Natural selection and Evolution. What is this all about? video

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?

Val His Leu Thr Pro Glu Lys … 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 = adenineT = thymineG = guanineC = 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 acidProtein = 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

Val His Leu Thr Pro Glu Lys … 139 more

Val His Leu Thr Pro Val Lys … 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.

H h

H HH Hh

h Hh 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?


• 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


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.


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.


• 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

http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_14

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

Rep

rod

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d

Gen

es


• 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.

Variationarises from

Mutation:new genes

Sexual Recombination: new gene combinations


• Environmental selection pressure: affects the survival and reproduction of individuals in a population differently (think back to the beetles)


• 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.


• What does fittest mean?– To a biologist?– To the public?


• What does fittest mean?– To a biologist?

• = differential reproductive success

– To the public?• = biggest, strongest, ….


• 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 ….

Artificial Selection

Types of evolution

• 1. Divergent evolution• 2. Convergent evolution• 3. Co-evolution

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).

Divergent Evolution

Divergent Evolution

Divergent Evolution

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:

Divergent Evolution

http://www.biology-online.org/images/darwin_finches.jpg

Divergent Evolution

• 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


Fish Reptile MammalWhat is the similar selection pressure?



What is the similar selection pressure?

http://www.votawphotography.com/photo/Animals/animals.htm

http://www.hundekosmos.de/images/greyhound_517.jpg

Speed to catch prey (cheetah) and speed to win races and be bred.


MarsupialMammals

Placental Mammals


“Ant eaters” of the world


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 legsGood hearing

Sharp eyesight

Coevolution

CoevolutionBird Bites

Eye Spot

Real Eye

What type of myth does this illustrate?


• That need creates the genetic change



Good and bad gene myth. (only differential reproductive success).

Vicious cycle

• Pesticide resistance cycle• Antibiotic resistance cycle

Documents

Natural selection and Evolution. What is this all about? video