AP biology: 21/47 evodevo Flashcards
embryos have been studied since…
In 1901 Hans Spemann used baby hair ligature to induce twins in early frog embryos
Ross Harrison
1918- self regulation
Early embryonic tissue has “morphogenetic fields” that regulate their own differentiation
The Organizer Experiment
1924 Speman and Mangold
Discovered embryonic induction and received the Nobel Prize in 1935
Homeotic transformations
Carl Lewis 1946
Bithorax = patterned gene discovered by Morgan
determined the pattern of thorax and abdomen of fruit flies
Mutations caused transformations of one body region/ segment into another
Proceed in order from anterior to posterior (front to back)
Homeobox
1983- Garber and Gehring – Anntennapedia
Gene that can transform an antenna into a leg
Homeobox- short sequence in all sequence genes – 180 bases long or 60 amino acids
Shortened to HOX genes
Connect all bilateral animals – genes have duplicated and changed with time
Human embryo takes how long to show distinctive features
6-8 weeks
Zygote to embryo (5)
Zygote formation due to sperm and egg fusion
Cortical reaction- increase in Ca++ ions block polyspermy and increases cellular respiration
Cleavage- zygote divides into smaller cells ( blastomeres)
16- 32 cell stage- the morula
Hollow ball= blastula( at least 120 cells)
Gastrulation
Gastrulation rearranges the cells of a blastula into a three-layered embryo, called a gastrula, which has a primitive gut
ectoderm
germ layer
forms the outer layer: becomes nervous system, outer epidermis, cornea and lens of eye, and pituitary glands
endoderm
lines the digestive tract along with skeletal, muscular, excretory, ciculatory, lymphatic, and reproductive systems
mesoderm
partly fills the space between the endoderm and ectoderm and becomes the epithelial lining of respiratory and excretory systems, the liver, pancreas, thyroid and parathyroid glands
cell divisions
The zygote gives rise to a large number of cells
cell differentiation
Cells become specialized in structure and function
morphogenesis
encompasses the processes
That give shape to the organism and its various parts
Genomic equivalence
All nucleated cells in an organism have the exact same genome or same DNA.
Differences between cells in a multicellular organism
Due almost entirely from differences in gene expression.
Stem cell is a relatively unspecialized cell because
Can reproduce itself indefinitely
Can differentiate into specialized cells of one or more types, given appropriate conditions
totipotent cell
Is one capable of generating a complete new organism
pluripotent cell
can become many different types but not all
cloning
Is using one or more somatic/ body cells from a multicellular organism to make another genetically identical individual
Experiments with frog embryos…
Have shown that a transplanted nucleus can often support normal development of the egg
John Gurdon
Differentiation
1962: repeated experiment BUT
Removed frog egg nucleus and replaced with diploid nucleus of mature intestinal cell
Fully mature tadpole/ frog resulted
Reproductive cloning of mammals
In 1997, Scottish researchers
Cloned a lamb from an adult sheep by nuclear transplantation
In nuclear transplantation
The nucleus of an unfertilized egg cell or zygote is replaced with the nucleus of a differentiated cell
first cat ever cloned
“Copy cat”
Problems associated with animal cloning
In most nuclear transplantation studies performed thus far
Only a small percentage of cloned embryos develop normally to birth
Defects may result ( heart disease etc)
Over methylation of “donor DNA” which may interfere with normal development if genes are turned off
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
Stem cells can be isolated
From early embryos at the blastocyst stage
Shinya Yamanaka 2006
Created iPSC ( induced pluripotent stem cells) Introduced 4 genes to reprogram adult skin cell into neurons and intestinal cells Since then: created egg cells which are totipotent
Cytoplasmic Determinants and Cell-Cell Signals in Cell Differentiation
Maternal substances that influence early development are called cytoplasmic determinants
These substances regulate expression of genes that affect the cell’s developmental fate
Induction
The other important source of developmental information is the environment around the cell, especially signals from nearby embryonic cells
In the process called induction, signal molecules from embryonic cells cause transcriptional changes in nearby target cells
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
HOX genes early on determine
Role of Apoptosis in vertebrates
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
Apoptosis process
During apoptosis, a cell shrinks and becomes lobed (called “blebbing”); the nucleus condenses; and the DNA is fragmented
The timely activation of apoptosis proteins in some cells functions during normal development and growth in both embryos and adult
