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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
Two Types of Cells
Somatic cells
• The vast majority of cells in our bodies
• Reproduce through mitosis
Sex Cells (gametes)
• Only found in ovaries and testes
• Reproduce through meiosis
Two Types of Cell Division
Mitosis
• Occurs in somatic cells
• Produces 2 daughter cells• Genetically identical• diploid
Meiosis
• Occurs in sex cells (gametes)
• Produces 4 daughter cells• Genetically unique• haploid
Mitosis
• Asexual reproduction
• Occurs in somatic cells
• Produces 2 genetically identical diploid daughter cells
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
• Autosomes• Pairs 1-22
• Are homologous• same length• same sequence of genes (may be
different alleles)
Human karyotype
• Sex chromosomes• Pair 23
• X & YX longer than Y
• XX – homologous• XY – partially
homologous
and genes contain… Deoxyribonucleic Acid
• Present in all living organisms
• Amount varies from organism to organism
• Species can read each others’ DNA
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
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 process1) transcription2) translation
• The process whereby the DNA message is converted into a protein product
for more information…
Web siteshttp://www.dnalc.org/resources/
http://en.wikipedia.org/wiki/
http://www.johnkyrk.com/
http://www.youtube.com/
Key words• DNA replication
• Protein synthesis
• DNA translation
• Transcription
How Should We Describe Populations?
Monogenic Traits
• Qualitative
• Discontinuous graph
Polygenic Traits
• Quantitative
• 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 exhibitsvariation
for that trait
andvariation
is what makesevolutionpossible
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 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
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
•Natural selection
•Mutation
•Migration
•Assortative mating• Positive• negative
•Genetic drift
Natural Selection
• Do blondes have more fun (and more early onset skin cancer)?
• Is it better to be redder?
• Hereditary diseases, anyone?
• Other possibilities?
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
• phenotypically similar organisms
• increases homozygosity
• decreases variation
Negative Assortative Mating
• phenotypically dissimilar organisms
• increases heterozygosity
• increases variation
A genetic bottleneck reduces a population temporarily to very low levels, removing much of its genetic diversity.
In 1790, 9 Bounty mutineers plus 18 Tahitians (six men, 11 women and a baby)
fled to Pitcairn Island