Chpt 23 MasteringBio Pretest

Rabbit ear size tends to decrease as latitude increases. This is an example of _____.

a cline – A cline is a gradual change in a trait along a geographic axis.

According to the Hardy-Weinberg theorem, the frequencies of alleles in a population will remain constant if _____ is the only process that affects the gene pool.

sexual reproduction – Sexual reproduction does not change the frequency of alleles in the gene pool.

The evolutionary effects of genetic drift are greatest when _____.

the population size is small – Changes in the gene pool of a small population are frequently due to genetic drift.

What situation most likely explains the occasional high frequency of certain inherited disorders among human populations established by a small population?

founder effect – The founder effect is genetic drift attributable to colonization by a limited number of individuals from a parent population.

In evolutionary terms, an organism’s fitness is measured by its _____.

contribution to the gene pool of the next generation – Those organisms with adaptations best suited to the current environment will make the most significant contribution to the next generation.

Blue poppies native to China were grown at a plant-breeding center in California. The plants with the thickest leaves were most likely to survive and reproduce in the drier climate. After several generations, the percentage of thick-leaved plants had increased by 42%. This adaptation of the poppies to their new environment is due to _____.

– directional selection The characteristics of the poppies shifted in response to the changed environment.

What is the only evolutionary mechanism that consistently leads to adaptive evolution?

natural selection – Because natural selection has a "sorting" effect, it consistently increases the frequency of alleles that improve the match between an organism and its environment.

How does diploidy help to preserve genetic variation?

It allows recessive alleles that may not be favored in the current environment to be preserved in the gene pool by propagation in heterozygotes. – Natural selection tends to decrease genetic variation. Recessive alleles are shielded from natural selection in heterozygotes.

The original source of all genetic variation is _____.

mutation Mutation is, in itself, very important to evolution because it is the original source of the genetic variation that serves as the raw material for evolution.