Embryology Questions Essay Samples

- The stromal cells that are found in the developing gonads of tetrapods begin from the medulla from the peritoneal wall and the cortex from inter-renal blastema or mesonephric. Hence the gonads have a dual origin.
- Spermatogenesis occurs in a syncytial complex because it involves the formation of sperm from undifferentiated cells that are first attached to rachis. Syncytial cell complex or syncytium result when cells with single nuclei fuse to for a cell with nucleus. Syncytial cell complex is vital in oogenesis in that it assists in the differentiation of cells. One other developmental model is vitellogenesis.
- Spermatogenesis occurs in a syncytial complex because it involves the formation of sperm from undifferentiated cells that are first attached to rachis. Syncytial cell complex or syncytium result when cells with single nuclei fuse to form a cell with a nucleus. Syncytial cell complex is vital in oogenesis in that it assists in the differentiation of cells. One other developmental model is vitellogenesis. The polar bodies are formed during oogenesis because they are non-functional. In the end, only one mature ovum is formed once in every month. However, in spermatogenesis, the sex cell divides to form four haploid cells that become sperm hence polar bodies are not formed since they are non-functional and cannot develop to become sperms.
- In Na+-depleted sea water, the polyspermic fertilization of the sea urchin will be increased. This is because depletion of Na+- in sea water enhances sperm viability. In Na+-depleted sea water, cell motility is decreased, ATP concentrations are elevated and acrosome reactions are prevented.
- Addition of EGTA to the extracellular medium will enhance cortical reactions hence inhibit polyspermy.
- An experiment where a female mouse with an inactivated ZP3 gene has been found to produce eggs that lack the zona and are infertile. It is indicated that ZP3 is in charge for the species-specific binding capability of sperm to the zona through numerous proteins that are on the sperm surface that bind to particular O-linked oligosaccharides on ZP3. ZP3 is the trigger for the acrosome reaction in the zona that significantly induces the influx of Ca2+ that are also necessary for the acrosome reactions in mice.
- Mice, Zebrafish, the frog are commonly used as vertebrate model systems. The advantages for using zebrafish are that they have good genetics that are nearly saturated for zygotic patterning mutants. Also, the organ systems are similar to other vertebrates. The limitations include: they cannot make transgenic animals with ease, and they are not trivial to clone genes. The frog has advantages of exceptional experimental embryology embedding induction preparations and expression of ectopic gene is possible in early embryos. The limitations are: no genetics and no targeted gene disruption can occur. Thirdly, the mouse has brains that are similar to humans hence easy to compare, and the developmental overview is similar to that of all other mammals. The limitations: it’s difficult to study early-acting mutant phenotypes, and embryonic manipulations are also difficult inside the organism.
- A stem cell is an undifferentiated cell found in a multicellular organism which can reproduce more cells of the same type. It is from the stem cell that certain other kinds of cells emerge by differentiation. Stem cells are utilized during spermatogenesis through undergoing meiosis and mitosis processes that give rise to numerous similar cells. Hence, they increase the chances of survival and fertilization during the ejaculation process. They are located in the basement membrane of the seminiferous tubules.
- Cortical reaction is described as a process taking place during fertilization by the release of cortical granules from the egg that inhibits multiple fusions of sperms with an egg or polyspermy. In an experiment conducted on mice, it is indicated that ZP3 induces the influx of Ca2+ and this triggers the cortical reaction.
- A) Actin filaments which are 7-8 nm in diameter B) Monomeric subunits namely; microfilaments and thin filaments. C) Actin monomers are oriented in the same direction, and they have distinct polarity and their ends are distinguishable from each other due to their plus and minus ends. D) Globular (G) actin and filamentous (F) actin are the associated motor complexes. E).
A) Intermediate filaments that measure 10 nm in diameter B) they are made of cytoplasmic fibers such as keratins, neurofilaments and nuclear lamina C) they provide a supporting framework. The last type is the microtubules that measure 25 nm in diameter and structurally look like straight, hollow cylinders. The associated proteins include α-tubulin and β-tubulin dimers.
- The motor complexes of 2 cytoskeletal systems are able to transduce the chemical energy in the process of ATP hydrolysis into motions and forces in cells. Thus, they are referred to as mechanochemical ATP motors.
- Spermatogenesis and Oogenesis have similarities and differences. Some similarities are both of them pass through the processes of meiosis I and II. Moreover, at the beginning of both processes the cells are diploid. In the end, there are four haploid cells. The differences are spermatogenesis is a process that involves the formation of gametes while oogenesis is the formation of egg cells. Spermatogenesis takes place in the sperm cell while oogenesis takes place in female ovaries. In spermatogenesis, all the daughter cells become a sperm while, in oogenesis, only one daughter cell becomes ovum. The other three become polar bodies. Spermatogenesis starts at puberty and end after a person dies. It takes seven weeks to complete and the process involves the formation of millions of sperm. Oogenesis, on the other hand, starts before birth and ends at menopause. It takes 13-50 years to finish and it only involves the formation of one ovum.
- A cyclin is a protein that signals cells to move to another process during cell division. Cyclin is given this name because they go through a constant process of synthesis degradation and cell division. A synthesized cyclin acts as an activator for protein synthesis.
- Cyclin-Dependent protein Kinase is an enzyme that helps to add phosphate groups to molecules. The phosphate groups added are negatively charged, and Cyclin-Dependent protein Kinase does this through a process called phosphorylation. After cyclins have undergone synthesis, they attach to Cyclin-Dependent protein Kinase forming a complex. The attachment to the enzymes signals the cells to move to the next process. When the protein degrades and detaches from the enzyme it signals the end of the process.
- Immediately after fertilization, somatic cells undergo two processes namely interphase and M phase. Interphase is divided into three groups namely GI, S and G2. M phase involves cell division and it includes mitosis and cytokinesis. Gap 1 involves growth and formation of protein. After this phase is S phase that involves the synthesis of DNA. G2 involves biochemical processes. On the other hand, eumetazoan maternally-driven animal cells involve a process called mitosis. It involves prophase, prometaphase, metaphase, anaphase and telophase. This division, unlike that of somatic cells, does not involve interphase. However, it has the three stages namely G1, S and G2. The molecules in extracellular matrix and proteins account for a significant difference in the rates of cell division.
- Mitosis and Meiosis are ways in which cells can undergo division and reproduction. Mitosis is usually described as a method in which cell duplicates. In this process, a single cell leads to two identical ones. Meiosis, on the other hand, is defined as a division of germ cells. The process entails fission of nucleus leading to haploid cells. Each cell has half the parent chromosomes. The function of meiosis is sexual reproduction while mitosis is cellular reproduction and growth of the body. Meiosis happens in sexual reproduction while mitosis is asexual reproduction. Meiosis involves pairing of Homologs while mitosis does not. The number of divisions in Meiosis is 2 while that of Mitosis is 1. In Meiosis there is crossing of chromosomes while, in mitosis, the process does not occur. Meiosis has two divisions namely Meiosis I and I. Meiosis is defined as a division of germ cells. Meiosis II is the second part of Meiosis which is similar to mitosis in that it involves the processes of interphase, prophase, Metaphase, Anaphase, Telophase and cytokinesis. In Meiosis I the chromatids stay side by side at Metaphase. The chromatids start separating at anaphase and completely separate at telophase. In meiosis II homologous pairs separate into four cells. In Meiosis I there is replication of DNA while, in Meiosis II, there is no replication of DNA.
- Differentiation is defined as the process where cells specialize. Morphogenesis, on the other hand, is when a cell develops to become what it is supposed to be. Differentiation is usually triggered by signals while morphogenesis is not. Morphogenesis is an all-inclusive process while differentiation is specific. Differentiation is a function of morphogenesis because it allows morphogenesis to take place.
- An embryo is multicellular diploid eukaryote which is in its early stage of development before it is born. In placental mammals, an embryo is the organism between first cell division of a zygote up to the time when it becomes a fetus. Embryogenesis is the process of development that begins once an egg is fertilized until it becomes a fetus. The process begins with the fertilization of an ovum by a sperm. This fertilized ovum is now referred to as a zygote. Then it undergoes mitosis divisions but with unnoticeable growth change, a process known as cleavage, and then the differentiation of cells leading to embryo development. Developmental biology is the process of development of organs and their growth. Developmental biology also involves the study of genetic control of cell differentiation, cell growth and also morphogenesis. Parazoan is not microscopic and have differentiated body cells, but they don’t have tissues or organs. An example is sponges. Metazoans are multicellular animals that form the major portion of the animal kingdom. They have specialized tissues or organ systems.
- Extracellular matrix plays a vital role in morphogenesis. It influences the germ cells by keeping the tissues apart, providing a structure for support and cells to move from one process to the other. Extracellular matrix has three molecules namely collagen, laminin and fibronectin. The molecule that seems important primordial germ cells is fibronectin for it assists the cells to reach final destination.
- Chemical method of determining the importance of glycosylated residues involves staining. Biochemical procedures involve saccharide binding proteins, enzymes and antibody.
- Chemotaxis is a process in which chemicals trigger movements in somatic cells or bacteria. The organisms move according to chemicals in their environments. Chemotaxis contributes to specie-specific fertilization. Sperm protein binding is the one accorded the responsibility of determining the binding sperm to an egg in species-specific clinging. The movement of the sperm to an egg is directed by chemotaxis.
- The accessory cells are; pleomorphic accessory cells (AC-I) and amoeboid accessory cells (AC-II) The accessory cells are used in the supply of nutrients for germ cell development during spermatogenesis. Accessory cells are also believed to play some role in resorption of degenerating sperms after discharging of sperms for germ cell development.
- One of the contraceptives will be one made from cortical granules cells. This will form an inhibition around ovum preventing fertilization. The second one will be anti- acrosome development contraceptive. This will inhibit the formation of acrosome at sperm maturation hence inhibit fertilization. The third one is contraceptive for inhibition of chemotaxis by altering the chemical balance in the reproduction system hence there will be no travelling of sperm to the ovum rather it moves away from the ovum.
- Fast block polyspermy is where there is temporary blocking of additional sperms from fertilizing an egg. While in the slow block polyspermy, the cortical reaction gradually establishes a permanent barrier that prevents extra sperm from fertilizing an egg.
- (a)
(i) Both cortical granules and acrosomes contain enzymes.
(ii) They both have extracellular protein matrix deposited on the surface.
(iii) Both are involved in the reproduction process in mammals.
(b) (i) The cortical granules for a barrier that prevents sperm entry into than egg while acrosomes have enzymes that break down outer membrane of an ovum allowing the sperm to fuse with the ovum.
(ii) The cortical granules are formed on the surface of the ovum or egg while acrosomes are formed on the anterior half of the head of sperm surface.