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Chapter 21: Principles of Development
Freeman, 4 Ed.
Terms in this set (65)
What are the five categories of cellular processes that drive development?
1. cell proliferation
2. programmed cell death
3. cell movement or migration
4. cell differentiation
5. cell-to-cell communication
How is cell proliferation done?
mitosis and cytokinesis
What is apoptosis?
programmed cell death; normal part of development that is carefully regulated
What is an example of apoptosis in development?
the formation of fingers and toes (cells that create webbing are killed off)
What genes code for apoptosis?
What is the major difference between plant and animal cells in development?
animal cells move for normal development to occur; plant cells cannot move because of the cell wall
What is gastrulation?
cells in different parts of an early embryo rearrange themselves into three distinctive types of embryonic tissues which later for specific organs
How do plant cells determine development?
control how the cleavage plane is oriented during cell division and the direction of subsequent cell growth
What is cell differentiation?
a progressive, step-by-step process that a cell follows to become a specialized type of cell
Which animal cells remain undifferentiated?
embryonic stem cells
Where in an animal are partially differentiated cells?
skin, bone marrow (blood), gut, immune system
Why is it beneficial in animals for some cells to remain partially differentiated?
certain systems get beat up and will need constant regeneration; the immune system needs to be able to respond to new pathogens
What does totipotent mean in plants?
"all-powerful," the ability of many plant cells to de-differentiate even after they have specialized
Why are cell-cell signals important?
change patterns of gene expression and are essential for changing cell activity during development
What is differential gene expression?
expression of different genes in different cell types (this is the key to cell differentiation during development)
Do cells express different genes because they contain different genes?
No. They all have the same genes but express different subsets that are activated.
What evidence did scientists use to prove animal cells were genetically equivalent?
transplanted nuclei from diploid frog cells into unfertilized eggs without nuclei resulting in development of normal tadpoles (this was reinforced by nuclear transfer experiments in sheep)
Explain the steps of the sheep cloning experiment.
1. obtain one cell from each sheep
2. culture mammary cell (white-faced sheep) and remove nucleus from egg cell (black-faced sheep).
3. fuse cells
4. nucleus enters egg cell and embryo grows
5. implant embryo in surrogate mother (black-faced sheep)
6. resulting lamb is identical to mammary-cell donor
What are the best cells to use for cloning?
stem cells, which are programmed to make asymmetrical cell divisions
What results from asymmetrical cell division?
1. a daughter cell identical to the parent (i.e. stem cell)
2. a daughter cell that is more differentiated
In adults, where are stem cell populations found?
the gut, skin, immune system, and bone marrow
The process of cellular differentiation does not involve changes in the genetic makeup of cells, except in the _____________________.
What are the different levels that can regulate gene expression?
transcription, RNA processing, translation, and post-translation
What is the fundamental level of control in differential gene expression during development?
In Eukaryotes, how is transcription controlled?
Primarily by the presence of proteins called regulatory transcription factors
What triggers differential gene expression?
1. timing (the current stage of development of the organism)
2. spatial location (where it is in the body of the organism)
What are the axes that determine spatial location?
How do cells know their position in time and space?
by interacting with other cells via cell-cell signaling
What axis indicates your belly and back?
What axis indicates your head and feet?
What is pattern formation?
series of events that determine spatial organization (body axes) of an embryo
What are master regulators?
proteins and protein products that signal to set up major body axes of embryo (they activate network of genes that sends signals with more specific information about spatial location of cells)
What is a segment in terms of body development?
distinct region of animal body that is repeated along its length (i.e. a fly embryo has 3 segments: head, thoracic, and abdominal)
What is a bicoid mutant?
an embryo with two tails and no head region
What is most interesting about a bicoid mutant?
the genotype of the embryo is normal, but the phenotype is clearly abnormal (so we deduce the error must be in the cytoplasm, which comes from the mom)
Where is bycoid produced?
in the mothers egg (either mRNA or protein)
How did researches determine the location of bicoid mRNA in the egg?
by using in situ hybridization
Describe what in situ hybridization is
1. Obtain and label a DNA probe
2. Add probe to specimen (Drosophilia embryo)
3. DNA probe targets mRNA and excess is removed
4. Observe location of probe (radioactive staining)
Describe the formation of the bicoid concentration gradient.
Bicoid protein is made from mRNAs in the anterior end and diffuses away from that end (concentrated in the head region)
What does it mean that bicoid is a transcription regulator?
it allows "made-a-head" genes to switch on, and suppresses "make-a-tail" genes
Why is bicoid physically necessary for transcription?
the bicoid protein causes DNA to fold on itself in a way that promotes transcription (promoter sequence and enhancers)
What are segmentation genes?
genes that organize cells and tissues into distinct segments
What are the three types of segmentation genes?
1. Gap genes
2. Pair-rule genes
3. Segment polarity genes
What do gap genes determine?
early in development, gap genes define general segment positions in anterior, middle, or posterior of body (head-tail axis)
What do pair-rule genes determine?
they demarcate the edges of individual segments
What do segment polarity genes determine?
give positioning information within each segment, delineate boundaries in each segment
What is the relationship between segmentation genes?
they are a regulatory cascade, but they can also act on each other and on themselves
What are homeotic genes?
trigger development of structures appropriate to each type of segment
What is homeosis?
when cells get incorrect information about where they are in the body
What is a homeotic mutant?
when a segment has been transformed onto another segment (it often functions, its just in the wrong place)
What are Hox genes?
expressed in a distinctive pattern along the anterior-posterior axis after segments are established; code for regulatory transcription factors that trigger the production of segment-specific structures (in virtually every animal examined)
What happens when mouse Hox genes are implanted into a fly?
the Hox genes work and the fly develops regularly
What is primarily responsible for the evolution of new body sizes, shapes, and structures?
when mutations alter Hox genes
What is the central kinase of mitosis, that is affected by regulation during cell proliferation?
mitosis-promoting factor (MPF)
What are social controls in cell proliferation?
growth stimulated or inhibited by adjacent cells by receptor proteins in the membrane
How does cell differentiation occur?
altered gene expression (inactivation of some genes and activation of others); transforms structure and function of cell without changing DNA
What enzymes are important in programmed cell death?
protease and DNase
What is the proof that differentiated plant cells are genetically equivalent?
they are totipotent; they de-differentiate
What is the evidence that differentiated animal cells are genetically equivalent?
nuclear transfer (nucleus of a differentiated cell is transplanted into an unfertilized egg)
What is pattern formation?
the establishment of the three-dimensional, spatial organization that initiates many developmental processes (cells receive molecular signals that indicate where they are within the embryo)
What is maternal effect inheritance?
phenotype in the larvae is due only to mother's genotype (i.e. cytoplasmic determinant)
One key example of a gap gene is named...
hunchback (results in embryonic phenotypes similar to those described for bicoid, or, lacking segments in anterior of embryo)
Loss of function in pair-rule genes results in loss of...
ALTERNATING segments in the embryo (these genes form every other segment)
Each of the proteins encoded by the Hox genes contains a...
DNA-binding region that are thought to act as transcription factors
Sonic hedgehog is a transcription factor that controls...
hindlimb development in tetrapods (in snakes this gene shows changes that have altered the functionality of the gene product)
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