Lecture AP Biology Chapter 47 Animal development

In this chapter you will: Describe the acrosomal reaction; describe the cortical reaction; distinguish among meroblastic cleavage and holoblastic cleavage; compare the formation of a blastula and gastrulation in a sea urchin, a frog, and a chick; list and explain the functions of the extraembryonic membranes.

Ch 46/47 Warm-Up

1 (Ch 46) How do oogenesis and spermatogenesis differ?

2 (Ch 46) How do these hormones affect the menstrual

cycle?

a) LH

b) FSH

c) Estrogen

d) Progesterone

3 (Ch 47) Describe the process of fertilization.

Chapter 47 Animal Development

What you must know:

• The events that occur when a sperm contacts

an egg

• What occurs in cleavage, gastrulation, and

organogenesis

• Two structures derived from each germ layer

Mammalian Fertilization

1 Sperm binds to receptors in zona pellucida (extracellular

matrix of egg)

2 Acrosomal reaction: sperm releases hydrolytic enzymes to

digest z.p.

(Sea Urchins) Depolarization of membrane: prevent other

sperm from binding = fast block to polyspermy

3 Sperm + Egg Fuse

4 Cortical reaction: sperm + egg fusion triggers release of Ca2+

1 cortical granules fuse with z.p  z.p hardens to form

fertilization envelope = slow block to polyspermy

5 Ca 2+ release also triggers activation of the egg

Fertilization in mammals

Cleavage: rapid mitotic cell division

• Zygote cytoplasm partitioned into smaller cells (blastomeres)

• Solid ball of cells = morula

• Blastula (hollow ball of cells) filled with fluid (blastocoel)

 Blastocyst (human)

Gastrulation: rearrange cells to form 3-layered

embryo w/primitive gut

Ectoderm Mesoderm Endoderm

• Skin, nails, teeth

• Lens of eye

• Nervous system

( brain, spinal cord )

• Skeletal, muscular systems

• Notochord

• Excretory, circulatory

• Reproductive system

• Blood, bone, muscle

• Epithelial linings of

digestive, respiratory, excretory tracts

• Liver, pancreas

* For AP Test, you should know at least 2 derivatives of each germ layer.

Organogenesis: development of 3 germ layers

into organs

• Notochord – stiff dorsal skeletal rod, forms

from mesoderm

• Neural plate  neural tube brain and spinal

cord

• Neurulation – forms hollow dorsal nerve

chord

• Somites – blocks of mesoderm arranged along

notochord; sign of segmentation

Early human embryonic development

Embryo Amniotic cavity with amniotic fluid

Allantois Amnion

Albumen

Yolk (nutrients)

Yolk sac Chorion

Shell

Amniotic embryos (reptiles, birds, mammals)

• Develop in fluid-filled sac w/in a shell or uterus

• Amnion: fluid protects embryo – prevent

dehydration, cushions mechanical shock

• Yolk : nutrients in egg

• Mammalian eggs: little stored food

Patterns of development

• Cytoplasmic determinants: chemical signals such

as mRNAs and transcription factors, influence

pattern of cleavage

• Induction: interaction among cells that influences

their fate, cause changes in gene expression

• Totipotent cells: capable of developing into all

the different cell types

all cells of mammalian embryos are totipotent until the 16-cell stage