Evolution The change in life forms over time
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Transcript of Evolution The change in life forms over time
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EvolutionThe change in life forms
over timehttp://evolution.berkeley.edu/evolibrary/
home.php
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Natural Selection Lab
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Generation 1In
divi
dual
s
Color Trait
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Generation 2In
divi
dual
s
Color Trait
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Generation 3In
divi
dual
s
Color Trait
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Generation 4In
divi
dual
s
Color Trait
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Variations Among Individuals
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Struggle for Survival
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Survival of Fittest Must Survive
Eaten by predators
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Fittest Pass Their Traits to Their Offspring
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Industrial Melanism
•Shift in phenotype frequencies
•Light colored moths were reduced and dark color became predominant
•Birds preyed on the light colored moths
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Peppered moths on tree trunk
Natural selection – the peppered moth
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Dark coloured peppered moth
Natural selection – the peppered moth
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Pale coloured, speckled peppered moth
Natural selection – the peppered moth
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Five Tenets of Evolution by Natural Selection
Variations among individuals, Large numbers of offspring,
Struggle for survival, Survival of fittest must reproduce
Fittest pass on their traits to their offspring
SOOO What are traits??????
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Population- group of organisms of the SAME species; and occupies certain area at the same time
Species- organisms that can INTERBREED and produce FERTILE offspring
What is a Species?
• A group of actually or potentially interbreeding populations (isolated from other groups)
• Gene flow can occur between populations of the same species
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CO 13
Chap 13DNA
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Nucleic acidsDNA (deoxyribonucleic acid)RNA (ribonucleic acid)
NUCLEOTIDES (found in nuclein)Contain a sugar, phosphate and a nitrogen base
Adenine
Guanine
Cytosine
Thymine
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Nucleic Acid Structure
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DNA: THE DOUBLE HELIX
•Steps of ladder are bases (A, T, G, C)
•Sides of ladder are sugar & phosphate
•Both sides held together by hydrogen bonds
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Some interesting facts: A sequence of bases (A’s, C’s, G’s, and T’s) that code for a protein is called a gene
All of the base pairs along all the chromosomes in an organisms are that organisms genome
95% of the A’s, C’s, G’s and T’s do not code for any proteins – only 5% of DNA sequence in a genome are genes.
Genome Sizes vary from species to species. The human genome contains over 3 Billion bases (A’s, C’s, G’s, and T’s).The Human genome contains about 35,000 different geneseach consisting of about 27,000 base pairs.
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When a cell is dividing, DNA winds up tightly and forms chromosomes in the nucleus of the cell.
The genes are contained within the chromosome.
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A karyotype is a picture showing the arrangement of a full set of chromosomes.
Humans have 46 (or 23 pairs) of chromosomes
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Alleles are forms of genes on chromosomes- Alleles – chromosome sections that code for specific proteins traits
Each cell has two chromosomes with forms of genes on each.
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Examples of alleles: Humans have alleles for
blue eyes / brown eyes /green eyes
curly/straight hair
blood type A / B / O / AB
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The gene pool is the set of all genes, or genetic information, in any population, usually of a particular species . This also proves to be the basic level at which evolution occurs.Populations have alleles Gene pool – total of all the allele in the population
Gene pool – total of all the allele in the population
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18.1 MICROEVOLUTION
Population -- all the members of a single speciesEvolution that occurs within a population = microevolutionPopulation genetics – studies variations in gene pools
Code is responsible for the phenotype- expression of the gene
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EvolutionChanges in genetic makeup of a population
The basic mechanisms of evolution
Natural selection, mutation, and migration- Along with
Genetic Drift
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A. Causes of Evolution of Populations…
1. Genetic Mutations
a ) Polymorphism (two or more distinct phenotypes)b) blood types, eye color..etcc) Mutations (can be harmful or beneficial)
d) Some mutations may at first appear harmful, but give an advantage if the environment changes. -- this is referred to as RELATIVE FITNESS
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Figure 18.3
• Each rat snake represents a separate population of snakes
• These snake remain similar and can interbreed• This keeps their gene pools somewhat similar• They are considered subspecies
Example of GENE FLOW
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Genetic Drift
In each generation, some individuals may, just by chance, leave behind a few more descendents (and genes, of course!) than other individuals. The genes of the next generation will be the genes of the “lucky” individuals, not necessarily the healthier or “better” individuals. That, in a nutshell, is genetic drift. It happens to ALL populations—there’s no avoiding the vagaries of chance.
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How is this different from Natural Selection?
What will the next generation look like?
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More Brown beetles, not because they are better adapted but by chance…
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GENETIC DRIFTRefers to changes in allele frequencies, usually in small populationsOccurs when founders start a new population or after a bottleneck
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Bottleneck Effect – caused by a severe reduction in population, reduces overall diversity. Ex Cheetah
Most alleles are yellow!
Youtubebottleneck effect –lego population
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FOUNDER EFFECT
The founder effect is an example of genetic drift where rare alleles or combinations occur in higher frequency in a population isolated from the general population.
Dwarfism in Amish communities
Due to few German founders
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Investigating Bottleneck Effect
Trying to identify if a population is going through genetic drift is quite tough because it is such a slow procedure.
Once the population that has survived the bottleneck reproduces the allele frequency compared to the parent population will be completely different.
Look at some case studies to investigate whether an event in the1860s that limited genetic variation among Navajos may have led to both children of a modern-day Navajo couple being born with a rare genetic disease called XP (the abbreviation for xeroderma pigmentosum).