Cell Biology 222: Developmental Biology

Study Notes

Developmental biology studies the processes that transform a zygote to a complex organism.
Asexual reproduction produces genetically identical offspring from a single parent.
Sexual reproduction combines genetic material from two parents, creating genetically diverse offspring.

Sexual reproduction involves the fusion of gametes (egg and sperm) from two parents.
This mixing of genetic material leads to offspring that are genetically unique.
Offspring inherit traits from both parents, providing genetic variation crucial for adaptation and survival.
Sexual reproduction allows for the combination of beneficial traits and the elimination of harmful ones from the gene pool over generations.

Germ cells (gametes) are haploid, containing a single set of chromosomes.
Somatic cells are diploid, containing pairs of chromosomes.
Meiosis creates haploid germ cells from diploid cells.
During meiosis, chromosomes separate and recombine, leading to genetically unique gametes.
Fertilization of egg and sperm restores the diploid state in the zygote.

Cleavage refers to the early cell divisions after fertilization.
The zygote undergoes rapid cell divisions without significant growth, resulting in increasingly smaller cells.
Blastomeres are the cells produced during cleavage.
This process creates a solid ball of cells called a morula.
Blastomeres rearrange into a hollow ball of cells called a blastula.

Gastrulation is the process by which the blastula reorganizes into a gastrula.
Three germ layers are formed during gastrulation:
- Ectoderm: The outer layer – gives rise to skin, nervous system, and other tissues.
- Endoderm: The inner layer – gives rise to lining of the digestive tract, lungs, and other internal organs.
- Mesoderm: Lies between ectoderm and endoderm – gives rise to muscles, blood, circulatory system, and other tissues.
These layers differentiate into various tissues and organs during organogenesis.

The presentation shows various stages of human embryo development observed in a laboratory setting.
The images illustrate the sequential changes occurring in early embryo growth.

Ectoderm: Develops into the epidermis, hair, nails, claws, sweat glands, tooth enamel, central nervous system (CNS).
Mesoderm: Develops into muscles, blood, blood vessels, heart, spleen, reproductive organs, and kidneys.
Endoderm: Develops into the linings of the digestive and respiratory systems, liver, gallbladder, and pancreas.