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Reproductive isolation

 
Reproductive Isolation

 
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Reproductive isolation
 
 
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An important concept in evolutionary biology, reproductive isolation is a category of mechanisms that prevent two or more populations from exchanging genes. The separation of the gene pool
Gene pool

In population genetics, a gene pool is the complete set of unique alleles in a species or population....
s of populations, under some conditions, can lead to the genesis of distinct species
Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring....
. Reproductive isolation can occur either by preventing fertilization, or by the creation of a degenerate or sterile hybrid, such as the case with the common mule
Mule

In its common modern meaning, a mule is the offspring of a male donkey and a female horse.Mules are classified as an F1 hybrid.The term "mule" was formerly applied to the infertile offspring of any two creatures of different species....
 and the hinny
Hinny

A hinny is a domestication equine hybrid which is the offspring of a male horse and a female donkey . It is similar to the more common mule, but mules are the product of a female horse and a male donkey....
.

According to Ernst Mayr, in his 1942 book, the term was invented by Alfred E.






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An important concept in evolutionary biology, reproductive isolation is a category of mechanisms that prevent two or more populations from exchanging genes. The separation of the gene pool
Gene pool

In population genetics, a gene pool is the complete set of unique alleles in a species or population....
s of populations, under some conditions, can lead to the genesis of distinct species
Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring....
. Reproductive isolation can occur either by preventing fertilization, or by the creation of a degenerate or sterile hybrid, such as the case with the common mule
Mule

In its common modern meaning, a mule is the offspring of a male donkey and a female horse.Mules are classified as an F1 hybrid.The term "mule" was formerly applied to the infertile offspring of any two creatures of different species....
 and the hinny
Hinny

A hinny is a domestication equine hybrid which is the offspring of a male horse and a female donkey . It is similar to the more common mule, but mules are the product of a female horse and a male donkey....
.

According to Ernst Mayr, in his 1942 book, the term was invented by Alfred E. Emerson in 1935. The term was taken over by Theodosius Dobzhansky
Theodosius Dobzhansky

Theodosius Grygorovych Dobzhansky, also known as T. G. Dobzhansky, and sometimes Anglicized to Theodore Dobzhansky was a noted genetics and evolutionary biologist, and a central figure in the field of evolutionary biology for his work in shaping the unifying modern evolutionary synthesis....
 (1937), and then strongly promoted especially by Mayr himself.

Fertilization barriers (pre-zygotic)

Pre-zygotic barriers to fertilization include everything from a physical barriers (such as an ocean) formed between two populations, to ethological (behavioral) differences, to errors in cell division that cause incompatibility between populations.

Speciation
Speciation

Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages....
 by reproductive isolation is frequently seen in plants, with errors in division during mitosis
Mitosis

Mitosis is the process in which a eukaryotic cell separates the chromosomes in its cell nucleus, into two identical sets in two daughter nuclei....
 doubling the number of chromosome
Chromosome

A chromosome is an organized structure of DNA and protein that is found in Cell . A chromosome is a single piece of DNA that contains many genes, regulatory sequence and other genetic sequence....
s and thereby preventing even pairing of chromosomes with normal gamete
Gamete

A gamete is a Cell that fuses with another gamete during fertilization in organisms that sexual reproduction. In species which produce two morphologically distinct types of gametes, and in which each individual produces only one type, a female is any individual which produces the larger type of gamete?called an ovum ?and a male produces th...
s during fertilization. For various species that bloom
Blossom

Blossom is a term given to the flowers of stone fruit fruit tree and of some other plants with a similar appearance that flower profusely but for a short period of time in the spring....
 seasonally, the time of gamete release can prevent hybridization, a temporal isolation. For animal species, mating might be stymied. Incompatible genitalia forms a mechanical reproductive isolation, and members of opposite sexes often fail to recognize one another, due to some morphological difference used to identify a potential mate.

The gametes of different species are frequently incompatible, and do not form a viable zygote
Zygote

A zygote is a cell that is the result of fertilization. That is, two ploidy cells—usually an ovum from a female and a sperm cell from a male—merge into a single ploidy cell called the zygote ....
. Sperm may not possess the proper enzymes for penetrating the coat of the ovum
Ovum

An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization....
, or have the proper chemical markers to signal the egg cell to accept it.

Hybrid barriers (post-zygotic)


If fertilization does occur, several other barriers for the hybrid exist. The first is gametic: the gamete
Gamete

A gamete is a Cell that fuses with another gamete during fertilization in organisms that sexual reproduction. In species which produce two morphologically distinct types of gametes, and in which each individual produces only one type, a female is any individual which produces the larger type of gamete?called an ovum ?and a male produces th...
s successfully combine, but then immediately die before any cell division can occur. The second is zygotic: the zygote
Zygote

A zygote is a cell that is the result of fertilization. That is, two ploidy cells—usually an ovum from a female and a sperm cell from a male—merge into a single ploidy cell called the zygote ....
 forms but quickly dies. The third is embryonic or larval: which is spontaneous abortion of the hybrid fetus
Fetus

A fetus is a developing mammal or other viviparous vertebrate, after the embryonic stage and before childbirth. The plural is fetuses, or sometimes feti....
. The fourth is hybrid inviability: the offspring is born but is unfit
Fitness (biology)

Fitness is a central concept in evolution. It describes the capability of an individual of certain genotype to reproduce, and usually is equal to the proportion of the individual's genes in all the genes of the next generation....
, quickly succumbs to environmental pressures, and dies. The fifth is hybrid sterility: the offspring can produce no offspring of its own, isolating its genes from both parental groups. Finally, hybrids that do produce offspring can, potentially, produce sterile progeny. This is known as F2 breakdown. These mechanisms prevent the recycling of genetic material in distinct species.

Interspersed repeats


Insertion of interspersed repeat
Interspersed repeat

Interspersed repetitive DNA is found in all eukaryotic genomes. These sequences propagate themselves by RNA mediated transposition and they have been called retrotransposons....
s creates non-homologies between otherwise homologous DNA sequences, creating barriers to gene conversion
Gene conversion

Gene conversion is an event in DNA genetic recombination, which occurs at high frequencies during meiosis division but which also occurs in somatic cells....
. This barrier acts as an isolating mechanism protecting nascent novel genes from being overwritten by the progenitors of this gene. This uncoupling allows the evolution of new genes, both within gene families
Gene family

A gene family is a set of genes with a known homology . They are generally biochemically similar. Genes are categorized this way into families, depending on shared nucleotide or protein sequences....
 and also allelic
Allele

An allele is one member of a pair or series of different forms of a gene. Usually alleles are coding region, but sometimes the term is used to refer to a junk DNA....
 forms of a gene. The importance is that this allows the splitting of a gene pool
Gene pool

In population genetics, a gene pool is the complete set of unique alleles in a species or population....
 without requiring physical isolation of the organisms harboring those gene sequences.

See also

  • Assortative mating
    Assortative mating

    Assortative mating takes place when sexual reproduction organisms tend to mating with individuals that are like themselves in some respect or dissimilar ....