EVOLUTION …via Natural Selection. Organisms produce more offspring than can survive.

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Presentation transcript:

EVOLUTION …via Natural Selection

Organisms produce more offspring than can survive.

The environment is hostile and contains limited resources.

Organisms differ in the traits they have.

Some inherited traits provide organisms with an advantage.

Each generation contains proportionately more organisms with advantageous traits.

Evolution: A change in the genetic characteristics of a population from one generation to the next.

Natural Selection: The unequal survival and reproduction that results from the presence or absence of certain traits.

Adaptation: An inherited trait that increases an organism’s chance of survival and reproduction in a certain environment.

Evolution of Populations: Genes & Variation Darwin didn’t know: How traits are passed from one generation to the next. How variations in traits happen.

Mendel + Darwin = Understanding! GENES control inherited traits. Changes in genes cause variation in traits.

Populations Interbreed! GENE POOL: all the genes (and alleles) present in a population.

Relative Frequency: …the number of times an allele occurs in the gene pool, compared to the number of times other alleles for the same gene occur. Expressed as a %.

What is the relative frequency of the allele? (17) (13) 17 ÷ 30 = 57%

In genetic terms, EVOLUTION IS: Any change in the relative frequency of alleles in a population.

Sources of Genetic Variation: Mutations Any change in DNA sequence. Some mutations result in different phenotypes. Changes in phenotype may affect an organism’s fitness (ability to survive/reproduce.) Gene Shuffling Occurs in sexual reproduction. In humans: Independent assortment of homologous chromosomes during gamete formation can result in 8.4 million different genetic combinations. Crossing over. HOWEVER: sexual reproduction will not change a population’s allele frequency.

Single Gene & Polygenic Traits (the number of phenotypes produced for a given trait depends on how many genes control the trait.) Single Gene: ⁰ One gene, two alleles. ⁰ Example: widow’s peak…you either have it or you don’t. Polygenic: ⁰ Controlled by 2 or more genes. ⁰ Example: human height. ⁰ Bell curve.