes
E. Natural Selection-
1. Stabilizing Selection-
• Natural selection in which individuals with the average form of a trait have the advantage.
• Natural selection in which individuals with one of the extreme forms of a trait has an advantage.
2. Directional Selection
3. Disruptive Selection• Type of natural
selection in which individuals with either of extreme forms of a trait have advantage.
2. Reproductive Isolation-• Inability of former interbreeding
organism to produce offspring
Prezygotic Isolation:• Obstacle occurs before fertilizationExamples:• Incompatible behavior
• Different mating calls• Different mating seasons
Postzygotic Isolation:• Obstacle occurs after fertilization
Examples:• Offspring may not develop
completely• Offspring may die early• Offspring may not be fertile
RATES OF SPECIATION2 major theories regarding the rate of
speciation:Gradualism:• The idea that divergence of species
occurs smoothly and gradually over time
PUNCTUATED EQUALIBRIUM-
The idea that things live in Genetic Equilibrium then changed in short spurts of time.
• Unicellular organisms may evolve in months or even day
• Other evidence suggests within thousands of years
EXTINCTION:• The point at which
no organisms of a particular species are available to reproduce
• change• Disruption of
habitat