Embryonic Development of Animals Russell Chapter 50 AP Biology/ Rhodes

Study of embryology began with Aristotle “formation of the embryo” Development from single egg cell to multicellular animal Growth Development of all organ systems Following directions of DNA 3D Morphology = the form or shape of an organism completed using mitosis Cell differentiation = changes in gene expression set cells on a path to establish specialized structures and functions. Morphogenesis = generation of 3D body form

50.1 Mechanisms of Embryo Development Egg + sperm = zygote; now a free living organism mRNA and proteins in egg are cytoplasmic determinants of growth; mRNA of egg directs activity until zygote DNA becomes active Lots of ribosomes, mitochondria and tubulin, usually pigment Development happens on three axes; anterior posterior, dorsal ventral and left right YOLK = nutrients; although placental mammals have relatively little yolk Unevenly placed causing polarity Slower division at yolk region – Vegetal pole; faster divisions, gut and posterior regions (yolk end) animal pole; surface and anterior structures – has egg nucleus

Early Development Cleavage Gastrulation Organogenesis Lots of mitosis No change in size or volume Many little cells called blastomeres in a frog 12 cleavages lead to 4000 cells Gastrulation Now form three major tissue layers or regions Cells divide, migrate and rearrange Organogenesis Develops all major organ systems and body organization specific to the species

CLEAVAGE Morula Blastula Gastrula Solid ball of blastomeres Eventually hollow ball called blastula that surrounds Fluid filled cavity called blastocoel [Coelom and coelomate and acoelomates] Extensive cell rearranging Gastrula Surface cells move toward center (pocket) in process called gastrulation that forms The gastrula or animals “belly” Three layers of cells are created “germ layers” [germ = germinate or give rise] Ectoderm = outer layers; skin/ hair/ feathers/ nerves/ lining of mouth/ glands Table 50.1 Endoderm= inner layers; linings of all organs Mesoderm= middle layers; muscle and bones, blood vessels DIFFERENTIATION

Gastrulation  Embryo Changes in biochemistry, structure, function Totipotent - capable of producing all kinds of cells Pluripotent – create most types of adult cells Multipotent – cells with particular funtions Cells still have ALL the DNA, just after specialization (differentiation) they only have access to parts of the genome that they need/use

Development Processes 1. Mitosis 2. Cell migrations 3. Cell adhesions – make and break connections between cells  tissues 4. Induction – influences by surrounding cells 5. Determination – must become a cell type because of induction 6. Differentiation – cell specific development (structures and functions) 7. Apoptosis – programmed cell death…. Between fingers

50.3 Gastrulation  Organogenesis Pg. 1126 Neural tube formation Neurulation Notochord Neural plate Neural tube Somites