Animal Reproduction and Development
BI 101, Prof. Baack 1
Animal Reproduction
and Development
Reproductive Modes
A) Asexual Reproduction
•Examples: Binary Fission, Budding, Mitosis
B) Sexual Reproduction
•But, Sexual reproduction is more “costly”
1. Specialized structures for gametes
2. Behavioral challenges (courtship)
3. Investment in offspring (nourishment)
Stages of Reproduction/ Development
1) Gamete Formation MEIOSIS
Egg (n) Sperm (n)
Males produce 4 sperm
per germ cell
2n
n n n n
3 polar bodies
2n
n n n n
ovum 4 sperm cells
Gametes start out as (diploid) germ cells)
Females produce 1 egg
per germ cell
2) Fertilization
Zygote (2n)
Fertilization may occur…
b) Internally
•land-dwellers
•specialized structures for housing gametes
•embryo more protected during development
a) Externally
•aquatic habitats
•gametes released into the environment
•large numbers of gametes produced
3) Cleavage:
•A cleavage furrow is formed as the egg dividesinto
numerous smaller cells called blastomeres
•cleavage increases the number of cells but not the
overall volume of the egg
Early cleavage (2 -16 cells) Late cleavage (more than 16 cells)
4) Blastula: “hollow” ball of cells
Blastomeressurround a fluid-filled
cavity called a blastocoel
5) Gastrulation
a) Ectoderm
b) Mesoderm
c) Endoderm
•cellular organization, invagination:
•outermost layer
•
•middle layer
•
•innermost layer
•
•cells become arranged into different germ layers
•Cell differentiation:
