Microevolution: Definition, Examples,

 

 MICROEVOLUTION

 

1: DEFINITION :-

                Microevolution is the change in allele frequencies that occur over time within a population .

                  These are small changes .

2: Explanation :-

                   Evolution at this scale can be observed over short period of time e.g in generation and the next, the frequency of a gene for a pesticide resistance in a population of crop pests increases , such change might occur because natural selection favored gene .

The change happens relatively short amount of time.

 

·         POPULATION GENETICS :

                   Population genetics is the branch of biology that provides the mathematical structure for the study of the process of microevolution .

 

·         ECOLOGICAL GENETICS :

                   Ecological genetics concerns itself with observing microevolution in the wild .

 

EXAMPLES :

            

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·         The change is due to  four different processes :

1 : MUTATION

2 : SELECTION

3 : GENETIC DRIFT

4 : GENE FLOW

 

 

 

·        MUTATIONS :-

              Mutation are  changes in the DNA sequences of a cells genome and are caused by radiations, viruses & mutagenic chemicals , as well as errors that occur during meiosis or DNA replication .

Mutations can affect the phenotype of an organisms , especially if they occur within the protein coding sequences of a gene .

Errors rates are usually very low –1 in every 10—100 millions bases due to the proofreading ability of DNA polymerases .

 

MUTAGENIC CHEMICALS promote errors in DNA replication , often by interfering with the structure of base pairing .

 

UV RADIATION  induces mutation by causing damage to the DNA structure .

 

CHROMOSOMAL CROSS OVER  in some organisms used to exchange DNA and recombine genes errors in alignment during meiosis can also cause mutations. These errors create large structural changes in DNA sequences – duplication , inversion or deletion , of entire region ,or the accidental exchanging whole parts of different chromosomes .

 

 

VIRUSES  that use RNA as their genetic material have rapid mutation rates , which can be an advantages since these viruses will evolve constantly and rapidly , and thus evade the human immune system .      

 

 

EXAMPLES :-

 

 

                                                    

                                          

     

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·        SELECTION :- 

Selection is the process by which heritable traits that make it more likely for an organisms to survive and successfully reproduce become more common in a population over successive generations .

 

Two types of selection :

1 :- NATURAL SELECTION :

2 :- ARTIFICIAL SELECTION :

 

      1 :- NATURAL SELECTION :

                                                Natural selection genetic variation within a population of organisms means that some individuals will survive more successfully than others in their current environment .

Natural selection acts on the phenotype or the observable characteristics of an organisms , but genetic basis of any phenotype which gives a reproductive advantages will become more common in a population .

Over time this become adaptation and may eventually results in the  speciation (the emergences of new species )

 2 :- ARTIFICIAL SELECTION :

                                                A process by which animals and plants with traits considered desirable by human breeders are systematically favored for reproduction .

 

EXAMPLES :-

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·        GENETIC DRIFT :

 

Ø  Genetic drift is the change in the relative frequency in which gene variant occur in a population due to random sampling .

Ø  Alleles in the offspring in the population are a random sample of those in the parents and a chance has a role in determining whether a given individuals survive and reproduces .

Ø  A population’s ALLELE FREQUENCY is the fraction or percentage of its gene copies compared to the total number of gene alleles that share a particular form .

Ø  Genetic drift is an evolutionary process which leads to change in allele frequencies over time .

Ø  The effect of genetic drift is larger in  small population , and smaller in larger population .

Ø  In 1968 MOTOO KIMURA rekindled the debate with his “NEUTRAL THEORY OF MOLECULAR EVOLUTION “ which  claims that most of the changes in the genetic material are caused by genetic drift . 

EXAMPLES :-

                        

 

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·         GENE FLOW :-

 

Ø  Gene flow is the exchange of gene between populations , which are usually of the sam e species .

Ø  Examples of Gene flow within a species include the MIGRATION an the BREEDING OF ORGANISMS or the exchange of POLLEN .

Ø  MIGRATION into or out of a population can change allele frequency as well as introducing genetic variation into a population .

Ø  IMMIGRATION may add new genetic material to the established gene pool of a population .

Ø  Conversely EMIGRATION  may remove genetic material .

Ø  GENE FLOW is hindered by mountains ranges ,oceans and deserts or even Man made structures such as “THE GREAT WALL OF CHINA “  which has hindered the flow of plant genes .

Ø  Depending on how far two species have diverged since their “most recent common ancestors “ it may still be possible for them to produce off springs as with donkeys and horses mating produces mules .

Ø  Viable hybrid form and this new species have intermediate characteristics or possess a totally new phenotype .

Ø  HORIZONTAL GENE TRANSFER is the transfer of genetic material form one organisms to another organisms that is not its offspring ; this is most common among bacteria (In medicine , the contributes to the spread of antibiotic resistance , as when one bacteria acquires resistance genes it can rapidly transfer them to other species .

 

EXAMPLES :-

 

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