GENE POOLS AND SPECIATION HL
Nature of science:
Looking for patterns, trends and discrepancies—patterns of chromosome number in some genera can be explained by speciation due to polyploidy. (3.1)
Understandings:
• A gene pool consists of all the genes and their different alleles, present in an interbreeding population.
• Evolution requires that allele frequencies change with time in populations.
• Reproductive isolation of populations can be temporal, behavioural or geographic.
• Speciation due to divergence of isolated populations can be gradual.
• Speciation can occur abruptly.
Interbreeding populations
The gene pool is all genetic information present in the reproducing members of a population at a given time. The gene pool can be thought of as a reservoir of genes from which the population can get all its various traits. A large gene pool exists in a population tht shows substantial variety of traits, whereas a small gene pool exists in population whose members show little variation in interbreeding.
Allele frequency is a measure of the proportion of a specific variation of a gene in a population. The allele frequency is expressed as a proportion or a percentage.
Evolution and allele frequencies
Gene pools are generally relatively stable over time. But not always. New alleles can be introduced as a result of mutation and old alleles can disappear when the last organism carrying the allele dies. One result of evolution is that after many generations of natural selection some alleles prove to be advantageous and tend to be more frequent.
Conversely, some alleles are disadvantageous to the survival of the organism in the population and are not passed on. In addition if a population mix as a result of immigrations there will probably be a change in allele frequencies. The same is true in emigrations, when one group with a particular allele leaves the population the gene pool is modified.
Conversely, some alleles are disadvantageous to the survival of the organism in the population and are not passed on. In addition if a population mix as a result of immigrations there will probably be a change in allele frequencies. The same is true in emigrations, when one group with a particular allele leaves the population the gene pool is modified.
Reproductive isolation of populations
In some situations populations of members of the same species can be stopped from reproducing together because there is an insurmountable barrier between them, such a barrier can be geographical, temporal, behavioural, or infertility.
Speciation due to divergence of isolated population
Generally it is agreed that evolution doesn’t happen overnight, but there are 2 main views
-The changes are small, continuous and slow
-The changed are relatively quick and followed by long periods of little or no change.
Speciation due to divergence of isolated population
Generally it is agreed that evolution doesn’t happen overnight, but there are 2 main views
-The changes are small, continuous and slow
-The changed are relatively quick and followed by long periods of little or no change.
Directional, stabilizing, and disruptive selection.
When a phenotype is favoured over another by natural selection, it is called directional selection. In such case, the frequency of one phenotype is seen to increase over time, whereas the other phenotype decreases. This can occur when an organisms environment changes. We have seen how industrial melanism changed the color of the peppered moths.
When a phenotype is favored over two extreme phenotypes it is called stabilizing selection.
When two extreme phenotypes are favoured by natural selection, rather than one intermediate phenotype it is called disruptive selection. Sometimes it is an advantage to have 2 opposing varieties of a phenotype rather than one.
When a phenotype is favored over two extreme phenotypes it is called stabilizing selection.
When two extreme phenotypes are favoured by natural selection, rather than one intermediate phenotype it is called disruptive selection. Sometimes it is an advantage to have 2 opposing varieties of a phenotype rather than one.
polyploidy
Application and skills
• Application: Identifying examples of directional, stabilizing and disruptive selection.
• Application: Speciation in the genus Allium by polyploidy.
• Skill: Comparison of allele frequencies of geographically isolated populations.
Theory of knowledge:
•Punctuated equilibrium was long considered an alternative theory of evolution and a challenge to the long established paradigm of Darwinian gradualism. How do paradigm shifts proceed in science and what factors are involved in their success?
• Application: Identifying examples of directional, stabilizing and disruptive selection.
• Application: Speciation in the genus Allium by polyploidy.
• Skill: Comparison of allele frequencies of geographically isolated populations.
Theory of knowledge:
•Punctuated equilibrium was long considered an alternative theory of evolution and a challenge to the long established paradigm of Darwinian gradualism. How do paradigm shifts proceed in science and what factors are involved in their success?