Transcript File - NCEA Level 2 Biology

Genetic change
Darwin
Evolution and the theory
Gene pool variation
Natural selection
Genetic drift – founders effect, bottleneck effect
So far………
• We have looked at Genetic variation
 Meiosis – crossing over, recombinant
 Meiosis – segregation
 Meiosis – independent assortment
 Mutations
 Mendelian Genetics – monohybrid cross, dihybrid cross,
test cross ( do not use the words back cross)
Now we are looking at Genetic change
- a permanent change in the gene pool of the population over a
period of time (Evolution)
Evolution
• This is the process by which new species of plants
and animals develop from earlier forms
• The process of evolution normally occurs slowly,
usually in response to a change in a species’
environment
• Evolution proceeds by changes in the frequency of
alleles in a population – some alleles do better
than others
What is evolution?
 Evolution refers to the permanent genetic
change (change in gene frequencies) in
population of individuals.
 It does not refer to changes occurring to individuals within their
own lifetimes. Populations evolve, not individuals.
 Evolution is not a belief system. It is a scientific
concept.
 Evolution is a theory…but you don’t get any
better than that in science
 Theory: a well-substantiated explanation that
incorporates facts, laws, inferences and tested
hypotheses.
Recall these keywords
• Gene pool: all the genes carried by
a population at a certain time
– e.g the all the genes of the fantails in
the south Island make up a gene pool
• Allele frequency: within a
population each allele exists at a
particular frequency. It is calculated
by a simple formula
• Evolution occurs when frequencies of
alleles change over time.
And these….
• Species a grouping of organisms that can interbreed
and are reproductively isolated from other such
groups
• Population: comprises the total number of one
species in a particular area.All members of a population
have the potential to interact with each other. This
includes breeding.
Compare – genetic change & genetic variation
• Genetic variation: is the result of two processes
• Creation of new genes by mutation
• Reshuffling of existing genes in sexual reproduction
• Genetic change: changes in the gene pool
occurring over successive generations
• Mutation
• Natural Selection
• Mate Selection
• Migration
• Genetic drift
Modelling Genetic Change
methods
• You are given a gene pool of individuals
showing variation for skin colour. The alleles
are given on the sheet of paper in your tray. If
nothing affected this gene pool over time, the
allele frequency would remain constant.
Count your alleles to start with and write
them down.
Natural Selection
• Choose a predator for your group. They will be
asked to pick out one at a time as many
individuals as they can in 1 minute. After each
picking they must spin around once before
picking the next one.
• Now count your alleles, have the ratios
changed? Why?
• Natural selection is the passing on of alleles
which are the fittest. Which were the most fit
alleles in your tray?
Migration
• For the alleles that have been eaten, replace
with new alleles selected at random from your
bag.
• This time you will choose an allele with your
eyes closed and one person will take it to
another tray.
• You may repeat this 10 times.
• Now count and record your alleles.
Genetic Drift
• Genetic Drift occurs when a part of a
population is cut off or separated from the
rest.
• Using the current population, shake your tray
then place a ruler over the tray with your eyes
closed. Everything to the left of the ruler dies
and need to be removed from the tray.
• Count and record your remaining alleles in the
population. Have any alleles died out?
Mate Selection
• Green alleles are considered desirable
individuals and mate with yellow alleles. Pair
these up.
• Red alleles mate with purple alleles. Pair these
up.
• Any remaining alleles die and need to be
removed. What is left?
Keywords
Microevolution describes the small-scale changes
within gene pools over generations.
Macroevolution is the term used to describe large
scale changes in form, as viewed in the fossil record,
involving whole groups of species and genera.
Natural selection: Individuals which have alleles
which are more fit than others in the gene pool will
survive and go on to reproduce, passing on those fit
alleles.
Deme: A local unit of population living in a particular
area, genetically isolated from other populations.
Theory of Evolution
• Charles Darwin is credited with the development
of the theory of evolution by natural selection,
there were many other who contributed.
• There is a time line of beliefs and scientific
argument
History of Evolutionary Thought
Hebert Spencer
1820 - 1903
Proposed concept of the
‘survival of the fittest’
Erasmus Darwin
1731 - 1802
Charles Darwin's grandfather
and probably an important
influence in developing his
thoughts on evolution.
John Baptiste de Lamarck
1744 - 1829
First to publish a reasoned theory
of evolution. Proposed idea of
use and disuse and inheritance of
acquired characteristics.
Rev. Thomas Malthus
1766 - 1834
Wrote: ‘An Essay on the
Principles of Population’,
attempting to justify the
squalid conditions of the
poor.
Charles Lyell
1797 - 1875
Major influence on Darwin.
Lyell’s work ‘Principles of Geology’
proposed that the earth is very old.
Alfred Russel Wallace
1823 - 1913
‘Theory of Natural Selection’
Charles Darwin
1809 - 1882
‘Theory of Evolution
by Natural Selection’
August Weismann
1834 - 1914
Proposed chromosomes as the
basis of heredity, demolishing the
theory that acquired
characteristics could be inherited.
R.A. Fisher 1890-1962
J.B.S. Haldane
Sewall Wright1889-1988
Julian Huxley 1887-1975
Ernst Mayr
1904-2005
T. Dobzhansky
The New Synthesis
1898-1964
Founding of population genetics and
mathematical aspects of evolution and genetics.
Gregor Mendel
1822 - 1884
Developed the
fundamentals of the genetic
basis of inheritance.
Neo-Darwinism: The version of Darwin’s
theory refined and developed in the light of
modern biological knowledge (especially
genetics) in the mid-20th century
1900-197
Collaborated to formulate the modern
theory of evolution, incorporating
developments in genetics,
paleontology and other branches of
biology.
Old Theories of Evolution
• Jean Baptiste Lamarck (early 1800’s) proposed:
“The inheritance of acquired characteristics”
• He proposed that by using or not using its body parts,
an individual tends to develop certain characteristics,
which it passes on to its offspring.
“The Inheritance of Acquired
Characteristics”
• Example:
A giraffe acquired its long neck because its ancestor
stretched higher and higher into the trees to reach
leaves, and that the animal’s increasingly lengthened
neck was passed on to its offspring.
Charles Darwin
• Influenced by Charles Lyell who published
“Principles of Geology”.
• This publication led Darwin to realize that
natural forces gradually change Earth’s
surface and that the forces of the past are
still operating in modern times.
Charles Darwin
• Darwin set sail on the H.M.S. Beagle (18311836) to survey the south seas (mainly
South America and the Galapagos Islands)
to collect plants and animals.
• On the Galapagos Islands, Darwin
observed species that lived no where else
in the world.
• These observations led Darwin to write a
book.
• http://science.howstuffworks.com/life/297
86-100-greatest-discoveries-naturalselection-video.htm
Darwin discovered these after his
voyage…
Charles Darwin
• Wrote in 1859: “On the Origin of Species by Means
of Natural Selection”
• Two main points:
1. Species were not created in their present form,
but evolved from ancestral species.
2. Proposed a mechanism for evolution:
NATURAL SELECTION
Natural Selection
Overproduction
Variation
Populations produce too
many young: many must die
Individuals show variation:
some variationsare more
favorable than others
Natural Selection
Natural selection favors
the best suited at the time
Inheritance
Variations are
inherited. The best
suited variants
leave more
offspring.
Charles Darwin theory of evolution by natural
selection was based on:
1. Overproduction
Organisms have high reproductive rates – often producing more offspring than
needed. This lead to struggle for survival among offspring
2. Variation
Among offspring there was variation in all characteristics. Variation in phenotype
therefore genotype
3. Favourable variations
Organisms with favourable variations better able to survive and pass on those
favourable characteristic to offspring
4. Survival of the fittest
Over time each successive generation will be better adapted to the environment
5. Evolution
Eventually new species evolve from old by the process Darwin called “Natural
Selection”
Summary of Darwin’s Theory:
Natural selection can provide the means for a
species to change over time because natural
selection will always favour the most adaptive
phenotypes (therefore genotypes). More
favourable phenotypes will have greater
reproductive success and will become
proportionally more abundant in the
population. Over time, favourable phenotypes
will predominate and the unfavourable
phenotypes will become rare.
Video
• http://www.youtube.com/watch?v=7w57_P9
DZJ4
• http://www.youtube.com/watch?v=VSevMUX1QQ