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Natural selection and Evolution
What is this all about? video
Traits Traits are passed from one generation to the next That means that all the information to produce all of your traits was contained within the single cell that was you when you were conceived. What determines your traits?
Proteins Proteins determine our traits Each protein is a sequence of amino acids. Which amino acids and in which order determines the structure and function of the protein. How are proteins produced? ValHisLeuThrProGluLys … 139 more Hemoglobin: a protein that is 146 amino acids long
DNA DNA is the blueprint or recipe book for making proteins (and therefore traits). This is what is passed on from one generation to the next. How does DNA code for proteins, thus traits? Proteins DNA Traits
It is composed of four types of nucleotides: A Adenine T Thymine G Guanine C Cytosine From this four letter alphabet different amino acids are specified. DNA is arranged as a double helix
Nucleotides DNA is composed of nucleotides: the information part of the DNA. There are only 4 types of nucleotides in DNA: A, T, G, and C A = adenine T = thymine G = guanine C = cytosine From this four letter alphabet different amino acids are specified
More on DNA A - T every three nucleotides A - T (codon) codes for one of the T - A 20 amino acids C - G (and there are 1000s G - C of nucleotides in a T - A strand of DNA) There are also sequences of 3 nucleotides that specify where to start and where to stop reading along the DNA to make the protein. This is called translation.
THE GENETIC CODE Thymine (T) is replaced with Uracil (U) in messenger RNA.
More on DNA A - T So another definition A - T of DNA is a sequence T - A of 1000s of nucleotides C - G in a double strand that G - C is the recipe for amino T - A acids and therefore proteins
Three processes REPLICATION –Synthesis of two DNA molecules from DNA template TRANSCRIPTION –Synthesis of RNA molecule from DNA template TRANSLATION –Synthesis of a protein from RNA template
Genes are translated into proteins based on a triplet code Transcription Codon = 3 bases Translation Amino acid Protein = many amino acids strung together
Recap DNA is composed of nucleotides –There are only 4 types of nucleotides Every 3 nucleotides codes for an amino acid –There are 20 different amino acids Strands of amino acids form proteins Proteins are responsible for traits and adaptations… Video on DNA translation Video2 on DNA translation
Chromosomes So what is a chromosome?
Chromosomes So what is a chromosome? –Strands of DNA, all tightly wrapped up and existing in a cell’s nucleus [Humans have 46 chromosomes, 23 from each parent?]
Genes So what is a gene?
Genes are a particular segment of DNA, that code for a protein (usually). Junk DNA
Genes So what is a gene? –A section of DNA that encodes information for building a protein (or RNA molecule) –Each chromosome can have thousands of genes on it.
Mutations What is a mutation?
Mutations What is a mutation? –A change in the sequence of nucleotides in a gene. –They are random, caused by Chemicals, radiation, copying errors –They change the protein that is specified May be beneficial, neutral, harmful, or lethal
Alleles are variants of genes
Sickle cell disease Occurs due to a mutation in the gene that codes for the hemoglobin protein. protein that carries oxygen in red blood cells. Causes the normally round red blood cell to change into a sickle shape that no longer carries oxygen as well. This can be lethal. Red blood cells of affected individuals distort in shape, break down or clog blood vessels and cause pain, poor circulation, etc ValHisLeuThrProGluLys … 139 more ValHisLeuThrProValLys … 139 more
Sickle cell disease Alleles: different versions of genes. –Sickle cell allele (h) –“normal” allele (H) –Sickle Cell Anemia (hh): often lethal –Sickle Cell Trait (Hh): symptoms vary, usually very little effects. Hh HHHHh h hh Mom Dad
Sickle cell disease Is having the sickle cell allele good or bad?
Sickle cell disease Is having the sickle cell allele good or bad? –It depends on the environment!! –The sickle cell allele confers genetic resistance to malaria, one of the biggest killers of infants in areas with malaria. So, where do you think you find populations with the highest incidence of the sickle cell allele? Malaria areas PBS Video
Some more genetic diseases mapped List
Gene pool Gene Pool: all of the alleles and their proportions in a population.
Gene pool Gene pools change over time. 0%100%80%20% Environmental Change – Pesticide introduced Resistant Gene
Gene pool A change in a gene pool over time is called what?
Evolution Genetic Evolution: a change in a gene pool –Note: this operates at the population level! Another definition is a genetic change in a population.
Mechanisms of evolution What causes gene pools to change?
Mechanisms of evolution What causes gene pools to change over time? 1. Mutations: produce new alleles and new genes. –are random –cannot be predicted ahead of time –create genetic variety –may be beneficial, neutral, or harmful to the individuals that inherit them
Mechanisms of evolution 2. Migration (immigration/emigration). –Technical term is gene flow. –The movement of alleles between populations as a result of movement of individuals from one population to another.
Mechanisms of evolution 3. Chance: when chance, rather than traits determine reproductive success. Example: disaster that kills part of a population. Small populations are more susceptible to big evolutionary change due to chance. Technical term is Genetic Drift.
Mechanisms of evolution 4. Natural Selection. When traits determine reproductive success; traits in more reproductively successful individuals get passed on more into the next generation.
Natural Selection Natural Selection. Alleles that confer “success” are more likely to be passed on to future generations and will increase their % relative to other alleles over time. Technical term for “success” is differential reproductive success.
Example of Natural Selection Gene pools change over time. 0%100%80%20% Environmental Change – Pesticide introduced Resistant Allele Non-Resistant Allele Alleles
Example of natural selection Beetles and pesticide resistance –The resistant and non-resistant alleles were due to past mutations that created genetic variety in the beetles but were neutral until now (pesticide spraying time). –The pesticide acted as a new environmental selection pressure that selected for the resistant allele. –This selection pressure, causing individuals with the resistant allele to out-survive and out-reproduce individuals without the resistant allele, resulting in an increase in individuals with the resistant allele in the next generation.
Natural selection flowchart Mutation New Genes Random Recombination New combinations of existing genes Sexual reproduction Genetic Variability—Gene Pool Current mix of genes in population Environmental Selection Pressures Examples: climate, predation, mate selection Differential Survival Some genes and gene combinations help the individual survive better than other individuals. Differential Reproduction Some genes and gene combinations help the individual reproduce better than other individuals Reproduced Genes
Natural selection flowchart Mutation and recombination create genetic variety in gene pool of a population. Mutations: create new alleles/genes. Recombination: sexual reproduction mixes alleles and creates new combinations of alleles.
Variation arises from Mutation: new genes Sexual Recombination: new gene combinations
Natural selection flowchart Environmental selection pressure: affects the survival and reproduction of individuals in a population differently (think back to the beetles)
Natural selection flowchart Environmental selection pressure leads to differential survival and differential reproduction of individuals with more successful alleles. This is passed on to future generations and changes the gene pool through time.
“evolution: survival of the fittest” Isn’t that what we were taught in school? Well, its wrong. This is an example of science being misinterpreted by the public.
“evolution: survival of the fittest” What does fittest mean? –To a biologist? –To the public?
“evolution: survival of the fittest” What does fittest mean? –To a biologist? = differential reproductive success –To the public? = biggest, strongest, ….
“evolution: survival of the fittest” What does fittest mean? –To a biologist? = differential reproductive success –To the public? = biggest, strongest, …. ALL that really matters is whether or not your genes are passed on to future generations ….
Divergent Evolution 1. Divergent evolution –Two different populations of a species that experience different selection pressures may as a result become genetically different from one another Once in a very great while, the two populations will become so different that they cannot reproduce together anymore (this then becomes speciation).
One or more populations whose members actually or potentially interbreed under natural conditions and that are reproductively isolated from other such groups. Species and Speciation Review: Definition of Species:
2. Convergent evolution –Start with two very different species; they experience similar selection pressures and through time come to look and/or behave similarly. Convergent Evolution
FishReptileMammal What is the similar selection pressure?
What is the similar selection pressure? /photo/Animals/animals.htm Speed to catch prey (cheetah) and speed to win races and be bred.
Convergent Evolution Many plants look like cacti because they also have evolved to store and defend water but they are not cacti – for example, the ocotillo is not a cactus, it is a shrub in a different plant family.
Types of evolution 3. Co-evolution –Two species that interact with each other (predator/prey; mutualistic; parasite/host; …) and act as selection pressures on one another –“Evolutionary Arms Race” Long legs Good hearing Sharp eyesight
Bird Bites Eye Spot Real Eye
What type of myth does this illustrate?
That need creates the genetic change
What type of myth does this illustrate?
Good and bad gene myth. (only differential reproductive success).