an organism’s development is planned by a genetic program involving the genome of the zygote and...
TRANSCRIPT
Animal Development Chapter 47
Chloe Vickers AP Biology
A Body-Building Plan
An organism’s development is planned by a genetic program involving the genome of the zygote and the molecules placed in the egg by the mother› These molecules are called cytoplasmic determinants › As the zygote divides, differences occur between early
embryonic cells due to the uneven distribution of cytoplasmic determinants and to signals from neighboring cells
› The process of cell specialization in structure and function is called cell differentiation
› Development involves morphogenesis , the process by which an organism takes shape and the differentiated cells occupy their appropriate locations
Fertilization
The main function of fertilization is the combining of haploid sets of chromosomes from two individuals into a single diploid cell › Contact of the sperm with the egg’s surface starts metabolic
reactions within the egg and “activating” it The acrosomol reaction begins when a specialized vesicle at
the tip of the sperm, called the acrosome, discharges hydrolytic enzymes
Egg activation is the outcome of the sharp rise of Ca2+
concentration in the egg’s cytosol, as well as the binding and fusion of sperm
Unfertilized eggs of many species can be artificially activated by the injection of Ca2+
Fertilization in mammals is mostly internal, which causes an increase in sperm motility
Cleavage
During cleavage, cells carry out the S and M phases of the cell cycle. Cleavage divides the cytoplasm of a zygote into smaller cells called blastomeres › Eggs and zygotes have a definite polarity which have a specific pattern
that needs to be followed› The polarity is defined by the uneven distribution of substances in the
cytoplasm, including cytoplasmic determinants and yolk (stored nutrients)
The distribution of yolk is a key factor influencing the pattern of cleavage. It’s often concentrated toward one pole of the egg, called the vegetal pole; the yolk concentration decreases toward the opposite pole, the animal pole
Establishment of the three body axes occurs early in development. The animal and vegetal hemispheres of the zygote can be distinguished by color (animal is gray and vegetal is yellow)
Cortical rotation is when the plasma membrane and associated cortex rotate with respect to the inner cytoplasm
Gastrulation
Is the morphongenetic process in which cells take up new locations that will allow the formation of tissues and organs. The result is that some cells at or near the surface of the blastula move to a new interior location, and three cell layers are established
http://www.youtube.com/watch?v=f0tZUkTaGYw
Organogenesis
During organogenesis, various regions of the three embryonic germ layers develop into the rudiments of organs › Involves localized shape changes in both
tissues and individual cells
Cytoskeleton
Is a dynamic structure that maintains cell shape, protects the cell, enables cellular motion (using structures such as flagella, cilia, and lamellipodia), and plays important roles in both intracellular transport and cellular division › Cell adhesion molecules (CAMs) are a
key group of proteins that contribute to cell migration and stable migration and stable tissue structure
Fate Mapping
Fate maps of embryos have shown that specific regions of the zygote or blastula develop into specific parts of older embryos
Cellular Asymmetries
In nonamniotes, unevenly distributed cytoplasmic determinants in the egg are important in establishing the body axes and in setting up differences between the blastomeres resulting from cleavage of the zygote
Cells that receive different cytoplasmic determinants result in different outcomes
Cell Fate Determination and Pattern Formation
Cells in a developing embryo receive and respond to positional information that differs with location › This information is in the form of signaling
molecules hidden by cells in special “organizer” regions of the embryo The signaling molecules influence gene
expression in the cells that receive them