Lecture #9Date______

Lecture #9Lecture #9 Date______Date______

Chapter 21Chapter 21~~ The Genetic Basis The Genetic Basis of Developmentof Development

From fertilized egg to From fertilized egg to multicellular organismmulticellular organism

Cell Division:Cell Division:increase in cell increase in cell

numbernumber Differentiation:Differentiation: cells cells

becoming becoming specialized in structure specialized in structure and and functionfunction

Morphogenesis;Morphogenesis;physical processes physical processes giving an organism giving an organism shapeshape

Morphogenesis: plants vs. animalsMorphogenesis: plants vs. animals AnimalsAnimals:: movements of cells and tissues are movements of cells and tissues are

necessary for 3-D form of the necessary for 3-D form of the organismorganism

ongoing development in adults ongoing development in adults restricted to differentiation of cells restricted to differentiation of cells continually replenished throughout continually replenished throughout lifetimelifetime

PlantsPlants:: morphogenesis and growth of overall morphogenesis and growth of overall

size occur throughout lifetime of size occur throughout lifetime of plant; apical meristems (perpetually plant; apical meristems (perpetually embryonic regions), responsible for embryonic regions), responsible for plant’s continual growthplant’s continual growth

Embryonic developmentEmbryonic development

Differential gene expressionDifferential gene expression Differences between cells come from Differences between cells come from

differences in gene expressiondifferences in gene expression (genes (genes turned on or off), turned on or off), not from differing not from differing genomesgenomes..

Evidence:Evidence: 1- 1- Genomic equivalenceGenomic equivalence:: all the all the

cells of an organism have the same cells of an organism have the same genesgenes

2- Totipotency:2- Totipotency: cells that can retain the cells that can retain the zygote’s potential to form all parts of the zygote’s potential to form all parts of the mature organism (plant cells; cloning)mature organism (plant cells; cloning)

3- Determination3- Determination: restriction of : restriction of developmental potential causing the developmental potential causing the possible fate of each cell to become possible fate of each cell to become more limited as the embryomore limited as the embryo develops; develops; noted by the appearance of mRNAnoted by the appearance of mRNA

Determination--->DifferentiationDetermination--->Differentiation

DeterminationDetermination: as the embryo : as the embryo develops the possible fate of each develops the possible fate of each cell becomes more limitedcell becomes more limited

DifferentiationDifferentiation: specialization of : specialization of cells dependent on the control of cells dependent on the control of gene expressiongene expression

InductionInduction: the ability of one group : the ability of one group of embryonic cells to influence the of embryonic cells to influence the development of another; development of another; cytoplasmic determinants that cytoplasmic determinants that regulate gene expressionregulate gene expression

Homeotic genesHomeotic genes: genes that : genes that control the overall body plan of control the overall body plan of animals by controlling the animals by controlling the developmental fate of groups of developmental fate of groups of cellscells

Genetic cell deathGenetic cell death ApoptosisApoptosis programmed programmed

cell death (“suicide genes”)cell death (“suicide genes”) 1. Programmed cell death is as 1. Programmed cell death is as

needed for proper development as needed for proper development as mitosis is. mitosis is.

Ex:Ex: Reabsorption of the tadpole tail; Reabsorption of the tadpole tail; formation of the fingers and toes of formation of the fingers and toes of the fetus requires the removal of the the fetus requires the removal of the tissue between them; sloughing off of tissue between them; sloughing off of the endometrium at the start of the endometrium at the start of menstruation; formation of the proper menstruation; formation of the proper connections (synapses) between connections (synapses) between neurons in the brain requires that neurons in the brain requires that surplus cells be eliminated.surplus cells be eliminated.

Apoptosis, Pt. IIApoptosis, Pt. II 2. Programmed cell death is needed to destroy cells 2. Programmed cell death is needed to destroy cells

that represent a threat to the integrity of the that represent a threat to the integrity of the organism. organism.

Ex: Cells infected with viruses; waning cells of the Ex: Cells infected with viruses; waning cells of the immune system; cells with DNA damage; cancer cells immune system; cells with DNA damage; cancer cells

Concept Check Question #1:Concept Check Question #1:

Why can’t a single embryonic stem Why can’t a single embryonic stem cell develop into an embryo?cell develop into an embryo?– Cytoplasmic determinants:Cytoplasmic determinants:

Substances supplied by the mother that Substances supplied by the mother that influence the course of early developmentinfluence the course of early development

Cytoplasmic Determinants:Cytoplasmic Determinants: Substances supplied by the mother that influence Substances supplied by the mother that influence

the course of early developmentthe course of early development

– Egg cytoplasm contains RNA and proteins Egg cytoplasm contains RNA and proteins encoded by the mothers DNAencoded by the mothers DNA

– Heterogeneous unfertilized eggHeterogeneous unfertilized egg Helps determine developmental fate by regulating Helps determine developmental fate by regulating

expression of the cell’s genesexpression of the cell’s genes

Determination: Determination:

as the embryo develops the as the embryo develops the possible fate of each cell becomes possible fate of each cell becomes more limitedmore limited

Concept Check Question #2:Concept Check Question #2:

If you clone a carrot, will all the If you clone a carrot, will all the progeny plants look identical?progeny plants look identical?– No, due to environmental differencesNo, due to environmental differences– Environment also plays a role in the Environment also plays a role in the

developmental fatedevelopmental fate

Totipotency in plants: Totipotency in plants:

Mature cells in plants can dedifferentiate and give rise to all the specialized cell types of the mature organism Changes in DNA are not

irreversible Any plant cell has this ability

Pluripotency of Animal Cells: Pluripotency of Animal Cells:

Adult stem cells are able to give rise to Adult stem cells are able to give rise to multiple cell types but not allmultiple cell types but not all– Stem cell: relatively unspecialized cell that Stem cell: relatively unspecialized cell that

can both reproduce itself indefinitely and can both reproduce itself indefinitely and under appropriate conditions differentiate under appropriate conditions differentiate into specialized cells on one or more types. into specialized cells on one or more types.

Therapeutic Cloning:Therapeutic Cloning:

Using embryonic stem cells to treat Using embryonic stem cells to treat diseasedisease– Harvested from the human blastocystHarvested from the human blastocyst– Reproduce indefinitely into various Reproduce indefinitely into various

specialized cells including sperm and egg specialized cells including sperm and egg cellscells

Concept Check Question #3: Concept Check Question #3:

The signal molecules released by an The signal molecules released by an embryonic cell can induce changes embryonic cell can induce changes in a neighboring cell without entering in a neighboring cell without entering the cell. How? the cell. How?

Signal transduction pathwaySignal transduction pathway Binding to a surface receptor and Binding to a surface receptor and

triggering a transduction pathwaytriggering a transduction pathway

Induction: Induction:

signal molecules causing changes in target cells

Signals from surrounding embryonic cells can imping on a cell.

Signal molecules:Signal molecules:

Signal molecules are proteins produced by the growing embryo– These molecules send a cell down a

specific developmental pathway by causing change in its gene expression that results in observable cellular changes.