Concept 23.1: Genetic variation makes evolution possible

Flashcards from Concept 23.1 of Pearson's Campbell Biology, Twelfth Edition.

Natural selection

Force in nature that allows populations of animals to adapt to their environment through genetic components

• Seen with ground finches in the Galapagos Islands evolving to have larger beaks in response to a small seed shortage

  • This led to an increase in average beak depth

Microevolution

The change in allele frequencies in a population over generations, caused by:

• Natural selection (environmental adaptations)

• Genetic drift (chance events)

• Gene flow (population allele transfers)

Genetic variation

The differences in genes or DNA sequences among individuals; this is a prerequisite for evolution by natural selection

• The discovery of this was aided by Gregor Mendel's work on pea plant heritability

• It can be quantified by the percentage of heterozygous loci in a population or the nucleotide sequences of individuals

Gregor Mendel

Scientist that discovered evidence of discrete heritable units (genes) in pea plants

Phenotype

How the trait is expressed in the real world, affected by the inherited genotype and environmental influences

• Though most of these are expressed as two traits, a gradient of traits may appear when determined by two or more genes

  • Seen in horse coat colors or height in humans

Introns

Noncoding DNA segments where most nucleotide differences occur, resulting in no change

Exons

Coding DNA segments where fewer nucleotide differences occur

• Even if DNA is changed here, it rarely results in a change to the amino acid sequence of an encoded protein

Genetic variation sources

Includes:

• Mutation

• Gene duplication

• Other processes

These are accelerated through organisms with short generation times or reproduction through the combination of existing alleles

Mutation

A change in the nucleotide sequence of DNA as a source of genetic variation

• Replication errors, radiation, or chemicals are common sources of this — overall, though, these are rare

• Even a single change can result in a significant phenotypical impact, often becoming at least slightly harmful if not hidden as a recessive trait

• If an organism can produce gametes, these can be passed to offspring

Heterozygote protection

The maintenance of a pool of alleles that could be beneficial with environmental changes through heterozygous individuals

Point mutation

A mutation of a single nucleotide

Neutral variation

A variation with no selective advantage or disadvantage as a result of a point mutation

• Occurs due to genetic redundancy

Gene duplication

The duplication of small segments of DNA, is a key source of genetic variation

• This can result in the accumulation of mutations and new functions, such as mammals' heightened sense of smell

Virus

An infectious agent with rapid mutation rates and short generation times, increasing drug resistance and survival rates