Download 4 - On Cells, DNA, Proteins, and Populations

Biological Anthropology
On Cells, DNA, Proteins, and Populations
Cell Theory
• A set of explanatory principles used to understand cells
• Cells are the smallest unit of life
• Consist of smaller (non-alive) parts: organelles
A Cell
Two Types of Cells
Somatic cells
Sex Cells (gametes)
• The vast majority of cells in our
bodies
• Only found in ovaries and testes
• Reproduce through mitosis
• Reproduce through meiosis
Two Types of Cell Division
Mitosis
Meiosis
• Occurs in somatic cells
• Occurs in sex cells (gametes)
• Produces 2 daughter cells
• Produces 4 daughter cells
• Genetically identical
• diploid
• Genetically unique
• haploid
Mitosis
• Asexual reproduction
• Occurs in somatic cells
• Produces 2 genetically
identical diploid
daughter cells
Meiosis
• Occurs in sex cells
(gametes)
• Produces 4 daughter
cells
• Genetically unique
• haploid
Crossing-Over
6
wet
A
5
dry
# of fingers 6
cerumen dry
O ABO group
A
5
wet
O
Cell Division
Mitosis
Meiosis
Karyotype
• Species-specific set of chromosomes
• Differs from species to species in terms of
• The number of chromosomes
• The sequences of genes contained in the chromosomes
Human karyotype
• 46 chromosomes
• Arranged in
23 pairs
• 1 set from
each parent
Human karyotype
• Autosomes
• Pairs 1-22
• Are homologous
• same length
• same sequence of genes (may be
different alleles)
Human karyotype
• Sex chromosomes
• Pair 23
•X & Y
X longer than Y
• XX – homologous
• XY – partially
homologous
So what’s in a chromosome?
Let’s take a look!
A chromosome contains genes
and genes contain…
Deoxyribonucleic Acid
• Present in all living
organisms
• Amount varies from
organism to organism
• Species can read each
others’ DNA
DNA
• Sugar-phosphate
backbone”
• Bases are “rungs”
adenine = thymine
cytosine = guanine
Genome
the total DNA/genes of a species
• Homo sapiens
• app. 3,000,000,000 DNA bases
• 35,000 – 40,000 genes
• Honeybee – 300,000,000 DNA bases
• Fruit fly – 13,600 genes
• Bacteria – a few hundred to a few thousand genes
DNA Replication
• Produces two identical
strands from one original
strand
• Each side of the original
is a template for making
a new copy of its
complement
The Three Problems
1.
How is the variation present within a species at any time affected by
the environment?
Darwin
2.
How is variation passed on from one generation to the next?
Mendel
3.
Where does variation come from?
Watson & Crick
But what are genes used for?
Protein Synthesis
• A two stage process
• Transcription
• Translation
• Our players:
• Messenger RNA (mRNA) – the locks
• Transfer RNA (tRNA) – the keys
• Ribosome (“locksmith)
• Amino Acids
Protein Synthesis
•
1: Transcription
messenger RNA (mRNA) copy of gene is made
•
mRNA copy leaves nucleus and goes to cytoplasm
Protein Synthesis
2: Translation
• mRNA copy is “read” by ribosomes
• Ribosomes match tRNA to codons on mRNA
Proteins: the End Result
• One gene codes for
one protein
• Differences between
individuals due (in
part) to differences
in their proteins
Protein Synthesis,
once again…
• A two stage process
1) transcription
2) translation
• The process whereby the DNA message is converted into a protein
product
for more information…
Web sites
http://www.dnalc.org/resources/
Key words
• DNA replication
http://en.wikipedia.org/wiki/
• Protein synthesis
http://www.johnkyrk.com/
• DNA translation
http://www.youtube.com/
• Transcription
and now let’s turn to…
Population Genetics
Population
• A (potentially) interbreeding
group of organisms
• (usually) a subset of a species
“Populations” Differ
How Should We Describe Populations?
Monogenic Traits
Polygenic Traits
• Qualitative
• Quantitative
• Discontinuous graph
• Continuous graph
Use Polygenic Traits?
• Advantage: often easily observable
• Disadvantage: can change over an individual’s life time
• Poorly suited for population studies
Racism
• A social/cultural phenomenon
• Attempts to distinguish between human populations on the basis of
polygenic traits
• Used to justify hierarchies within society
• Is not based on scientifically valid criteria
Use Monogenic Traits!
• Disadvantage: not always easily observable
• Advantage: do not change over an individual’s life
time
• Useful in the study of populations
• Genetic Markers = monogenic traits in which the
genotype is known
Genetic polymorphism
When two or more phenotypes exist within a
population
that means that the population exhibits
variation
for that trait
and
variation
is what makes
evolution
possible
Adaptation
a trait that increases an organism’s reproductive success
What adaptation is being measured here?
How might this adaptation increase an individual’s reproductive success?
Adaptation
(a classic example)
The wing color of the Peppered Moth is a monogenic trait
Adaptation
produced by natural selection in the context of a particular
environment
A light variant mating with a
dark variant
Light and dark variants on light
and dark backgrounds
Adaptation
produced by natural selection in the context of a particular
environment
Smokestacks during the
Industrial Revolution
Evolution defined
drum roll please…
A change in allele frequency from one
generation to another
This means that…
the unit of selection is the individual
while
the unit of evolution is the population
Population Genetics
• Studies how evolution occurs in populations of organisms
• Population – a (geographically localized) group of individuals in a
species that share a common gene pool and tend to find their mates
within this group
What are the factors that could influence the
evolution of our population?
•Founder’s effect
•Assortative mating
• Positive
•Natural selection
•Mutation
•Migration
• negative
•Genetic drift
Founder’s effect
• How well would we represent
the population from which we
are derived?
• SoCal!
Natural Selection
• Do blondes have more fun (and
more early onset skin cancer)?
• Is it better to be redder?
• Hereditary diseases, anyone?
• Other possibilities?
Mutation
• Random mutations
• Heightened mutation rates?
• Cosmic rays?
Uranium ore
Migration
• Do some people leave?
• Do others arrive?
• Did some “visit”?
• Gene flow vs. migration
Hypothesized migration pattern of the
Pacific Islands
Assortative Mating
Positive Assortative Mating
Negative Assortative Mating
• phenotypically similar
organisms
• phenotypically dissimilar
organisms
• increases homozygosity
• increases heterozygosity
• decreases variation
• increases variation
Genetic Drift
the random factor, or “joker in the deck”
A genetic bottleneck reduces a population temporarily to very low levels, removing much of its
genetic diversity.
Mutiny on the Bounty
by Robert Dodd (artist & engraver); 2 Oct., 1790
In 1790, 9 Bounty mutineers plus 18 Tahitians (six
men, 11 women and a baby)
fled to Pitcairn Island
The Pitcairn
Islanders today
app. 60 people
(the smallest democracy in
the world!)