Comparative Embryology and Animal Development Flashcards

Flashcards based on lecture notes about comparative embryology and animal development, covering topics from fertilization to gastrulation and the roles of different egg types.

What is comparative embryology?

The study of the similarities and differences in the embryos of different species, providing insights into developmental processes and evolutionary relationships.

How does comparative embryology relate to evolution?

It demonstrates common ancestry by showing similar developmental stages in different species and helps understand evolutionary relationships and adaptations.

What are homologous structures?

Anatomical features that are similar due to shared ancestry, even if their functions differ, such as forelimbs of mammals or early embryonic features like tails and pharyngeal arches in vertebrates.

What are some embryonic similarities among vertebrates?

Presence of a notochord, pharyngeal arches, and tail structures during early development, indicating a common evolutionary pathway.

What do pharyngeal arches develop into in fish and mammals?

In fish, they become gills; in mammals, they develop into parts of the ear and throat, illustrating how homologous structures can adapt to different functions.

What is the significance of studying homologous structures like tails and pharyngeal arches in the context of evolution?

It supports the theory of evolution by common descent and aids in tracing evolutionary pathways and adaptations among vertebrate species.

What characterizes deuterostomes and what animal groups belong to Deuterostomes?

A major lineage of animals that include vertebrates and echinoderms characterized by their embryonic development, where the blastopore becomes the anus.

What is fertilization?

The process by which a sperm cell and an egg cell combine to form a zygote, marking the beginning of a new organism's development.

Describe the structure of a sperm cell.

A motile cell with a head containing the nucleus and acrosome, a midpiece packed with mitochondria, and a flagellum for movement.

Describe the structure of an egg cell.

A larger, non-motile cell containing cytoplasm, nucleus, and protective layers such as the zona pellucida in mammals.

How does sperm penetrate the egg during fertilization?

The acrosome reaction releases enzymes that help the sperm penetrate the egg, and the sperm and egg plasma membranes fuse, allowing the sperm nucleus to enter the egg.

What mechanisms prevent polyspermy?

Fast block: A rapid change in membrane potential upon sperm entry. Slow block: The cortical reaction leads to the formation of a fertilization membrane.

What happens after sperm entry to form the zygote?

The egg completes meiosis if it hadn't already, male and female pronuclei fuse to form a diploid zygote nucleus, and the zygote begins its first mitotic division.

What is cleavage?

A series of rapid mitotic divisions without growth, leading to the formation of a blastula; cleavage patterns may vary depending on the amount of yolk in the egg.

What are the three main types of eggs based on yolk content?

Isolecithal, mesolecithal, and telolecithal.

Describe isolecithal eggs.

Eggs with a small amount of evenly distributed yolk, found in invertebrates like sea stars and some mammals, resulting in holoblastic cleavage.

Describe mesolecithal eggs.

Eggs that contain a moderate amount of yolk concentrated in one hemisphere, common in amphibians like frogs, where cleavage is holoblastic but slowed in the yolk-rich vegetal pole.

Describe telolecithal eggs.

Eggs with a large amount of yolk concentrated at one end, found in birds, reptiles, and some fish, resulting in meroblastic cleavage.

What is the difference between holoblastic and meroblastic cleavage?

Holoblastic cleavage involves complete division of the egg, occurring in isolecithal and mesolecithal eggs, while meroblastic cleavage is partial due to the large yolk in telolecithal eggs.

What is gastrulation?

A critical phase in embryonic development where the single-layered blastula reorganizes into a multi-layered structure called the gastrula, establishing the three primary germ layers.

What cell movements occur during gastrulation?

Cell movements include invagination (inward folding), involution (rolling inwards), and migration, transforming the blastula to create the archenteron (future gut) and the blastopore (opening).

What are the three primary germ layers and what do they develop into?

Ectoderm (outermost layer): Develops into the skin, hair, nails, and nervous system. Mesoderm (middle layer): Forms muscles, bones, blood, and internal organs. Endoderm (innermost layer): Develops into the digestive tract and associated organs.