Genomics Video 2
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Genomics Video 2


Genomics: Observing Evolution The Big Idea The evolutionary history of a species —how it arose and
changed over time—is written in its genome. Studying the genomes of many species enables us to look back in time
and trace how life has changed over the span of earth’s history. Evolution occurs at different scales. Microevolution refers
to changes within a species, such as becoming better adapted to
circumstances over many generations. Macroevolution is
change on a larger scale, like the evolution of a new species
or the extinction of another. Evolution happens as the result of several mechanisms. Genetic drift is the result of chance events,
like natural disasters. As the result of a metaphorical “roll of the dice,”
some individuals do not survive to reproduce, so their particular genetic makeup is not passed on. Recombination happens when organisms reproduce sexually. In the same way that shuffling a deck of cards
results in a new sequence to the deck, recombination leads to new sequences
and gene combinations in every generation. Gene flow, or migration, is the movement of individuals
and their genes from one region to another. When plants or animals, including people, move to a new area,
they may introduce new gene variations into that population. This is a very important source of genetic diversity. A mutation is any change in an organism’s DNA. For example, when a cell divides,
the DNA may fail to copy accurately. Environmental factors, such as exposure to
certain chemicals or radiation, can change DNA. When a cell repairs itself,
it may not do a perfect job, resulting in a mutation. And foreign DNA may be inserted into a genome
when a virus attacks an organism—another mutation. As a result of genetic variation
produced by these mechanisms, some individuals are better adapted
to the environment in which they live than others. They can produce more offspring
who also survive to reproduce. This process is called natural selection. While mutations are
random and sudden; natural selection is systematic
and happens over generations. Think about underwater predators,
like sharks, dolphins, and killer whales. They all live in water and chase their prey. Random mutations result in individuals with a variety of shapes. Natural selection is the process by which the individuals
with shapes that allow them to move faster and more efficiently survive and reproduce in greater numbers. The result of mutations and natural selection is that
underwater predators have evolved a streamlined shape. In a sense, natural selection is the real-world testing
and evaluating of the effect of mutations. For centuries, scientists classified species according
to characteristics they could observe with their eyes. Genomics is a tool that enables scientists to examine species
at the molecular level by looking at DNA sequences. This has led to much deeper understanding about how organisms
are related to one another and to many surprises. For example, exchanges of genes between different species
are now known to be far more common than previously expected. Even many modern humans have segments of DNA
that came from another species: Neanderthals. We now know that the notion of a “tree of life” with new species branching off in a clean, tree-like shape does not reflect what is really going on. Genomics has revealed that the reality of how species
are related to one another is far messier.

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