Transcript Natural Selection and Selective Breeding

Natural Selection and Selective
Breeding
7th Grade Science
Engage: What are adaptations?
• Scholastic Study Jams:
http://studyjams.scholastic.com/studyjams/ja
ms/science/animals/animal-adaptations.htm
The Arctic Hare
Natural Selection
• Natural Selection- a process by which
organisms change over time as those with
traits best suited to an environment pass their
traits to the next generation.
Charles Darwin
• Scientist that observed and
studied 13 species of finches on the
Galapagos Islands.
• His main points
– Organisms produce more offspring than can
survive.
– There is competition among offspring for food,
space, and other resources.
Charles Darwin
– There is natural variety (difference) among the
offspring of an organism. These variations are
caused mainly by genetic differences.
– Individuals with certain traits are better suited to
survive in their environment than those without
the traits.
– Organisms that survive and reproduce pass the
genes for their traits on to the next generation.
Charles Darwin Biography
• http://app.discoveryeducation.com/search?Nt
t=charles+darwin
Natural Selection
• Natural selection is possible because of
genetic variation among individual organisms
within a population.
– Over generations, traits that enhance survival (i.e.
are favorable in their environment) of a species
are selected over those that do not. When all
members of a population have the favorable trait,
it is called an adaptation.
Natural Selection: Adapations
Natural Selection
• Natural selection changes every species found
on Earth.
• In the Galapagos Islands off the coast of
Ecuador, the Galapagos Medium Ground Finch
has developed a beak shape that is very
different from other finches found in the same
islands.
– Adaptations to the shape of a bird’s beak occur
due to different food sources.
Darwin’s Finches
The Peppered Moth
• Natural Selection at
work:
– The Peppered Moth
– http://www.techapps.ne
t/interactives/pepperMo
ths.swf.
– https://www.youtube.co
m/watch?v=sVVldxxbWi
g
Natural Selection: The Peppered Moth
• When newly industrialized parts of Britain
became polluted in the nineteenth century,
smoke killed lichens growing on trees and
blackened their bark.
• Pale colored moths which had been well
camouflaged before when they rested on tree
trunks became very conspicuous and were
eaten by birds.
Peppered Moth
Natural Selection: The Peppered Moth
• Rare dark moths, which had been conspicuous
before, were now well camouflaged in the
black background.
• As birds switched from eating mainly dark
moths to mainly pale moths, the most
common moth color changed from pale to
dark.
• Natural selection had caused a change in the
British moth population. The moths had
evolved.
The Peppered Moth
Variation
• Variation- is a property of a population that
occurs when individuals within a population
differ in the characteristics.
Variation
• Variation can be observed by:
– External features- features are those traits that are easily
observed.
– Behaviors- activities or actions that generally help an
organism survive in its environment.
– Physiology- the study of the internal structures and
functions of an organism.
Selective Breeding
• Selective Breeding- A form of artificial
selection whereby deliberate breeding results
in desired traits in plants and animals.
Dogs
Cats
Cattle
Pigeons
Teosinte to corn
Selective breeding of corn!
Chickens
Chicken Eggs
Apples
Selective Breeding
• Selective breeding of particular genes runs the
risk of losing some of the other genes from the
gene pool altogether, which is IRREVERSIBLE.
– This is INBREEDING DEPRESSION, where the exclusivity
of the advantageous genes means that some other less
desirable genes are phased out.
– Genetic diversity in the long term is reduced, because
many organisms end up with similar genetic material
due breeding with each other constantly.
Problems with Selective Breeding
• Bloodhounds develop loose skin around their
eyes, increasing the potential unwanted small
objects getting stuck in their eyes
Problems with Selective Breeding
• Centuries of selective breeding has led to the
creation of many different breeds of animal all
inheriting very similar characteristics to the previous
generation, which may include genetic diseases.
(Many King Charles Cavaliers develop heart murmurs
and other heart problems, cruelly cutting their lives
short)
Problems with Selective Breeding
• Bulldogs develop oversized heads which result
in many having to be born through caesarean
section
• Pekingese dogs have very short faces, making
it hard for them to breath or smell
Labrador Retrievers
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Retrieve birds for hunters
Sniff out drugs
Sniff out bombs
Sniff out people buried under rubble
Sniff out deer antlers to use to make knife
handles...
• Seeing eye dogs
• Therapy dogs