“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