Biological Evolution.

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Presentation transcript:

Biological Evolution

What is Evolution Evolution is descent with modification Microevolution = changes in gene (allele) frequency in a population from one generation to the next Macroevolution = descent of different species from a common ancestor over many generations

Evolution Explained NOT simply change over time Ex: Life cycle is NOT evolution MUST involve DESCENT through GENETIC INHERITANCE Change in a POPULATION over GENERATIONS of time Underlying Concepts: All organisms share a Common Ancestor Occurs through Natural Selection

Natural Selection Variation in traits: more than one allele for a trait; one allele may be more advantageous than another Differential reproduction: NOT all individuals get to reproduce to their full potential Heredity: adaptations are genetic End result: more advantageous trait allows individuals to survive and produce more offspring

Natural Selection

Natural Selection

Natural Selection

Shift in Allele Frequency Mutations can produce new phenotypes that may or may not be beneficial to the organism If the new allele is beneficial, then those organisms will be more “fit” and therefore better able to reproduce. Over generations of time, this will cause the new allele to become more frequent in the population.

Stabilizing Selection Favors Intermediate phenotypes & eliminates BOTH Extremes Reduces variation and maintains the current average Ex = human birth weight

Directional Selection Favors ONE Extreme & eliminates other phenotypes Most common during times of environmental change or when moving to new habitats. Ex: speed; faster is better so a population will tend to get faster over time.

Favors BOTH Extremes & eliminates Intermediates Disruptive Selection Favors BOTH Extremes & eliminates Intermediates Occurs when environmental change favors an extreme phenotype; not as common. Ex: Prey with distinctive markings; predation causes drift away from the “normal” phenotype in extreme directions.

Fitness Fitness = how good a particular genotype is at leaving offspring in the next generation compared to other genotypes FITNESS is INHERITED! Fitness will increase one or more of the following: Ability to Survive Find a Mate Produce Offspring Fitness is NOT necessarily strongest, fastest, or biggest. Ultimate Goal = transmit GENES to the next generation

Beak Lab Explanation Varied food sources allowed many different beak structures to be beneficial; therefore allowing many phenotypes to reproduce When food source was changed, only beaks with specific phenotypes (ADAPTATIONS) were able to get enough food to survive/reproduce. Over generations of time, the non-beneficial phenotypes would die out and the beneficial phenotypes would become amplified.

Sexual Selection Special case of natural selection Acts on an organism’s ability to obtain &/or successfully copulate with a mate Organisms may go to extreme lengths for sex Peacock tail Elephant seals fight Fruit flies dance Some even die for it! (male praying mantis)

Artificial Selection Artificial Selection = people (NOT nature) select which organisms get to reproduce Farmers and breeders commonly cultivate crops using Selective Breeding

Adaptation Adaptation = inherited characteristic in a population that increases fitness Adaptation Types Behavioral Biochemical Anatomical An adaptation is NOT ACQUIRED during an organism’s lifetime

Lamarck = Acquired Traits (wrong) Giraffes needed longer necks so they “grew” longer necks through repeated use. THIS IS INCORRECT! Giraffes that INHERITED longer necks were better able to survive, so they passed those genes on to their offspring. Darwin = Inherited Variation & Natural Selection (correct)

Adaptation Functional = Produced by Natural Selection Heritable = MUST be able to be INHERITED (genetic trait) Adaptive = increases the fitness of an organism

Speciation Species is the biggest “gene pool” possible under natural conditions. If the organisms can breed and produce fertile offspring, they are the same species. German Sheppard + Chihuahua = puppy (fertile) Horse + Donkey = Mule (sterile hybrid) Horse & Donkey (NOT the same species) Speciation produces 2 or more separate species caused by: Geographic Isolation Reproductive Isolation

Speciation of Fruit Flies

A population of wild fruit flies lays eggs on rotting bananas…

Disaster strikes: a hurricane washes the bananas and immature fruit flies out to sea. The bananas eventually wash up on the mainland. There are now 2 separate populations of fruit flies that cannot mate due to location.

Populations become different due to slightly different conditions on the island. This causes a shift in allele frequency in the island population because of selection pressures.

So we meet again: If another storm reintroduces the island fruit flies to the mainland fruit flies, they will not readily mate with each other due to differing courtship behaviors. The few that do mate produce inviable eggs because of genetic differences in the populations.

EVOLUTION DOES NOT WORK THIS WAY!!! Misconceptions What I NEED is a GOOD FUR COAT! Natural Selection does NOT produce perfection. An organism cannot “adapt” during its lifetime. It cannot “try” to change. That is NOT adaptation. Adaptations MUST be GENETIC! Natural Selection is NOT random: variations that aid survival and reproduction are more likely to become common in the population EVOLUTION DOES NOT WORK THIS WAY!!!

Why aren’t all harmful mutations eliminated from the population through Natural Selection? Sickle Cell Anemia 1 wrong nucleotide base (mutation) 1 different amino acid that changes the shape of the hemoglobin protein Autosomal Recessive Heterozygotes have resistance to Malaria