Scope, Sequence, and Coordination

A Framework for High School Science Education

Based on the National Science Education Standards

Genetic Variability

The Processes of Evolution: Mutation, Recombination, and Natural Selection
Species evolve over time. Evolution is the consequence of the interactions of (1) the potential for a species to increase its numbers, (2) the genetic variability of offspring due to mutation and recombination of genes, (3) a finite supply of the resources required for life, and (4) the ensuing selection by the environment of those offspring better able to survive and leave offspring.

Further Description:

Darwinian fitness is based upon the natural selection of random chance variations in a gene pool of a population. The selection process allows for "favorable" genetic variations to better compete. Individuals carrying these variations are better able to take advantage of unexplored habitats or may require different biological or physical aspects of their niche. These variations are then inherited through sexual reproduction.

Variations that enable individuals to produce more offspring are considered to be "most fit." These variations become more frequent with each generation. Over time, individuals carrying fit variations can speciate. Speciation occurs when individuals become genetically isolated from other groups by conditions that prevent interbreeding.

Concepts Needed:

Grade 9

Reproduction, variability, adaptation, niche, habitat

Grade 10

Recombination, speciation, mutation, adaptation, selective pressures, adaptive radiation, convergent evolution, divergent evolution, parallel evolution

Grade 11

Variability, common descent, fitness, inheritance, Lamarckism

Grade 12

Gene pool, genetic drift, pre- and post-mating isolating mechanisms, geographic isolation, allele frequency, gene mutations, chromosomal mutations, speciation, gradualism, punctuation

Empirical Laws or Observed Relationships:

Many traits show high heritability, that is, similarity between parents and offspring; this evidence suggests that some variation for that trait is genetically based. Environmental influences on individuals can also produce important variation, but that variation is not observed to be inherited and cannot drive evolution or adaptation. Phenotypic variation equals genetic variation plus environmental variation.

Theories or Models:

Natural selection, modes of speciation, allopatry and sympatry, disruptive selection, stabilizing selection, directional selection, Hardy-Weinberg law, genetic drift, founder effect, heterozygote superiority

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Micro-Unit Description:

Genetic Variability
Students should observe the phenotypic expression of mutations and determine their evolutionary significance in terms of "fitness." They should examine the processes of genetic variability, including mutations, crossing over, and sexual recombination. They can study the genetic basis of evolution by examining artificial breeding experiments.

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