BIOL 3542 - Lecture 1

Development (definition)

Refers to how multicellular organisms arise through a relatively slow process of progressive change

Development begins with…

It beings with a single cell, otherwise known as the fertilized egg/zygote

Development (process)

It begins with the zygote and then produces, differentiates and organizes millions of cells that becomes an individual that is ready to be born and eventually reproduce

Development (3 parts)

1.) Production

2.) Differentiation

3.) Organization

Production (in development)

One cell gives rise to millions of cells

Differentiation (in development)

Different cells specialize into specific functions

Organization (in development)

When cells organize themselves to ensure that the individual is functional

What is the organism called in the time between fertilization and birth

An embryo

Embryology

The study of animal development between fertilization and birth (mostly descriptive)

Does development stop after birth?

No, growth continues until maturity and can sometimes involve regeneration and metamorphosis (depending on the species)

Is regeneration and metamorphosis still involved in development?

Yes

Developmental biology (definition)

The study of cellular and molecular mechanisms that drive changes in cells, tissues and organs over time, specifically focusing on the mechanistic understanding of development

Developmental biology includes…

Embryology and adult forms of development (i.e. regeneration and metamorphosis)

Life cycle of frogs

1.) Fertilization

2.) Cleavage

3.) Gastrulation

4.) Organogenesis

5.) Three body axes

6.) Metamorphosis

7.) Gametogenesis

Fertilization

Refers to the fusion of the mature sex cells, including its nuclei, which gives the embryo its genome

Fertilization of the frog

It occurs externally and is controlled by environmental factors

How is the fertilization of frogs controlled by environmental factors

1.) Only occurs seasonally

2.) It only lays its eggs in pond vegetation

Fertilization activates…

It activates molecules necessary to initiate the next 2 steps in the life cycle (cleavage and gastrulation)

Dark vs. light parts

Dark parts = where the nucleus is

Light parts = where the cytoplasmic contents are

Cleavage

A series of mitotic divisions that divides the cells into blastomeres, but the volume of the zygote stays the same (just has more compartments)

Name of the embryo at the end of cleavage

Blastula

Gastrulation

A series of extensive cell rearrangements where mitotic division slows down, but the blastomeres undergo dramatic movements, as the cells start to organize themselves

Gastrulation begins at the…

Blastopore

Blastopore

It is an opening of the central cavity during development that is 180º opposite of the sperm entry

As a result of gastrulation, the embryo contains…

Three germ layers, the ectoderm, the mesoderm, and the endoderm

Organogenesis

1.) Cells in different germ layers exchange chemical signals as a way of communicating

2.) Cell interactions and rearrangements then result in the production of specific organism at specific sites

AP axis

The “anterior-posterior” axis (Anterior = head, Posterior = tail)

DV axis

The “dorsal-ventral” axis (Dorsal = back, Ventral = belly)

RL axis

The “right-left:” axis, which separates the sides of the body

Are humans symmetrical?

On the outside they are, but their organs and the contents of their cells are not

Metamorphosis

Only occurs in certain species, where the individual undergoes dramatic changes, to the point where almost every organ is subject to modification

Metamorphosis of frogs

They go from aquatic tadpoles to adult frogs that live on land

Gametogenesis

Once metamorphosis ends, the development of the germ cells begin, allowing for meiosis to occur

Meiosis

Cell division where the number of chromosomes half, producing haploid gametes as a result