Animal Development

Question 1

Fertilization steps

Answer 1

1. Acrosome fuses with membrane and releases enzymes that eat through jelly coat of egg
2. Species-specific signals are recognized
3. Contact and fusion of sperm and egg membranes
4. Depolarization of membrane: fast block to polyspermy (non-mammals only)
5. Cortical reaction: cortical granules fuse with plasma membrane and secreted contents clip off sperm-binding receptors and strip vitelline layer away, forming fertilization envelope (slow block to polyspermy)
6. Entry of sperm nucleus

Question 2

Role of Ca+2 in cortical reaction

Answer 2

High concentration of Ca+2 in the egg triggers cortical reaction
Ca+2 spread across the egg correlates with the appearance of the fertilization envelope

Question 3

Activation of egg

Answer 3

Rise in Ca+2 increases rate of cellular respiration and protein synthesis of egg cell
Haploid nuclei fuse and cleavage begins

Question 4

Fertilization in mammals

Answer 4

1. Sperm travel through outer layer of cells to reach zona pellucida (glycoprotein coat; jelly layer)
2. Sperm bind to receptor in zona pellucida
3. Acrosomal reaction
4. Sperm membrane fuses with oocyte
5. Slow block to polyspermy
6. Meiosis II resumes
7. Sperm nucleus is taken into egg
8. Sperm and egg chromosomes are organized onto a single mitotic spindle

Question 5

Blastomeres

Answer 5

Small cells that make up the cytoplasm of one large cell during cleavage

Question 6

Holoblastic cleavage

Answer 6

Complete division of egg

Occurs in species whose eggs have little or moderate amounts of yolk (sea urchins and frogs)

Question 7

Meroblastic cleavage

Answer 7

Incomplete division of egg

Occurs in species with yolk-rich eggs (reptiles and birds)

Question 8

Blastula

Answer 8

Hollow ball of cells

Produced by first several cleavage divisions

Question 9

Blastocoel

Answer 9

Space in blastula

Separates cells: don’t want neighboring cells communicating with each other until proper time

Question 10

Gastrulation

Answer 10

Rearrangement of cells of blastula into 3-layered embryo

Question 11

Gastrula

Answer 11

3-layered embryo formed by gastrulation

Question 12

Germ layers

Answer 12

3 layers produced by gastrulation
Endoderm (lines digestive tract), mesoderm (partially fills space between endoderm and ectoderm), and ectoderm (forms outer layer)

Question 13

Parts of body that ectoderm gives rise to

Answer 13

Epidermis
Nervous and sensory systems
Jaws and teeth

Question 14

Parts of body that mesoderm gives rise to

Answer 14

All other systems that ectoderm and endoderm don’t produce

Skeletal and muscular systems, circulatory and lymphatic systems, excretory and reproductive systems

Question 15

Parts of body that endoderm gives rise to

Answer 15

Digestive tract

Question 16

Organogenesis

Answer 16

Various regions of germ layers develop into rudimentary organs
Mesoderm forms notochord (gives rise to part of spinal cord) and somites (give rise to skeletal muscles and bone among other things)
Ectoderm forms neural plate (turns into neural tube, which gives rise to central nervous system)
Endoderm forms archenteron (gives rise to digestive tract)

Question 17

Induction

Answer 17

One cell population influences development of neighboring cells via interactions at close range

Question 18

Pattern formation

Answer 18

Development of organization of organs and tissues inside embryo’s body

Question 19

Positional information

Answer 19

Molecular cues that control pattern formation

Question 20

Limb buds

Answer 20

Precursors of vertebrate limbs in embryo

Question 21

Apical ectodermal ridge (AER)

Answer 21

Thickened ectoderm at limb bud’s tip

Releases signals that cause limb to extend outward

Question 22

Zone of polarizing activity (ZPA)

Answer 22

Mesodermal tissue where the bottom of the limb bud is attached to the body
Releases signals that differentiate anterior from posterior

Question 23

Sonic hedgehog

Answer 23

Molecule that diffuses out from ZPA providing anterior-posterior positional information to the growing limb