Examples of descent with modification in the following topics:
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- Darwin dedicated a large portion of his book, On the Origin of Species, to identifying patterns in nature that were consistent with evolution.
- For example, species of unrelated animals, such as the arctic fox and ptarmigan living in the arctic region, have been selected for seasonal white phenotypes during winter to blend with the snow and ice .
- The geographic distribution of organisms on the planet follows patterns that are best explained by evolution in conjunction with the movement of tectonic plates over geological time.
- Like anatomical structures, the structures of the molecules of life reflect descent with modification.
- This is exactly the pattern that would be expected from descent and diversification from a common ancestor.
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- The birds have inherited variation in the bill shape with some birds having wide deep bills and others having thinner bills.
- For example, the ground finches inhabiting the Galápagos Islands comprised several species with a unique beak shape .
- These tortoises were "selected" because they could reach more leaves and access more food than those with short necks.
- Third, Darwin and Wallace reasoned that offspring with the inherited characteristics that allow them to best compete for limited resources will survive and have more offspring than those individuals with variations that are less able to compete.
- This will lead to change in populations over successive generations in a process that Darwin called descent with modification.
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- On the Galapagos Islands, Darwin observed several species of finches with unique beak shapes.
- Out of these three principles, Darwin reasoned that offspring with inherited characteristics that allow them to best compete for limited resources will survive and have more offspring than those individuals with variations that are less able to compete.
- This will lead to change in populations over generations in a process that Darwin called "descent with modification," or evolution.
- The birds have inherited variation in the bill shape with some individuals having wide, deep bills and others having thinner bills.
- The Grants had studied the inheritance of bill sizes and knew that the surviving large-billed birds would tend to produce offspring with larger bills, so the selection would lead to evolution of bill size.
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- Scientists use the phrase "descent with modification" because even though related organisms have many of the same characteristics and genetic codes, changes occur.
- With new traits, a new branch point is determined (go back to step 1 and repeat).
- Organizing the evolutionary relationships of all life on earth proves much more difficult: scientists must span enormous blocks of time and work with information from long-extinct organisms.
- For scientists deciphering evolutionary pathways, the same idea is used: the pathway of evolution probably includes the fewest major events that coincide with the evidence at hand.
- Starting with all of the homologous traits in a group of organisms, scientists look for the most obvious and simple order of evolutionary events that led to the occurrence of those traits.
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- Common in cancer cells, silencing genes, which occur through epigenetic mechanisms, include modifications to histone proteins and DNA.
- Cancer epigenetics is the study of epigenetic modifications to the genome of cancer cells that do not involve a change in the nucleotide sequence.
- Silencing genes through epigenetic mechanisms is very common in cancer cells and include modifications to histone proteins and DNA that are associated with silenced genes.
- When these modifications occur, the gene present in that chromosomal region is silenced.
- Mechanisms can include modifications to histone proteins and DNA associated with these silencing genes.
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- Stem modifications, either aboveground, underground, or aerial, enable plants to survive in particular habitats and environments.
- Modifications to the aerial stems, vegetative buds, and floral buds of plants perform functions such as climbing, protection, and synthesis of food vegetative propagation .
- Aerial modifications of stems include the following:
- Stem modifications enable plants to thrive in a variety of environments.
- Found in southeastern United States, (a) buckwheat vine (Brunnichia ovata) is a weedy plant that climbs with the aid of tendrils.
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- Proteins can be chemically modified with the addition of methyl, phosphate, acetyl, and ubiquitin groups.
- Chemical modifications occur in response to external stimuli such as stress, the lack of nutrients, heat, or ultraviolet light exposure.
- Another example of chemical modifications affecting protein activity include the addition or removal of methyl groups.
- Methyl groups are added to proteins via the process of methylation; this is the most common form of post-translational modification.
- Proteins with ubiquitin tags are marked for degradation within the proteasome.
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- Social insects, such as worker bees, have no ability to reproduce, yet they maintain the queen so she can populate the hive with her offspring.
- Although a gene obviously cannot be selfish in the human sense, it may appear that way if the sacrifice of an individual benefits related individuals that share genes that are identical by descent (present in relatives because of common lineage).
- Even less-related individuals (those with less genetic identity than that shared by parent and offspring) benefit from seemingly altruistic behavior.
- However, these behaviors may not be truly defined as altruism in these cases because the actor is actually increasing its own fitness either directly (through its own offspring) or indirectly (through the inclusive fitness it gains through relatives that share genes with it).
- According to evolutionary game theory, a modification of classical game theory in mathematics, many of these so-called "altruistic behaviors" are not altruistic at all.
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- There are many examples of translational or post-translational modifications of proteins that arise in cancer.
- Modifications are found in cancer cells from the increased translation of a protein to changes in protein phosphorylation to alternative splice variants of a protein.
- With an increased understanding of gene regulation and gene function, medicines can be designed to specifically target diseased cells without harming healthy cells.
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- These are stretches with a high frequency of cytosine and guanine dinucleotide DNA pairs (CG) found in the promoter regions of genes.
- This modification changes how the DNA interacts with proteins, including the histone proteins that control access to the region.
- Highly-methylated (hypermethylated) DNA regions with deacetylated histones are tightly coiled and transcriptionally inactive.
- Modifications to the histones and DNA affect nucleosome spacing.
- Modifications affect nucleosome spacing and gene expression.