Evolution: Mutations, Natural Selection, Genetic Drift and Speciation
An Overview of Mutations, Natural Selection, Genetic Drift and Speciation
In Evolution: The Basics I gave the basics of evolution including mutations, natural selection and speciation in this I will go into further detail about these as well as go into genetic drift
Mutations
Mutations are random changes in the sequence of the nucleotide base pares (bases for short) of DNA. The bases are adenine (A), thymine (T), guanine (G), and cytosine (C). It is these that code your genes and it is your genes that determines your inherited traits (your hight, skin color, eye color, number of arms, number of legs, etc).
Causes of mutations
Mutations have two causes: damage to DNA and errors in the copying of the DNA when a cell divides. DNA can be damaged by certain forms of radiation (examples: ionizing radiation, ultraviolet radiation) and some chemicals (example: free radicals).
Types of mutations
Point
• A point mutation is a change in a single base. Example: AGTTCG changes to AGTCGC. The fifth nucleotide base changed from a T to a C.
Inversion
• In an inversion mutation a section of the sequence of the bases of DNA is reversed. Example: AGTTCG changes to AGTGCT.
Insertion
• An insertion mutation is the addition of new bases. Example: AGTTCG changes to AGTCDGTCG.
Deletion
• A deletion is the loss of bases from the DNA. Example: AGTTCG changes to ACG.
Frameshift
• Protein coding sections of DNA are divided into codons three bases long. An insertion or deletion mutations can alter the sequence of codons by changing the positions of the bases with in them by one space. Example: AGT TCG CGA changes to AGG TTC GCG or ATT CGC GAC.
Effects of mutations
Mutations can have a wide variety of effects or mutations could do nothing. It depends on where the mutation occurs in the DNA.
If a mutation occurs in a non-coding part of the DNA its not going to do anything. Most of the DNA in the human genome is non-coding. These portions of DNA are sometimes called "junk DNA" but calling them "junk" is a misnomer as much of the non-coding sections of DNA may serve some purpose other than coding genes. Some of the non-coding DNA is inactive genes or endogenous retroviruses (inactive viral DNA injected into the DNA of an individual and passed down to its offspring).
If a mutation occurs in a coding part of the DNA then will alter what the gene codes for. The alteration depends on the gene and the mutation, it could be a drastic change or no change at all. The changes can be ether harmful, beneficial, neutral or silent.
Harmful mutations are mutations a decrease an organisms chances of survival and reproduction, beneficial mutations increase an organisms chances of survival and reproduction. While harmful mutations are more well known then beneficial mutations (increase in cancer risks, being born with out arms or legs, etc) beneficial mutations do occur (bacteria developing resistance to antibiotics (it's beneficial to them), Italian wall lizards left on Pod Mrcaru evolving cecal valves, the evolution of lactose tolerance into adulthood in humans). Some mutations can be beneficial or harmful depending on the environment (example: sickle cell anemia; in places with high chances of catching malaria it is beneficial, in places with low chances of catching malaria it is harmful). Neutral are nether harmful nor beneficial (example: green eyes).
A silent mutation is a mutation in a coding portion of DNA however despite happening in a coding portion of the DNA silent mutations have no effect.
Natural Selection
Natural selection is the process where certain traits are "selected" for while other traits are "weeded out". The "selection" process is a natural unguided process where traits that increase an organisms chances of survival and reproduction with offspring who themselves survive and reproduce build up in a population while traits the decrease an organisms chances of survival and reproduction will decrease in the population.
As said in the mutation section: mutations effect your inherited traits and as said in the effects of mutations section; mutations can be beneficial, harmful or have no effect at all. Natural selection acts on these mutations "selecting" for the beneficial and "weeding out" the harmful mutations. Mutations that don't do anything will build up in a population unaffected by natural selection.
Sexual Selection
In natural selection traits that are beneficial to an organisms survival and reproduction are selected for but in sexual selection only traits that increase chances of reproduction regardless of whether they are beneficial or harmful.
Peacocks have large beautiful feathers that can extend out like a fan. These feathers are used to attract peahens to mate with them. However the feathers requirer allot of energy and slow a peacock down making it easier pray. So why did they evolve them? Because even though the large feathers are a harmful trait, it does attract the peahens thus increasing a peacocks chances of mating and reproduction.
Peacocks are not the only animals with harmful traits that are sexually selected for. Deer antlers have no other purpose than for fighting for mating rights. Male elephant seals have huge bulks that serve no other purpose than fighting for mating rights. Many animals species males and even females will put on displays to attract mates that serve no other purpose than to attract mates.
Genetic drift
While natural selection is an orderly system but not all evolution is so orderly. Natural selection doesn't act on mutations that are nether beneficial or harmful and even if a mutation is beneficial or harmful due to circumstances natural selection may not get a chance to act on them.
If you take a species and split it into two genetically identical populations into two environments exactly the same with the same selective pressures. The two populations will still differentiate genetically due to genetic drift. If the populations remain separate for long enough they will become two different species.
Speciation
A species is a taxonomic rank defined as a group of organists capable of inter breeding and producing fertile offspring. If two animals are incapable of mating and producing fertile offspring they are two different species.
As said above when a single population splits into two populations genetic differences build up in the two populations. Given enough time the two populations will be genetically distinct enough that they will be unable to interbreed and fertile offspring. They two populations would have speciated.
There are for methods of speciation: allopatric, peripatric, parapatric and sympatric.
Mutations
Mutations are random changes in the sequence of the nucleotide base pares (bases for short) of DNA. The bases are adenine (A), thymine (T), guanine (G), and cytosine (C). It is these that code your genes and it is your genes that determines your inherited traits (your hight, skin color, eye color, number of arms, number of legs, etc).
Causes of mutations
Mutations have two causes: damage to DNA and errors in the copying of the DNA when a cell divides. DNA can be damaged by certain forms of radiation (examples: ionizing radiation, ultraviolet radiation) and some chemicals (example: free radicals).
Types of mutations
Point
• A point mutation is a change in a single base. Example: AGTTCG changes to AGTCGC. The fifth nucleotide base changed from a T to a C.
Inversion
• In an inversion mutation a section of the sequence of the bases of DNA is reversed. Example: AGTTCG changes to AGTGCT.
Insertion
• An insertion mutation is the addition of new bases. Example: AGTTCG changes to AGTCDGTCG.
Deletion
• A deletion is the loss of bases from the DNA. Example: AGTTCG changes to ACG.
Frameshift
• Protein coding sections of DNA are divided into codons three bases long. An insertion or deletion mutations can alter the sequence of codons by changing the positions of the bases with in them by one space. Example: AGT TCG CGA changes to AGG TTC GCG or ATT CGC GAC.
Effects of mutations
Mutations can have a wide variety of effects or mutations could do nothing. It depends on where the mutation occurs in the DNA.
If a mutation occurs in a non-coding part of the DNA its not going to do anything. Most of the DNA in the human genome is non-coding. These portions of DNA are sometimes called "junk DNA" but calling them "junk" is a misnomer as much of the non-coding sections of DNA may serve some purpose other than coding genes. Some of the non-coding DNA is inactive genes or endogenous retroviruses (inactive viral DNA injected into the DNA of an individual and passed down to its offspring).
If a mutation occurs in a coding part of the DNA then will alter what the gene codes for. The alteration depends on the gene and the mutation, it could be a drastic change or no change at all. The changes can be ether harmful, beneficial, neutral or silent.
Harmful mutations are mutations a decrease an organisms chances of survival and reproduction, beneficial mutations increase an organisms chances of survival and reproduction. While harmful mutations are more well known then beneficial mutations (increase in cancer risks, being born with out arms or legs, etc) beneficial mutations do occur (bacteria developing resistance to antibiotics (it's beneficial to them), Italian wall lizards left on Pod Mrcaru evolving cecal valves, the evolution of lactose tolerance into adulthood in humans). Some mutations can be beneficial or harmful depending on the environment (example: sickle cell anemia; in places with high chances of catching malaria it is beneficial, in places with low chances of catching malaria it is harmful). Neutral are nether harmful nor beneficial (example: green eyes).
A silent mutation is a mutation in a coding portion of DNA however despite happening in a coding portion of the DNA silent mutations have no effect.
Natural Selection
Natural selection is the process where certain traits are "selected" for while other traits are "weeded out". The "selection" process is a natural unguided process where traits that increase an organisms chances of survival and reproduction with offspring who themselves survive and reproduce build up in a population while traits the decrease an organisms chances of survival and reproduction will decrease in the population.
As said in the mutation section: mutations effect your inherited traits and as said in the effects of mutations section; mutations can be beneficial, harmful or have no effect at all. Natural selection acts on these mutations "selecting" for the beneficial and "weeding out" the harmful mutations. Mutations that don't do anything will build up in a population unaffected by natural selection.
Sexual Selection
In natural selection traits that are beneficial to an organisms survival and reproduction are selected for but in sexual selection only traits that increase chances of reproduction regardless of whether they are beneficial or harmful.
Peacocks have large beautiful feathers that can extend out like a fan. These feathers are used to attract peahens to mate with them. However the feathers requirer allot of energy and slow a peacock down making it easier pray. So why did they evolve them? Because even though the large feathers are a harmful trait, it does attract the peahens thus increasing a peacocks chances of mating and reproduction.
Peacocks are not the only animals with harmful traits that are sexually selected for. Deer antlers have no other purpose than for fighting for mating rights. Male elephant seals have huge bulks that serve no other purpose than fighting for mating rights. Many animals species males and even females will put on displays to attract mates that serve no other purpose than to attract mates.
Genetic drift
While natural selection is an orderly system but not all evolution is so orderly. Natural selection doesn't act on mutations that are nether beneficial or harmful and even if a mutation is beneficial or harmful due to circumstances natural selection may not get a chance to act on them.
If you take a species and split it into two genetically identical populations into two environments exactly the same with the same selective pressures. The two populations will still differentiate genetically due to genetic drift. If the populations remain separate for long enough they will become two different species.
Speciation
A species is a taxonomic rank defined as a group of organists capable of inter breeding and producing fertile offspring. If two animals are incapable of mating and producing fertile offspring they are two different species.
As said above when a single population splits into two populations genetic differences build up in the two populations. Given enough time the two populations will be genetically distinct enough that they will be unable to interbreed and fertile offspring. They two populations would have speciated.
There are for methods of speciation: allopatric, peripatric, parapatric and sympatric.
Allopatric
Allopatric speciation is caused when geologic isolation causes a single population to split into two populations. Through genetic drift the two populations eventually became separate enough genetically that they are separate species.
Peripatric speciation
Peripatric speciation is similar to allopatric speciation in exception to size. In peripatric speciation a small portion of the parent population splits from the parent population. The child population though genetic drift speciates becoming a separate species.
Parapatric speciation
If a population is large enough the gene flow between two sides of the population will be slow enough that the organisms at the two end of the population will be separate enough genetically to be separate species. Even though both species are the same species as the organisms in the middle of the population (they can mate with the organisms in the middle of the population and produce fertile offspring) they are separate species from each other (if two organisms from the two end mated with each other they could not produce fertile offspring)
Sympatric
If organisms in a population find a new niche and mating between the the organisms in the old niche and the organisms in the new niche is rare to non-existent the organisms in the new and old niches are effectively two populations even though they are in the same area. As with other forms of speciation though genetic drift the two populations speciate.
Links and sources
DNA and mutations
Understanding evolution - Genetics - Mutations
What causes DNA mutations?
Genetics 101 - DNA Mutations
Kimball's Biology Pages - Mutations
Natural selection
Evolution 101 - Natural Selection
MNSU - Natural Selection
Evolution 101 - Sexual Selection
Sexual Selection
Sexual Selection in Bowerbirds
Genetic drift Evolution 101 - Genetic Drift
Other Sources of Genetic Variation
Genetic Drift and Gene Flow
Speciation
Evolution 101 - Speciation
The Process of Speciation
Published by Lone Wolf
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