Development 1: Mammalian Fertilization and Cleavage Patterns Study Guide

What is the definition of development in biology?

All changes that occur during the entire life cycle, including embryonic and post-birth/hatching stages.

What are model organisms?

Species chosen for research that are easily studied.

What is the outcome of fertilization?

Restores diploid (2n) state, often determines sex, and activates the egg to promote development.

What are the major steps in fertilization?

Sperm dissolves protective layers, binds to surface receptors, changes egg surface to prevent polyspermy, and nuclei fuse.

What is polyspermy?

The fertilization of an egg by multiple sperm, which can lead to abnormal chromosome numbers.

What is the acrosomal reaction?

The process where the sperm pushes through follicle cells, binds to receptors in the zona pellucida, and releases enzymes to aid in fertilization.

What are the three effects of the calcium wave released during fertilization?

1. Triggers cortical reaction; 2. Activates the egg; 3. Completes meiosis and fuses nuclei.

What is the cortical reaction?

The fusion of cortical granules with the plasma membrane, releasing enzymes that harden the zona pellucida and block polyspermy.

What is the significance of the secondary oocyte being arrested at metaphase II?

It requires a calcium trigger to complete meiosis upon fertilization.

What is karyogamy?

The fusion of the sperm nucleus with the egg nucleus, resulting in a diploid zygote.

What marks the end of fertilization?

When the zygote undergoes its first division, typically 12-26 hours after fertilization in mammals.

What is cleavage in embryonic development?

The process where the zygote undergoes rapid cell divisions without growth, forming a multicellular embryo.

How does yolk affect cleavage patterns?

The amount and distribution of yolk influence the speed and symmetry of cell divisions.

What is holoblastic cleavage?

Complete division of the zygote into equal-sized cells, seen in organisms with little yolk.

What is unequal holoblastic cleavage?

Asymmetric cleavage due to yolk distribution, resulting in unequal cell sizes, common in amphibians.

What is meroblastic cleavage?

Only regions without yolk divide completely, seen in reptiles, birds, and many fish.

What is a blastula?

A hollow embryo formed during the cleavage stage, characterized by the presence of a blastocoel.

What is the role of the zona pellucida?

A glycoprotein matrix that surrounds the egg, playing a crucial role in fertilization and preventing polyspermy.

What triggers the onset of embryonic development?

A series of metabolic reactions initiated by calcium ions in the cytoplasm of the egg.

What is the diploid zygote's potential?

It is totipotent, meaning it has the potential to give rise to all cell types.