Biology D2 – Flashcards

Allele frequency- the percentage with which a specific allele is found in a population. Gene Pool- the sum total of all alleles present in all populations of a particular species.

evolution involved a change in allele frequency in a population's gene pool over a number of generations.

New Species- result from the accumulation of many advantageous alleles in the gene pool of a population over a long period of time. In other words, new species result from Macroevolution. Macroevolution- the accumulation of multiple microevolutionary steps, combined with reproductive isolation. An example would be Darwin's finches.

1) Geographical isolation- occurs when a population is physically separated, usually due to a natural disaster such as an avalanche, fire, earthquake, etc. 2) Temporal isolation- due to timed barriers, e.g. reproducing during different seasons. 3) Behavioral isolation- courtship mating displays may only be recognized by members of the same species, e.g. bird songs.

Polyploidy occurs when more than two sets of homologous chromosomes are present. Examples such as triploidy (3x) and tetraploidy (4x) are often due to a disruption in the meiotic sequence. Chromosomes replicate, but remain together in the same cell. Once polyploidy occurs, the individual is often unable to mate with the original species, causing immediate species divergence.

Speciation- the formation of a new species by splitting of an existing species. Sympatric speciation- occurs in the same geographical area. Allopatric speciation- occurs in different geographical areas.

As populations drift or expand to different geographical locales, local environmental conditions will favor some traits over others, causing phenotypes in different areas to diverge. This can result in radiant speciation. A classic example are the Galapagos Islands, which Darwin first studied.

Convergent Evolution- individuals of different species develop similar traits in response to living in the same habitat. For example, many species of desert plants develop thick cuticles to deter water loss. Divergent Evolution- occurs when different traits share a common evolutionary origin. For example, vertebrate limbs have many unique shapes, but their bone patterns trace back to a common ancestral configuration.

Gradualism - the slow change from one form to another. Punctuated equilibrium- long periods of no change and short periods of rapid evolution. Some causes are volcanic eruptions and meteor impacts on Earth.

Transient polymorphism- Before the industrial revolution, the peppered moths with lighter phenotypes were more common because they blended in with the light colored tree-trunks they rested on. With factories came soot, which darkened the tree barks. In the span of several decades, the predominant phenotype was a much darker grey

Sickle cell anemia is a homozygous recessive disorder (ss). The heterozygous individual (Ss) does not have sickle cell anemia, but is more resistant to malaria than an individual who does not carry a sickle cell gene at all (SS). This creates selective pressure to keep the sickle cell gene in the gene pool, resulting in balanced polymorphism