10.3 Flashcards
Speciation Description
Among evolutionary biologists there is some discussion as to the rate at which species evolve.
Speciation is how a new kind of plant or animal species is created. Speciation occurs when a group within a species separates from other members of its species and develops its own unique characteristics.
The creation of a new species is due to selection, mutation or isolation, polyploidy. They have changed enough to become a new species. This change could be gradual or rapid.
Hardy-Weinberg Analysis & Allele Frequencies
In order to calculate the frequencies of alleles, genotypes or phenotypes within a population- the Hardy Weinberg equation is used. This is different from finding phenotypic ratios.
Reference worksheet and know equations and how to solve these problems.
p = frequency of the dominant allele (allele T in the example below)
q = frequency of the recessive allele (allele t in the example below)
▪When looked at individually, the frequencies of the alleles on chromosomes must add up to 1.
Geographic isolation
Happens when physical barriers such as land or water formations prevent males and females from interbreeding. For example, a river, a mountain, or a clearing in a forest could separate populations. Tree snails in Hawaii: one population lives on one side of a volcano and another population lives on the other side.
Temporal Isolation
Refers to incompatible time frames that prevent populations or their gametes from encountering each other. For example, if the female parts of the flowers of one population of plants reach maturity at a different time compared with the release of pollen of another population, the two will have great difficulty producing offspring together.
Behavioral Isolation
Can happen when one population’s lifestyle and habits are not compatible with those of another population. For example, many species of birds rely on courtship display in order for one sex to mate with the other. If the males of one population have a version of a courtship display that is significantly different from another population, the females may not find the males of the other population as a potential mate.
Directional Selection
When a phenotype is favored over another by natural selection
Example: When the lighter-colored peppered moth’s frequency in the population decreased during the industrial revolution, while the darker phenotype increased in the population.
Stabilizing selection
When one phenotype is favored over two extreme phenotypes
Example: A flowering plant might make some flowers with more nectar and some flowers with less nectar, but because producing excessive nectar would be a drain on the plant’s sugar resources and producing too small a quantity would discourage insects from returning, an intermediate quantity is produced that is a balance between too much and too little.
Disruptive
When two extreme phenotypes are favored by natural selection, rather than one intermediate phenotype.
Example: Tadpoles of spadefoot toads in the Americas have two possible morphologies, one for omnivorous diet and one for a strictly carnivorous diet that includes cannibalism if food sources are scarce.
Polyploidy
Haploid cells such as sex cells contain one set of chromosomes (n), Diploid cells such as somatic cells, contrain two sets of chromosomes (2n), Polyploidy refers to the situation in which a cell contains three or more sets of chromosomes.
Such a situation can arise when cell divisions do not completely separate the copies of chromosomes into distinct nuclei and they end up in the same cell (non-disjunction).
Polyploidy is more common in plants than animals. Having an extra set of chromosomes has the consequence of making errors in replication more common- if one population evolves at a different rate from another, the two could become so dissimilar they no longer belong to the same species.
If this takes place, speciation can occur after one generation
Gradualism vs. Punctuated Equilibrium
changes are small, continuous and slow ( gradualism )
Supporters of this view argue that the fossil records show a succession of small changes in the phenotypes of species, indicating that the process of speciation is a steady, ongoing one, with transitional stages between major changes in a phylogenetic line.
The changes are relatively quick and followed by long periods of little or no change (punctuated equilibrium).
Supporters of this view argue that speciation happens quickly, often in response to a change in the environment, for example, after a volcanic eruption, a meteorite impact or a major climate change.
