EvolutionThe change in life forms

over timehttp://evolution.berkeley.edu/evolibrary/

home.php

Natural Selection Lab

Generation 1In

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Color Trait

Generation 2In

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Generation 3In

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Generation 4In

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Variations Among Individuals

Struggle for Survival

Survival of Fittest Must Survive

Eaten by predators

Fittest Pass Their Traits to Their Offspring

Industrial Melanism

•Shift in phenotype frequencies

•Light colored moths were reduced and dark color became predominant

•Birds preyed on the light colored moths

Peppered moths on tree trunk

Natural selection – the peppered moth

Dark coloured peppered moth

Natural selection – the peppered moth

Pale coloured, speckled peppered moth

Natural selection – the peppered moth

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??????

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

CO 13

Chap 13DNA

Nucleic acidsDNA (deoxyribonucleic acid)RNA (ribonucleic acid)

NUCLEOTIDES (found in nuclein)Contain a sugar, phosphate and a nitrogen base

Adenine

Guanine

Cytosine

Thymine

Nucleic Acid Structure

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

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.

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.

A karyotype is a picture showing the arrangement of a full set of chromosomes.

Humans have 46 (or 23 pairs) of chromosomes

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.

Examples of alleles: Humans have alleles for

blue eyes / brown eyes /green eyes 

curly/straight hair

blood type A / B / O / AB

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

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

EvolutionChanges in genetic makeup of a population

The basic mechanisms of evolution

Natural selection, mutation, and migration- Along with

Genetic Drift

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

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

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?

More Brown beetles, not because they are better adapted but by chance…

GENETIC DRIFTRefers to changes in allele frequencies, usually in small populationsOccurs when founders start a new population or after a bottleneck

Bottleneck Effect – caused by a severe reduction in population, reduces overall diversity. Ex Cheetah

Most alleles are yellow!

Youtubebottleneck effect –lego population

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

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).