Download PPT IntroGenetics

Evolution
The change in life forms over time
http://evolution.berkeley.edu/evolibrary/home.php
Natural Selection Lab
Individuals
Generation 1
Color Trait
Individuals
Generation 2
Color Trait
Individuals
Generation 3
Color Trait
Individuals
Generation 4
Color Trait
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
Natural selection – the peppered moth
Peppered moths on tree trunk
Natural selection – the peppered moth
Dark coloured peppered moth
Natural selection – the peppered moth
Pale coloured, speckled 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 13
DNA
Nucleic acids
DNA (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 genes
each 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 chromosomesAlleles – 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 species
Evolution that occurs within a population = microevolution
Population genetics – studies variations in gene pools
Code is responsible for the phenotype- expression of the gene
Evolution
Changes 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..etc
c) 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
Example of GENE FLOW
•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
.
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.
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 DRIFT
Refers to changes in allele frequencies, usually in small
populations
Occurs 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 the
1860s 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).