Blog which of the following is not a diagnostic feature...

which of the following is not a diagnostic feature of the chordata?

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The chordata phylum is one of fourteen in the animal kingdom and consists of animals that all share a common feature: they all have a nerve cord running down their bodies. This cord is known as a notochord; it becomes the backbone in other vertebrates such as amphibians. Members of the chordate phylum are also known to have gills, an open circulatory system, and an absence of scales on their skin.

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hospital, equipment, medicine @ Pixabay

This article will take you through many different examples from this interesting and diverse group, highlighting some of the key features that make this group so unique.

KEY FEATURES:

Ciliary polarization: the cilia (short hair-like structures) on the surface of cells in an animals primary oocyte (egg cell or ovum) are used to produce a polarizing membrane which helps to align the egg with the sperm. This is also known as “polar body”.

In mammals, eggs have been studied in more detail than any other vertebrate. Research carried out in Singapore and China has helped us understand how the human egg develops. Humans have only one set of chromosomes, which run from one end of the egg all the way through until it hatches.

The first phase of human reproduction starts when the sperm and egg meet. The meeting of sperm and egg is known as fertilization, and occurs in the fallopian tubes. Up to now, most students will have been taught that the sperm flagellum drills a hole through the protective cell layer surrounding the egg which is impregnable to all other cells (the zona pellucida). This allows the sperm to penetrate it and reach an ovum.

In fact, all cells are able to penetrate this protective membrane, which does not have a single hole created by a flagellum in its surface. This membrane is broken by the sperm itself, and penetration results from the action of proteins on the surface of the egg. These proteins are only found on the surface of eggs in their active, or immature, state. Once fertilized, these proteins disappear and are replaced by other ones which prevent further sperm from penetrating.

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laboratory, analysis, diagnostics @ Pixabay

Scientists at Stanford University School of Medicine have found a way to manipulate this process in mice, preventing fertilization but allowing a normal embryo to grow. Their findings could provide a treatment for patients to improve fertility or even space pregnancies.

In humans and many other mammals it is necessary for an egg to be fertilized for pregnancy to proceed. If no male sperm is present the egg will die before it can reach the uterus. If a fertilized egg fails to implant itself in the wall of its uterine cavity, it will be lost.

After an egg is fertilized, it undergoes a series of changes leading to its eventual development into an embryo with all of the cells that will one day give rise to a healthy fetus. If implantation does not occur, however, the developing pregnancy will end very soon after fertilization. Some of these changes are triggered by other cells (known as endometrial), which lined up in groups around the domain where the embryo will grow and develop. This fusion structure is called uterine receptivity or gestational sac (GS).

Within the GS the embryo goes through three distinct stages:

1. Blastocyst: Until this stage, the embryo is a loosely organized structure of stem-cells and cells that will later give rise to the placenta and other structures of the fetus. This stage begins with a small spherical ball of cells which gradually expands in size to form a hollow ball shape, called a blastocyst. The blastocyst is still recognizable at this point as a cluster of cells, but it is now protected by an outer shell formed from other cells that are essential for pregnancy. It has no recognizable features. The inner layer of cells forms the embryo proper, known as morula or zygote. The cells of the inner layer stick together very tightly, forming a small ball which is covered by a flexible outer layer of cells.

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laboratory, analysis, diagnostics @ Pixabay

They will form the tissues and organs of the baby. The outer layer will become the placenta and other extra-embryonic structures that aid in pregnancy. The blastocyst also has an inner cell mass (ICM) which contains stem cells, precursors to all cells in the human body. These stem cells, which can develop into any cell type in the body, are known as pluripotent stem (PS) cells.

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