Animal Development

Chapter 47

Keonna & Brianna

Fertilization, cleavage, Gastrulation,& Organogenesis Main function of fertilization is the combining of

haploid sets of chromosomes from two individuals into a single diploid cell, the Zygote.

Acrosomal reaction- The discharge of hydrolytic enzymes that come from a vesicle in the tip of the sperm, the acrosome, occurs when the sperm approaches or touches the egg.

Cortical reaction – Excocytosis of enzymes and other macromolecules from cortical granules in the egg cytoplasm during fertilization, leading to the formation of fertilization envelope.

After fertilization is complete, rapid cell divison occurs. This stage called cleavage, the cells carry out the S and M phases of the cell cycle.

The acrosomal & cortical reactions during sea urchin fertilization.

Fertilization, cleavage, Gastrulation,& Organogenesis After cleavage, the rate of cell division slows

down, and undergo a process called gasturlation. This process takes up locations that will later for organs and tissues.

Fertilization, cleavage, Gastrulation,& Organogenesis Organogenesis is the process in which organ

rudiments development from, the 3 germ layers after gastrulation

Developmental adaptations of amniotes

Mammalian development

Require aqueous environment for development.

Reptiles and mammals in eggs or the uterus are surrounded by a fluid within are called amniotes.

Chorin, amnion, yolk sac, and the allantois make up the “life-support system” for further embryonic development

Fertilization occurs in the oviduct, then continues as it completes its journey to the uterus.

When embryonic cells separate , causes twins

Allantois in mammals is incooperated in the umbilical cord.

There it forms blood vessels that transport Oxygen/nutrients from the placenta and gets rid of harmful waste and carbon dioxide.

Morphogenesis in animals involves specific changes in cell shape,position,and adhesion Changes of the cells usually involve the

reorganization of the cytoskeleton. Cytoskeleton drives cell migration.

Cell adhesion molecules- cell-surface molecule that bonds to CAM’s on other cells results in cell-to-cell attachments contribute contributing to strong tissues attachments.

Credit: 8th edition biology: Cambell.Reece

Developmental Fate of Cells During early cleavage

divisions have to differentiate themselves. Initial differences result

from uneven distribution of cytoplasmic determinants

Induction - Interactions among embryonic cells influence their fate by changing gene expression

Fate maps provide a territorial diagram of embryonic development Fate maps also trace the

ancestry of each cell In many species that

have cytoplasmic determinants only the zygote is totipotent Totipotent – capable of

turning into all the different cell types in that species

Developmental Fate of Cells Inductive signals play

an important role in: pattern formation – the

arrangement of organs and tissues

Positional information – tells a cell where it is in location to the animal’s body axes and determine how the cells and its desendants will respond to molecular signaling

Two critical regions in a limb bud have profound effects on the limb’s development Apical Ectodermal Ridge – a

thickened area of the ectoderm at the tip of the bud. Removal of it prevent growth of the limb

Zone of Polarizing Activity - a block of mesodermal tissue underneath the ectoderm where the posterior side in attached to the body. It is neccesary for proper pattern formation

Developmental Fate of Cells Hox genes play an

important role in the development of limbs.

Research suggests that pattern formation requires cells to receive and interpret cues from the environment This tells cells where

they are in the developing organ

Mutation in the Hox genes can cause cells in the limb buds to react differently to the positional cues Can cause

polysyndactyly