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Lesson 5: Prevention and Behavior Change, and Evolution and Genetics -
=>
Evolution - - Charles Darwin embarked on a sea voyage to South
America in 1831. He noticed while visiting the Galapagos Islands that
finches th...
Lesson 5: Prevention and Behavior Change, and Evolution and Genetics -
✔✔=>
Evolution - ✔✔- Charles Darwin embarked on a sea voyage to South
America in 1831. He noticed while visiting the Galapagos Islands that
finches that lived on the different islands appeared to have beaks that were
perfectly suited for cracking open the seeds found on the island they lived
on.
- These types of observations led Darwin to his ideas about how organisms
change over time (evolution).
- Darwin hypothesized that as populations grow, they inevitably must reach
a point where there will be more members of the population than the
resources in the environment can support.
,- Darwin argued that some organisms are naturally more capable of
obtaining resources than others. Thus, those organisms will be most likely
to obtain enough resources to survive and reproduce, while those that are
less capable will die. Because the more capable organisms can survive
and reproduce, their traits will be more likely to be passed on to the next
generation.
- Evolution helps us to understand the ways in which organisms change,
and the pressures that keep certain traits in a population for a long period
of time. Evolution doesn't create species that are constantly changing for
the better, it creates a situation where populations evolve to take
advantage of their environments.
- Therefore, evolution doesn't have a goal and doesn't always involve
organisms getting stronger or smarter. Organisms change to take
advantage of their environment and, if they can do that,, they may not
evolve for a long time.
Natural Selection and Sexual Selection - ✔✔- Natural selection was the
term Darwin used to describe the process by which organisms with
,favorable traits were "selected" to survive and reproduce, while those
without such traits were less likely to do so.
- Sexual selection occurs simply because it is found to be attractive to the
opposite sex. This form of selection helps to explain things like peacock's
feathers, which don't promote survival but still are associated with
increased reproductive rates.
- Alfred Russel Wallace came up with some of the same ideas Darwin did
at around the same time. Darwin's ideas were more fully formulated,
however, and he had gathered more evidence to support them, so he got
the credit.
- Darwin's ideas were first published in 1859, in a work titled On the Origin
of Species by Means of Natural Selection
Genetics - ✔✔- Darwin's ideas of evolution helped to explain the forces that
led to organisms changing over time, but they didn't explain how traits were
passed down from parent to offspring.
, - Then, experiments over the first half of the 20th century pointed scientists
to the hypothesis that heritable information was stored inside an organism's
cells, in deoxyribonucleic acid (DNA).
Chromosomes and Genes - ✔✔- DNA is found in the nuclei of the cells,
wrapped up with proteins in structures called chromosomes. The DNA can
be divided into functional segments, each which acts as a recipe book to
produce proteins.
- The functional segments of DNA are known as genes.
- During the reproductive process, each person inherits 23 chromosomes
from his or her mother and 23 chromosomes from his or her father,
resulting in 46 chromosomes (23 pairs) altogether.
- Each collection of 23 chromosomes contains a copy of every gene in the
human genome (all the genetic information of an individual), which are
estimated to total around 20,000 genes.
Alleles - ✔✔Different forms of genes that result in variations in the structure
and function of proteins that result from that gene's expression, or
translation into a protein, are called alleles.
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