10.3: Gene Pools & Speciation
Mission 1: Are You Deep or Shallow?
Mission Objective. You should be able to...
1. Define "gene pool."
2. Explain the requirements of evolution in terms of allele frequencies.
3. Compare the various forms of reproductive isolation.
4. Explain the process of speciation.
5. Identify examples of directional, stabilizing and disruptive selection.
A gene pool consists of all the genes and their different alleles, present in an interbreeding population. This defines a species as a group of potentially interbreeding populations with a common gene pool that is reproductively isolated from other species (Oxford, 2014).
Gene pools are relatively stable over time. New alleles can be introduced as a result of mutation and old alleles can disappear when the last organism carrying that allele dies. Some alleles prove to be advantageous and are more frequent as a result. Immigrations (coming in) and emigrations (leaving) usually result in a change in allele frequencies. When there is a change in allele frequency, it can be determined that some degree of evolution has taken place (Pearson, 2014). Evolution requires that allele frequency change with time in populations (Oxford, 2014).
Mission Objective. You should be able to...
1. Define "gene pool."
2. Explain the requirements of evolution in terms of allele frequencies.
3. Compare the various forms of reproductive isolation.
4. Explain the process of speciation.
5. Identify examples of directional, stabilizing and disruptive selection.
A gene pool consists of all the genes and their different alleles, present in an interbreeding population. This defines a species as a group of potentially interbreeding populations with a common gene pool that is reproductively isolated from other species (Oxford, 2014).
Gene pools are relatively stable over time. New alleles can be introduced as a result of mutation and old alleles can disappear when the last organism carrying that allele dies. Some alleles prove to be advantageous and are more frequent as a result. Immigrations (coming in) and emigrations (leaving) usually result in a change in allele frequencies. When there is a change in allele frequency, it can be determined that some degree of evolution has taken place (Pearson, 2014). Evolution requires that allele frequency change with time in populations (Oxford, 2014).
Reproductive Isolation of Populations. Members of the same species (same gene pool) can be stopped from reproducing because there is a barrier between them. Barriers can be geographical, temporal, behavioral or related to hybridization infertility. Geographical isolation happens when land/water formations prevent males and females from finding each other, which makes interbreeding impossible. Temporal isolation refers to incompatible time frames that prevent populations or their gametes from encountering one another. Behavioral isolation can occur when one population’s lifestyle and habits are incompatible with those of another population (Oxford, 2014).
Find two examples of each kind of reproductive isolation.
Speciation. Gradualism is one of two theories about the pace of evolutionary change. It was the prevailing idea that species slowly change through a series of intermediate forms. However, there were gaps in the fossil record that did not support this theory. Punctuated equilibrium holds that long periods of relative stability in a species are punctuated by periods of rapid evolution. According to this theory, gaps in the fossil record are not gaps at all, as there was no long sequence of intermediate forms. Events such as geographic isolation and the opening of new niches within a shared geographic range can lead to rapid speciation (Oxford, 2014).
Image courtesy of StPinigigBlog
Find two examples of each kind of reproductive isolation.
Speciation. Gradualism is one of two theories about the pace of evolutionary change. It was the prevailing idea that species slowly change through a series of intermediate forms. However, there were gaps in the fossil record that did not support this theory. Punctuated equilibrium holds that long periods of relative stability in a species are punctuated by periods of rapid evolution. According to this theory, gaps in the fossil record are not gaps at all, as there was no long sequence of intermediate forms. Events such as geographic isolation and the opening of new niches within a shared geographic range can lead to rapid speciation (Oxford, 2014).
Image courtesy of StPinigigBlog
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The image to the left compares gradualism and punctuated equilibrium. Gradualism shows a slow change over geological time. Punctuated equilibrium shows relatively rapid changes over a short period of time followed by periods of stability.
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