“The very foundation of biology and the key to understanding our human origins…”
-R. Hutton, WGBH
Developmental biologists are discovering remarkable similarities in the mechanisms that shape diverse organisms.
Clear connections between genes and development made by studying selected “model organisms”
Through a succession of mitotic cell divisions, the zygote gives rise to a large number of cells
In cell differentiation, cells become specialized in structure and function
Morphogenesis encompasses the processes that give shape to the organism and its various parts
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Animal development
Zygote(fertilized egg)
Eight cells Blastula(cross section)
Gastrula(cross section)
Adult animal(sea star)
Cellmovement
Gut
Cell division
Morphogenesis
Observable cell differentiation
Seedleaves
Shootapicalmeristem
Rootapicalmeristem
PlantEmbryoinside seed
Two cellsZygote(fertilized egg)
Plant development
Differences between cells in a multicellular organism come almost entirely from gene expression◦ regulatory mechanisms turn genes off and on◦ nearly all cells of an organism have genomic
equivalence ie: the same genome
A typical cell expresses 20% of its genes at any given time.
1.5% of DNA codes for protein, less codes for rRNA and tRNA the rest is NON coding.
Most control of gene expression happens during transcription = lead by outside signals
Gene ExpressionGene Expression
MOST gene expression control happens in TRANSCRIPTION
DNA unpacking is needed to express the genes in this (unwound) region
DNA unpacking requires:◦ Histone acetylation◦ DNA demethylation
DNA unpackingDNA unpacking
Activator: a protein that binds to an enhancer and stimulates transcription of a gene
Enhancer: a DNA code upstream from a gene that regulates the expression of that gene.
Transcription factorsTranscription factors
Plants Animals
totipotent cell - one that can generate a complete new organism
A single somatic carrot cell developed into a
mature carrot plant. The new plant was a genetic duplicate (clone) of the parent plant.
nuclear transplantation the nucleus of an unfertilized egg cell or zygote is replaced with the nucleus of a differentiated cell◦ frog embryos◦ Dolly the Sheep◦ “Copy Cat”
Relatively unspecialized cell that can reproduce itself indefinitely and differentiate into specialized cells of one or more types
Embryonic stem cells are totipotent, able to differentiate into all cell types
Adult stem cells are pluripotent, able to give rise to multiple but not all cell types
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Embryonic stem cells Adult stem cells
Pluripotentcells
Totipotentcells
Culturedstem cells
Differentcultureconditions
Differenttypes ofdifferentiatedcells
Liver cells Nerve cells Blood cells
• Cell differentiation involves expression of genes for tissue-specific proteins
• Tissue-specific proteins enable differentiated cells to carry out their specific tasks
• Pattern formation is the development of a spatial organization of tissues and organs
Apoptosis: programmed cell death (how humans lose the fetal tail
Comparative Biochemistry◦ An identical or very similar nucleotide sequence has
been discovered in the homeotic genes of both vertebrates and invertebrates
◦ Hox genes or homeobox: control identity of body parts
◦ Related genetic sequences have been found in regulatory genes of yeasts, plants, and even prokaryotes
In both plants and animals, development relies on a cascade of transcriptional regulators turning genes on or off
Similarities reflect the common ancestry of life on Earth◦ In biological mechanisms to establish body
patterns
Differences have created the diversity of living organisms◦ exact genes directing development may differ
Change over time in the genetic composition of a population
The gradual appearance of all biological diversity
Evolution explains life’s unity and diversity
Effects biology at every level, from molecules to ecosystems!
“Darwin Day is an international celebration of science and humanity “
“Charles Darwin -- the man who first described biological evolution via natural selection with scientific rigor”
http://www.darwinday.org/
www.omniscopic.com
◦ Many current species are descendants of ancestral species
◦ Natural selection is a mechanism for this evolutionary process cause of adaptive
evolution
www.personal.psu.edu
It was generally believed that species had remained unchanged since their creation
Aristotle viewed species as fixed and unchanging
Old Testament holds that species were individually designed by God and therefore perfect
Linnaeus - the Creator had designed each species for a specific purpose
http://www.genetologisch-onderzoek.nl/wp-content/
image_upload/darwincartoon.jpg
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NORTHAMERICA
SOUTHAMERICA
AFRICA
EUROPE
AUSTRALIA
PACIFICOCEAN
ATLANTICOCEAN
England
Cape ofGood Hope
Cape Horn
Tierra del Fuego
GalápagosIslands
Darwin in 1840,after his return
HMS Beagle in port
Equator
Tasmania
NewZealand
An
des
All organisms are related through descent from an ancestor that lived in the remote past
history of life is like a tree with branches representing life’s diversity
Overproduction of offspring
Variation in organisms
Competition for resources and avoid prey
Survival to reproduction
differential success in reproduction individuals that vary in heritable traits
Produces differing reproductive success in a particular environment
If an environment changes over time, natural selection may result in adaptation to these new conditions
Mutation (primary source in prokaryotes) Sexual Reproduction
◦ Random mating◦ Crossing over
Transposable elements: segments of DNA that can move around within genome.◦ Transposons: move by means of DNA◦ Retrotransposons: move by means of RNA
Genetic Variability Genetic Variability
A flower mantidin Malaysia
A stick mantidin Africa
Beware of Natural Selection
The evolutionary impact of natural selection is only apparent in the changes in a population of organisms over time.
It is the population, not the individual, that evolves
Evolution is compromise not perfection.
Bacterial and Viral Drug Resistance
Homology
◦ use of drugs to combat HIV selects for viruses resistant to these drugs
◦ Increasing numbers of antibiotic resistant bacterial outbreaks like MRSA
◦ Homologous structures-variation on common structural theme
◦ Comparative Embryology-similarities not seen at adult level
◦ Vestigial organs-appendix
◦ Molecular homologies-genes shared among organisms Insulin, Growth Hormone
Bottle Neck Effect Deminishing of a
population due to natural disaster
Reducing genetic variation
Founder Effect Individuals in a
population become isolated from others◦ Develops different gene
pool Blue People! Colonists form England
Genetic Drift “Unpredictability from
one generation to the next◦ based on allele
frequencies◦ Based on chance◦ Based on gene pool
Disruptive Selection
Directional Selection Occurs when
population’s environment changes’
Or members migrate Favors non-average
individuals
Stabilizing Selection Favors members in
middle of scale. Usually stable
environment
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Percent of Amino Acids That AreIdentical to the Amino Acids in aHuman Hemoglobin Polypeptide
100%
95%
87%
69%
54%
14%
Rhesus monkey
Species
Human
Mouse
Chicken
Frog
Lamprey
Biogeography
geographic distribution of species
similar mammals that have adapted to similar environments have evolved independently from different ancestors
Fossil Record
succession of forms observed in the fossil record is
Rock layers reveal hierarchy of ancestry
evolutionary transitions leave signs