Evolution
7. The frequency of an allele in a gene pool of a population depends on many factors
and may be stable or unstable over time.
As a basis for understanding this concept:

a. Students know why natural selection acts on the phenotype rather than the genotype of an organism.
b. Students know why alleles that are lethal in a homozygous individual may be
carried in a heterozygote and thus maintained in a gene pool.
c. Students know new mutations are constantly being generated in a gene pool.
d. Students know variation within a species increases the likelihood that at least
some members of a species will survive under changed environmental conditions.


GRADES NINE THROUGH TWELVE—BIOLOGY/LIFE SCIENCES
e. Students know the conditions for Hardy-Weinberg equilibrium in a population
and why these conditions are not likely to appear in nature.
f. Students know how to solve the Hardy-Weinberg equation to predict the fre­
quency of genotypes in a population, given the frequency of phenotypes.


8. Evolution is the result of genetic changes that occur in constantly changing environments. As a basis for understanding this concept:

a. Students know how natural selection determines the differential survival of
groups of organisms.
b. Students know a great diversity of species increases the chance that at least some organisms survive major changes in the environment.
c. Students know the effects of genetic drift on the diversity of organisms in a population.
d. Students know reproductive or geographic isolation affects speciation.
e. Students know how to analyze fossil evidence with regard to biological diversity, episodic speciation, and mass extinction.
f. Students know how to use comparative embryology, DNA or protein sequence
comparisons, and other independent sources of data to create a branching dia­
gram (cladogram) that shows probable evolutionary relationships.
g. Students know how several independent molecular clocks, calibrated against each other and combined with evidence from the fossil record, can help to estimate
how long ago various groups of organisms diverged evolutionarily from one
another.