Download Ch. 21 Development

Chapter 21
The Genetic Basis
of Development
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• When the primary research goal is to understand
broad biological principles, the organism chosen
for study is called a model organism
• Researchers select model organisms that are
representative of a larger group, suitable for the
questions under investigation, and easy to grow in
the lab
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 21.1: Embryonic development involves
cell division, cell differentiation, and
morphogenesis
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 21-3
Fertilized egg of a frog
Tadpole hatching from egg
Animal development
Cell
movement
Zygote
(fertilized egg)
Eight cells
Gut
Blastula
Gastrula
Adult animal
(cross section) (cross section)
(sea star)
Cell division
Morphogenesis
Observable cell differentiation
Seed
leaves
Plant development
Zygote
(fertilized egg)
Two cells
Shoot
apical
meristem
Root
apical
meristem
Embryo
inside seed
Plant
Concept 21.2: Different cell types result from
differential gene expression in cells with the same DNA
• Differences between cells in a multicellular
organism come almost entirely from gene
expression, not differences in the cells’ genomes
• These differences arise during development, as
regulatory mechanisms turn genes off and on
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Transverse
section of
carrot root
2-mg
fragments
Fragments cultured in nutrient
medium; stirring causes
single cells to
shear off into
liquid.
Single cells
free in
suspension
begin to
divide.
Embryonic
plant develops
from a cultured
single cell.
A single somatic (nonreproductive)
carrot cell developed into a
mature carrot plant. The new
plant was a genetic duplicate
(clone) of the parent plant.
Adult plant
Plantlet is cultured on agar
medium. Later
it is planted
in soil.
Nuclear Transplantation in Animals
• In nuclear transplantation, the nucleus of an
unfertilized egg cell or zygote is replaced with the
nucleus of a differentiated cell
• Experiments with frog embryos have shown that a
transplanted nucleus can often support normal
development of the egg
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Frog embryo
Frog egg cell
Frog tadpole
UV
Fully differentiated
(intestinal) cell
Less differentiated cell
Donor
nucleus
transplanted
Most develop
into tadpoles
Enucleated
egg cell
Donor
nucleus
transplanted
<2% develop
into tadpoles
Reproductive Cloning of Mammals
• In 1997, Scottish researchers announced the birth
of Dolly, a lamb cloned from an adult sheep by
nuclear transplantation from a differentiated
mammary cell
• Dolly’s premature death in 2003, as well as her
arthritis, led to speculation that her cells were
“older” than those of a normal sheep, possibly
reflecting incomplete reprogramming of the
original transplanted nucleus
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 21-7
Mammary
cell donor
Egg cell
donor
Egg cell
from ovary
Cultured
mammary cells
are semistarved,
arresting the cell
cycle and causing
dedifferentiation
Nucleus
removed
Cells fused
Nucleus from
mammary cell
Grown in culture
Early embryo
Implanted in uterus
of a third sheep
Surrogate
mother
https://www.
youtube.co
m/watch?v=
tELZEPcgK
kE
Embryonic
development
Lamb (“Dolly”) genetically identical
to mammary cell donor
• Since 1997, cloning has been demonstrated in
many mammals, including mice, cats, cows,
horses, and pigs
• “Copy Cat” was the first cat cloned, in College
Station, TX at TAMU.
• http://www.youtube.com/watch?v=qIHq2pR6UxA&
feature=related
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Problems Associated with Animal Cloning
• In most nuclear transplantation studies, only a
small percentage of cloned embryos have
developed normally to birth
• Many epigenetic changes, such as acetylation of
histones or methylation of DNA, must be reversed
in the nucleus from a donor animal in order for
genes to be expressed or repressed appropriately
for early stages of development
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Stem Cells of Animals
• A stem cell is a relatively unspecialized cell that
can reproduce itself indefinitely and differentiate
into specialized cells of one or more types
• Stem cells isolated from early embryos at the
blastocyst stage are called embryonic stem cells
• The adult body also has stem cells, which replace
nonreproducing specialized cells
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 21-9
Embryonic stem cells
Totipotent
cells
Adult stem cells
Pluripotent
cells
Cultured
stem cells
Different
culture
conditions
Different
Liver cells
types of
differentiated
cells
Nerve cells
Blood cells
Transcriptional Regulation of Gene Expression
During Development
• Cell determination precedes differentiation and
involves expression of genes for tissue-specific
proteins
• Tissue-specific proteins enable differentiated cells to
carry out their specific tasks
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 21.3: Pattern formation in animals and plants
results from similar genetic and cellular mechanisms
• Pattern formation is the development of a spatial
organization of tissues and organs
• It occurs continually in plants, but it is mostly
limited to embryos and juveniles in animals
• Positional information, the molecular cues that
control pattern formation, tells a cell its location
relative to the body axes and to neighboring cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Life Cycle of Drosophila
• After fertilization, positional information specifies
the body segments in Drosophila
• Positional information triggers the formation of
each segment’s characteristic structures
• Sequential gene expression produces regional
differences in the formation of the segments
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Follicle cell
Egg cell
developing within
Nucleus
ovarian follicle
Egg cell
Nurse
cell
Fertilization
Laying of egg
Fertilized egg
Egg shell
Nucleus
Embryo
Multinucleate
single cell
Early blastoderm
Plasma
membrane
formation
Yolk
Late blastoderm
Body
segments
Cells of
embryo
Segmented
embryo
0.1 mm
Hatching
Larval stages (3)
Pupa
Metamorphosis
Adult fly
Head Thorax
Abdomen
0.5 mm
Dorsal
BODY
AXES
Anterior
Posterior
Ventral
Eye
Leg
Antenna
Wild type
Mutant
Axis Establishment
• Maternal effect genes encode for cytoplasmic
determinants that initially establish the axes of the
body of Drosophila
• These maternal effect genes are also called eggpolarity genes because they control orientation of
the egg and consequently the fly
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• One maternal effect gene, the bicoid gene, affects
the front half of the body
• An embryo whose mother has a mutant bicoid
gene lacks the front half of its body and has
duplicate posterior structures at both ends
• This phenotype suggests that the product of the
mother’s bicoid gene is concentrated at the future
anterior end
• This hypothesis is an example of the gradient
hypothesis, in which gradients of substances
called morphogens establish an embryo’s axes
and other features
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 21-14b
Nurse cells
Egg cell
Developing
egg cell
bicoid mRNA
Bicoid mRNA
in mature
unfertilized
egg
Fertilization
Translation of bicoid mRNA
100 m m
Bicoid protein
in early
embryo
Anterior end
Gradients of bicoid mRNA and Bicoid protein in normal
egg and early embryo
Identity of Body Parts
• The anatomical identity of Drosophila segments is
set by master regulatory genes called homeotic
genes
• Mutations to homeotic genes produce flies with
strange traits, such as legs growing from the head
in place of antennae
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
C. elegans: The Role of Cell Signaling
• The nematode C. elegans is a very useful model
organism for investigating the roles of cell
signaling, induction, and programmed cell death in
development
• Researchers know the entire ancestry of every cell
of an adult C. elegans—the organism’s complete
cell lineage
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Zygote
Time after fertilization (hours)
0
First cell division
Nervous
system,
outer
skin, musculature
Musculature,
gonads
Outer skin,
nervous system
Germ line
(future
gametes)
Musculature
10
Hatching
Intestine
Intestine
Eggs
Vulva
ANTERIOR
POSTERIOR
1.2 mm
Induction
• As early as the four-cell stage in C. elegans, cell
signaling directs daughter cells along the
appropriate pathways, a process called induction
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A number of important concepts apply to C.
elegans and many other animals:
– In the developing embryo, sequential
inductions drive organ formation
– The effect of an inducer can depend on its
concentration
– Inducers produce their effects via signal
transduction pathways, as in adult cells
– The induced cell often responds by activating
genes that establish a pattern of gene activity
characteristic of a particular kind of cell
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Programmed Cell Death (Apoptosis)
• Cell signaling is involved in apoptosis,
programmed cell death
• During apoptosis, a cell shrinks and becomes
lobed (called “blebbing”); the nucleus condenses;
and the DNA is fragmented
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 21-17
2 mm
• In C. elegans, a protein in the outer mitochondrial
membrane is a master regulator of apoptosis
• Research on mammals has revealed a prominent
role for mitochondria in apoptosis
• A built-in cell suicide mechanism is essential to
development in all animals
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The timely activation of apoptosis proteins in some
cells functions during normal development and
growth in both embryos and adult
• In vertebrates, apoptosis is part of normal
development of the nervous system, operation of
the immune system, and morphogenesis of hands
and feet in humans and paws in other mammals
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Interdigital tissue
1 mm
Adult
fruit fly
Fruit fly embryo
(10 hours)
Fly
chromosome
Mouse
chromosomes
Mouse embryo
(12 days)
Adult mouse
Thorax
Thorax
Genital
segments
Abdomen
Abdomen