Animal Development Chapter 47

Development Preformation – Idea that egg contains a miniature adult that grows only in size during devel. Preformation – Idea that egg contains a miniature adult that grows only in size during devel. Epigenesis – Animal emerges from a formless egg (grows and differentiates). Epigenesis – Animal emerges from a formless egg (grows and differentiates). Microscopy has led to the overwhelming acceptance of epigenesis as the pattern of development in animals. Microscopy has led to the overwhelming acceptance of epigenesis as the pattern of development in animals.

Fertilization Combination of egg nucleus and sperm nucleus. Combination of egg nucleus and sperm nucleus. Activation of egg to begin development of zygote. Activation of egg to begin development of zygote. Internal  Fert. takes place inside body of female (ie: humans) Internal  Fert. takes place inside body of female (ie: humans) External  Fert. takes place in external environment (ie: fish) External  Fert. takes place in external environment (ie: fish)

The Acrosomal Reaction When it contacts the jelly coat of the egg, the sperm releases digestive (hydrolytic) enzymes from acrosome. When it contacts the jelly coat of the egg, the sperm releases digestive (hydrolytic) enzymes from acrosome. Sperm digest jelly coat and membranes fuse. Sperm digest jelly coat and membranes fuse. Sperm nucleus is released into the egg. Sperm nucleus is released into the egg. Fast block to polyspermy  egg depolarizes (Na + in) to prevent double fertilization. Fast block to polyspermy  egg depolarizes (Na + in) to prevent double fertilization.

Cortical Rxn (Slow block to polyspermy) Progressive release of Ca +2 by the egg’s ER causes cortical granules to release enzymes Progressive release of Ca +2 by the egg’s ER causes cortical granules to release enzymes The enzymes in effect harden the egg’s membrane (fertilization membrane) The enzymes in effect harden the egg’s membrane (fertilization membrane) This hard membrane is not penetrable by any more sperm, so only 1 sperm fertilizes the egg This hard membrane is not penetrable by any more sperm, so only 1 sperm fertilizes the egg

Fertilization in Sea Urchin (external)

Egg Activation High levels of Ca 2+ also trigger the egg to increase cellular respiration and protein synthesis High levels of Ca 2+ also trigger the egg to increase cellular respiration and protein synthesis As this takes place, the nuclei of the egg and the sperm fuse with one another As this takes place, the nuclei of the egg and the sperm fuse with one another Diploid zygote nucleus is formed Diploid zygote nucleus is formed Cell division and DNA replication begin as the zygote develops Cell division and DNA replication begin as the zygote develops

Mammal Fertilization (internal) Capacitation  Secretions by female enhance the function of sperm in internally fertilizing mammals Capacitation  Secretions by female enhance the function of sperm in internally fertilizing mammals Zona pellucida recognizes the binding sperm Zona pellucida recognizes the binding sperm Acrosomal and cortical reactions both occur in mammals Acrosomal and cortical reactions both occur in mammals Fast and slow polyspermy blocks similar to sea urchins Fast and slow polyspermy blocks similar to sea urchins

Mammalian Fertilization Entire sperm enters egg and the flagella divide to produce spindle of dividing egg Entire sperm enters egg and the flagella divide to produce spindle of dividing egg Egg and sperm nuclei do not fuse immediately Egg and sperm nuclei do not fuse immediately Share spindle in zygotes initial division. Share spindle in zygotes initial division. Appear first as diploid zygote as daughter of 1 st mitotic division Appear first as diploid zygote as daughter of 1 st mitotic division Sea urchins (external) fused DNA immediately Sea urchins (external) fused DNA immediately

Mammalian Fertilization

Cleavage Rapid cell division that changes the large, single-cell zygote into a large ball of much smaller cells (blastomeres) Rapid cell division that changes the large, single-cell zygote into a large ball of much smaller cells (blastomeres) Cells are smaller because the G 1 and G 2 phases are generally skipped Cells are smaller because the G 1 and G 2 phases are generally skipped Blastomeres each contain different cytoplasmic molecules (determine fate of cells?) Blastomeres each contain different cytoplasmic molecules (determine fate of cells?)

Cleavage in Sea Urchins

Polarity Polarity Most animals (not mammals) exhibit a patterned distribution of materials Most animals (not mammals) exhibit a patterned distribution of materials Vegetal Pole  High yolk Vegetal Pole  High yolk Animal Pole  Low yolk, often anterior of animal Animal Pole  Low yolk, often anterior of animal Cleavage is more rapid in animal pole Cleavage is more rapid in animal pole

Cleavage In sea urchins and frogs, first two divisions vertical, third horizontal In sea urchins and frogs, first two divisions vertical, third horizontal Eight-celled embryo with two tiers of four cells is what continues with cleavage Eight-celled embryo with two tiers of four cells is what continues with cleavage

Cleavage  Morula Stage Cleavage continues and the morula is formed Cleavage continues and the morula is formed The morula is a solid ball of cells The morula is a solid ball of cells

Cleavage  Blastula Stage A fluid filled cavity (blastocoel) forms within the morula A fluid filled cavity (blastocoel) forms within the morula Creates a hollow ball of cells (blastula) Creates a hollow ball of cells (blastula)

Meroblastic/Holoblastic Cleavage Meroblastic Cleavage Birds (plentiful yolk) restrict cleavage to the animal pole of the zygote Birds (plentiful yolk) restrict cleavage to the animal pole of the zygote Holoblastic Cleavage Sea urchins, frogs (less yolk) show complete division of the egg Sea urchins, frogs (less yolk) show complete division of the egg

Gastrulation Development of a three-layered embryo (gastrula) with a primitive gut from the blastula Development of a three-layered embryo (gastrula) with a primitive gut from the blastula Three Embryonic Germ Layers Three Embryonic Germ Layers Ectoderm Ectoderm Endoderm Endoderm Mesoderm Mesoderm

Sea Urchin Gastrulation Begins at the vegetal pole where individual cells enter the blastocoel as mesenchyme cells Begins at the vegetal pole where individual cells enter the blastocoel as mesenchyme cells Rest of cells buckle in to form the archenteron (invagination) Rest of cells buckle in to form the archenteron (invagination) Open end of archenteron will form the anus and the other end the mouth Open end of archenteron will form the anus and the other end the mouth Thus, the archenteron becomes the digestive tube (mouth to anus) Thus, the archenteron becomes the digestive tube (mouth to anus)

Sea Urchin Gastrulation

Organogenesis (differentiation) Ectoderm germ layer gives rise to: Ectoderm germ layer gives rise to: Epidermis of skin, and its derivatives Epidermis of skin, and its derivatives Epithelial lining of the mouth and rectum Epithelial lining of the mouth and rectum Cornea and lens of the eyes Cornea and lens of the eyes The nervous system; adrenal medulla; tooth enamel; epithelium of the pineal and pituitary glands The nervous system; adrenal medulla; tooth enamel; epithelium of the pineal and pituitary glands

Organogenesis Endoderm germ layer becomes: Endoderm germ layer becomes: The epithelial lining of the digestive tract (except the mouth and rectum). The epithelial lining of the digestive tract (except the mouth and rectum). The epithelial lining of the respiratory system. The epithelial lining of the respiratory system. The pancreas; thyroid; parathyroids; thymus; the lining of the urethra, urinary bladder, and reproductive systems The pancreas; thyroid; parathyroids; thymus; the lining of the urethra, urinary bladder, and reproductive systems

Organogenesis Mesoderm germ layer becomes: Mesoderm germ layer becomes: The notochord The notochord The skeletal and muscular systems The skeletal and muscular systems The circulatory and lymphatic systems. The circulatory and lymphatic systems. The excretory system The excretory system The reproductive system (except germ cells) The reproductive system (except germ cells) And the dermis of skin; lining of the body cavity; and adrenal cortex And the dermis of skin; lining of the body cavity; and adrenal cortex

Organogenesis

Amniotic Eggs Allows terrestrial organisms to reproduce in a dry environment Allows terrestrial organisms to reproduce in a dry environment Organisms is kept in a fluid filled environment Organisms is kept in a fluid filled environment Mammals and birds both have amniotic eggs Mammals and birds both have amniotic eggs

Avian Development

Extraembryonic Membranes yolk sac  providing nutrients to the embryo yolk sac  providing nutrients to the embryo Amnion  encloses the embryo in a fluid-filled amniotic sac (protects the embryo from dessication) Amnion  encloses the embryo in a fluid-filled amniotic sac (protects the embryo from dessication) Chorion  cushions the embryo Chorion  cushions the embryo allantois  disposal sac for uric acid (urine) allantois  disposal sac for uric acid (urine)

Amniotic Egg (Bird/Reptile)

Human Amniotic Development Human embryos develop in amniotic eggs the way birds and reptiles do, except they are implanted in the uterus, not externally developing Human embryos develop in amniotic eggs the way birds and reptiles do, except they are implanted in the uterus, not externally developing There is more exchange of materials b/t mother and offspring (blood cells for immunity, nutrients, waste) There is more exchange of materials b/t mother and offspring (blood cells for immunity, nutrients, waste) ie: placental mammals (humans) ie: placental mammals (humans) ie: marsupial mammals (kangaroos) ie: marsupial mammals (kangaroos)