Animal Reproduction and Development

Reproductive Modes

A) Asexual Reproduction

• Examples: Binary Fission, Budding, Mitosis

one organism creates a genetically similar copy of itself without the combination of genetic material with another individual

Reproductive Modes

B) Sexual Reproduction

• Sexual reproduction is more “costly”, requiring 1. Specialized structures for gametes 2. Behavioral challenges (courtship) 3. Investment in offspring (nourishment)

Organisms with two different adult sexes create descendants through the combination of genetic material. Creates new genetic combinations.

Figure 8.13

Haploid gametes (n = 23)

Diploidzygote

(2n = 46)

Multicellulardiploid adults

(2n = 46)

Mitosis anddevelopment

Egg cell

Sperm cell

Meiosis Fertilization

Stages of Reproduction/ Development

1) Gamete Formation MEIOSIS

Egg (n) Sperm (n)

Males produce 4 sperm per germ cell

2n

n n n n3 polar bodies

2n

n n n novum 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:

• Cleavage is a special type of cell division that creates the multicellular embryo from a single-celled zygote.

• During cleavage the cytoplasm pinches in, forming a cleavage furrow

• The embryo does not actually grow in size.  Instead, the zygote is divided into many smaller cells called blastomeres.

The result of dividing the zygote in this way is that different blastomeres will contain different cytoplasmic components.

...morula - a solid ball of cells produced by continued cleavage

• blastula - hollow ball of cells formed when a fluid-filled cavity called the blastocoel forms within the morula

• Gastrulation refers to the invagination or infolding of the blastula.

• Once the infolding has begun, we refer to the embryo as a gastrula

4) Gastrulation

Blastula Early Gastrula Late Gastrula

a) Ectoderm

b) Mesoderm

c) Endoderm

• outermost layer• nervous system, outer layer of skin

• middle layer• muscle, skeleton, circulatory, reproductive, excretory, connective tissues

• innermost layer• inner lining of gut and associated organs

Gastrulation rearranges the cells into different germ layers

• Cell differentiation: the process by which an unspecialized cell becomes specialized (examples: heart, liver, or muscle cells)

• certain genes are activated (turned on)• other genes are inactivated (switched off)

The shape and structure of tissues, organs and the entire organism are formed. • Cells continue to divide and migrate• programmed cell death sculpts body parts

5) Organogenesis:

6) Morphogenesis:

Organ formation. Each of the embryonic germ layers gives rise to the framework for some organ systems.

Embryos may develop in several ways

A) Oviparous

B) Ovoviviparous

C) Viviparous

• young develop and hatch from eggs laid outside of the mother’s body

• nourished by the yolk of the egg• all birds and many fish, amphibians and reptiles

• young develop and hatch from eggs within the uterus, and the mother gives birth to live young

• nourished by the yolk of the egg• certain fishes, sharks, and reptiles and

many invertebrates

• young develop directly inside the mother and she gives birth to live young

• nourished by mother’s tissues (placenta)• mammals

Study Objectives

1. Define asexual reproduction and give 3 examples.2. Define sexual reproduction. What are some costs of reproducing sexually? 3. List the 6 stages of reproduction/development. 4. Contrast external and internal fertilization. In general, which type of organisms carry out each of these processes?5. Define meiosis and fertilization. Contrast sperm and egg production.6. Define cleavage. How does cleavage occur and what does it accomplish? Explain the role of cleavage in cell differentiation.7. Define blastomere, blastula, and blastocoel.8. Explain what happens during gastrulation. 9. What are the three germ layers? To what do these give rise in the mature organism?10. Define invagination. Define differentiation.11. Define organogenesis.12. Explain what happens during metamorphosis. 13. Compare and contrast oviparous, ovoviviparous, and viviparous development.