Ch 1: Introduction to Developmental Biology

Comparative Embryology

Study of how anatomy changes during the development of different organisms

evolutionary embryology

The science studying the ways by which developmental changes initiated by the environment can affect evolution. It deals primarily with the evolutionary aspects of developmental symbiosis, developmental plasticity, and niche construction.

teratology

the study of birth defects and of how environmental agents disrupt normal development

epigenesis

The view supported by Aristotle and William Harvey that the organs of the embryo are formed de novo ("from scratch") at each generation

spermism

likeness carried by male semen and semen carried instructions on creation by going through the male body and absorbing mystical vapors

preformation

The view, supported by the early microscopist Marcello Malpighi, that the organs of the embryo are already present, in miniature form, within the egg

chimera

An organism consisting of a mixture of cells from two individuals

gamete

A specialized reproductive cell through which sexually reproducing parents pass chromosomes to their offspring; an egg or a sperm

zygote

A fertilized egg with a diploid chromosomal complement in its zygote nucleus generated by fusion of the haploid male and female pronuclei.

embryo

A developing organism prior to birth or hatching. In humans, the term generally refers to the early stages of development, starting with the fertilized egg until the end of organogenesis (first 8 weeks of gestation). After this, the developing human is called a fetus until its birth

haploid

an organism or cell having only one complete set of chromosomes

diploid

an organism or cell having two sets of chromosomes

blastula

Early-stage embryo consisting of a sphere of cells surrounding an inner fluid-filled cavity, the blastocoel

blastocoel

A fluid-filled cavity of the blastula stage of an embryo

blastopore

The invagination point where gastrulation begins. In deuterostomes, this marks the site of the anus. In protostomes, this marks the site of the mouth.

notochord

A transient mesodermal rod in the most dorsal portion of the embryo that plays an important role in inducing and patterning the nervous system. Characteristic feature of chordates.

neural plate

The region of the dorsal ectoderm that is specified to be neural ectoderm. It later folds upward to become the neural tube.

holoblastic

Refers to a cell division (cleavage) pattern in the embryo in which the entire egg is divided into smaller cells, as it is in echinoderms, amphibians and mammals.

meroblastic

Refers to the cell division (cleavage) pattern in zygotes containing large amounts of yolk, wherein only a portion of the cytoplasm is cleaved. The cleavage furrow does not penetrate the yolky portion of the cytoplasm because the yolk platelets impede membrane formation there. Only part of the egg is destined to become the embryo, while the other portion—the yolk—serves as nutrition for the embryo, as in insects, fish, reptiles, and birds.

isolecithal

Describes eggs with sparse, equally distributed yolk particles, as in sea urchins, mammals, and snails.

telolecithal

Describes the eggs of birds and fish which have only one small area at the animal pole of the egg that is free of yolk.

embryogenesis

The stages of development between fertilization and hatching

birth defect

An abnormality, present at birth, that affects the structure or function of the body

teratogen

Exogenous agents that cause disruptions in development resulting the formation of congenital defects.

malformation

Abnormalities caused by genetic events such as gene mutations, chromosomal aneuploidies, and

translocations

syndrome

Several malformations or pathologies that occur concurrently

disruption

Abnormality or congenital defect caused by exogenous agents (teratogens) such as plants, chemicals, viruses, radiation, or hyperthermia

Theory of Pythagoras

Spermism

Theory of Aristotle

Refuted spermism; believed female menstrual blood served as clay and semen as the sculptor

Theory of Harvey

Refuted spontaneous generation; all organisms arise from eggs

Theory of Paracelsus

Anatomy can only be understood by discovering the nourishment for each part; disease caused by poison brought from the stars; introduced first chemical/mineral medicines

Theory of Wolff

development occurs by epigenesis

Theory of Pander

Defines 3 germ layers

Theory of Van Baer

common pattern in vertebrate animals; notochord directs ectoderm

Theory of Malpighi

looked at development of chicks using microscope images

Vital Dye Staining

Dyes embryonic cells to follow development; as cells split, dye was diluted

Fate mapping

a method of understanding the embryonic origin by illuminating tissue at one stage of development, and their progeny at later stages of development.

CRISPR/Cas9

quickly and inexpensively edits genome; requires guide RNA to specific sequence, viral vector, cas9, and nucleotides

Cre-loxP

complicated and expensive method to knockout genes via cre-recombinase; creates loop with gene and pinches off

GFP fusion constructs

Used to mark cells; inserted into proteins to alter appearance

Microscopy

the use of light or electrons to magnify objects

Six Fundamental Steps of Development

1. Fertilization

2. Cleavage

3. Gastrulation

4. Organogenesis

5. Metamorphosis

6. Gametogenesis

Describe Fertilization

Fusion of two haploid gametes to one diploid zygote

Describe Cleavage

Rapid Division; S and M phase occur, which G is skipped; New cells called blastomeres

Describe gastrulation

Rearrangement of cells of the blastula to form three germ layers

Describe organogenesis

Regions of the embryonic germ laters form rudiments of organs; localized changes in tissue and cell shape

Describe metamorphosis

birthed organism matures to become a sexually mature adult

Describe gametogenesis

production of gametes (meiosis)

What develops in the embryonic stage?

CNS, heart, arms, eyes, legs, teeth, palate, external genitalia, ears (H.A.L. only develops in embryo)

What develops in the fetal stage?

CNS, eyes, teeth, palate, external genitalia, ears

Describe the cleavage type, yolk distribution, and embryo nourishment in mammals.

Holoblastic Cleavage

Isolithical

Placenta

Describe the cleavage type, yolk distribution, and embryo nourishment in sea urchin.

Holoblastic Cleavage

Isolithical

Larva

Describe the cleavage type, yolk distribution, and embryo nourishment in birds.

Meroplastic

Terolithical

Yolk

What determines cleavage patterns?

the amount and distribution of the yolk

What are the three germ layers?

ectoderm, mesoderm, endoderm

Give an example of organs/tissues in the ectoderm.

Epidermis, Melanocytes, CNS, Neural Tube, Neural Crest, Mammary Glands, Inner Ear, Retina, Hair/Nails, Posterior Pituitary, Pineal Glands

Give an example of organs/tissues in the mesoderm.

Bone, Muscle, Connective Tissue, Blood, Heart, Blood Vessels, Kidney, Bladder, Spleen, Dermis, Gonads, Adipose

Give an example of organs/tissues in the endoderm.

Epithelium of GI, Thyroid, Pharynx, Lung/Respiratory Track, Pancreas, Liver

What are the three axes determined via gastrulation?

Transverse Plane (Determines Anterior/Posterior)

Frontal Plane (Determines Dorsal/Ventral)

Give an example of the transverse plane in a species.

This planes divides a human's cranial and caudal ends.

Give an example of the midsaggital plane in a species.

This plane divides a human's right and left sides

Give an example of the frontal plane in a species.

This plane divides a human's ventral and dorsal sides

What is the output of mitosis?

Two diploid daughter cells

What is the output of meiosis?

4 haploid daughter cells.

Recommend an experiment to test the influence of a gene on the proper development of an organism and hypothesize the possible outcome(s) of your experiment.

Find It, Move It, Lose It; Locate a gene that is suspected to develop mammary glands, move this gene to a different location, and remove the gene altogether, and allow a control. Moving/Removing the gene will interrupt development of the glands.

Provide one example with rationale of a disruption and one example of a malformation.

Disruption: Thalidomide taken by pregnant women resulted in limb developmental issues

Malformation: Cleft Lip caused by genetic variant

What is a model organism?

a species that is easy to grow in the lab and lends itself particularly well to the questions being investigated

Why do we use model organisms?

-Smaller size makes them more suitable for labs

-Less expensive

-More ethical

What are the best/worst model organisms?

Best: Mice, Flies, Chicks, Plants

Worst: Humans, Large Mammals