How Natural Selection and Endosymbiotic Theory relate
Endosymbiosis explains the origin of mitochondria and chloroplasts, but could it also of different species set up symbiotic relationships and formed new organisms. points us to one of the basic processes of evolution: natural selection. Another example of mutual symbiosis is the relationship which exists between the my theory, for such could not have been produced through natural selection.” to the origin of intracellular organelles is the principle of endosymbiosis. He was the first to study and describe the potential endosymbiotic nature in these cells. into a symbiotic relationship with eukaryotic cells through endosymbiosis. through natural selection, became more prevalent than other types of cells.
If it benefited the calves' health in some way, then the allele would be selected for through enhanced survival and reproduction of the calves. A third possibility is that the mutation is neutral, in which case its frequency in the population could be affected by genetic driftor through its being linked to another, beneficial gene.
Farming practices artificial selection may also affect the allele's frequency.
For example, mating is non-random, with much of the dairy herd inseminated artifically using semen from a relatively small number of bulls. If some of these bulls carried the A1 allele, its frequency in the population's gene pool could increase relatively quickly.
So both natural and artifical selection may have led to evolution: Gut symbioses are quite common among herbivorous animals, with symbiotic bacteria, fungi and protozoa providing the enzymes that their host lacks to digest its plant food.
Both host the ruminant and endosymbiont community benefit from this ecological relationship. The host benefits from the microbes' ability to digest a wide variety of plant materials - including cellulose, hemicellulose, and starch - and produce volatile fatty acids and other energy-rich compounds.
The microbes in turn are provided with a warm, moist, anaerobic environment - and a never-ending nutrient supply. A recent study examined the variation in cattle milk protein genes, lactose tolerance in modern humans, and stone-age cattle-farming sites Beja-Pereira et al.
The authors concluded that their data showed evidence of a 'gene-culture evolution between cattle and humans. This lead to the formation of the Endosymbiotic Hypothesis. Wallin published his findings in his work, Symbiogenesis and the Origins of Species, alongside Mereschocowsky, where they formulated their ideas of symbiogenesis. Their theories were originally rejected due the assumption that mitochondria and chloroplasts did not contain DNA.
However, this was proven false during the s, when Hans Ris revived the theory. Lynn Margulis contributed to the endosymbiosis theory with the publication of her work, Symbiosis in Cell Evolution. Her research claimed that the origin of mitochondria were separate organisms that originally entered into a symbiotic relationship with eukaryotic cells through endosymbiosis.
This became the primary support for the endosymbiotic theory, causing her to became the leading figure behind the endosymbiotic hypothesis. Margulis essentially argued against the idea of random mutation, which was accepted as the main source of genetic variation with species.
Instead she thought a symbiotic merger played a much larger role in the creation of new genomes and genetic diversity.
She believed that instead of mutations, DNA in the cytoplasm of cells originated from the genes of prokaryotes bacteria that had become organelles. Lynn Margulis at the University of Massachusetts Amherst. Lynn Margulis continued to study the origins of mitochondira and chloroplast in eukaryotic cells during her time at University of Massachusetts Amherst. She discovered that these organelles originated as prokaryotic endosymbionts that later started to show in eukaryotic cells.
Structural Biochemistry/The Endosymbiotic Theory
Margulis showed convincing research evidence that mitochondria evolved from aerobic bacteria called Proteobacteria, and chloroplasts evolved from endosymbiotic cyanobacteria.
Margulis proposed that eukaryotic flagella and cilia originated from endosymbiotic spirochetes. Due to lack of DNA and the fact that they do not show any ultrastructural similarities to prokaryotes, there is not enough evidence to support this claim.
Even though DNA is not present, peroxisomes are considered to be a consequence from the origin of endosymbiotic. The possibility that peroxisomes may have an endosymbiotic origin has also been considered, although they lack DNA.
Christian de Duve proposed that they may have been the first endosymbionts, allowing cells to withstand growing amounts of free molecular oxygen in the Earth's atmosphere.
Endosymbiosis - The Appearance of the Eukaryotes
However, it now appears that peroxisomes may be formed de novocontradicting the idea that they have a symbiotic origin. According to Keeling and Archibald,  the usual way to distinguish organelles from endosymbionts is by their reduced genome sizes. As an endosymbiont evolves into an organelle, most of their genes are transferred to the host cell genome.
Comparisons with their closest free living cyanobacteria of the genus Synechococcus having a genome size 3 Mb, with genes revealed that chromatophores underwent a drastic genome shrinkage.Endosymbiotic Theory in Plain English
Chromatophores contained genes that were accountable for photosynthesis but were deficient in genes that could carry out other biosynthetic functions; this observation suggests that these endosymbiotic cells are highly dependent on their hosts for their survival and growth mechanisms.
Thus, these chromatophores were found to be non-functional for organelle-specific purposes when compared to mitochondria and plastids. This distinction could have promoted the early evolution of photosynthetic organelles. The loss of genetic autonomy, that is, the loss of many genes from endosymbionts, occurred very early in evolutionary time.
The first fate involves the loss of functionally redundant genes,  in which genes that are already represented in the nucleus are eventually lost. The second fate involves the transfer of genes to the nucleus. Protein coding RNAs in mitochondria are spliced and edited using organelle-specific splice and editing sites. Nuclear copies of some mitochondrial genes, however, do not contain organelle-specific splice sites, suggesting a processed mRNA intermediate.
The cDNA hypothesis has since been revised as edited mitochondrial cDNAs are unlikely to recombine with the nuclear genome and are more likely to recombine with their native mitochondrial genome. If the edited mitochondrial sequence recombines with the mitochondrial genome, mitochondrial splice sites would no longer exist in the mitochondrial genome. Any subsequent nuclear gene transfer would therefore also lack mitochondrial splice sites.
The endosymbiont underwent cell division independently of the host cell, resulting in many "copies" of the endosymbiont within the host cell.