ZOO501T Midterm Past Papers 2023 by Sulman Ali

ZOO501- DEVELOPMENTAL BIOLOGY · Mid-Term File 2023 By · SULMAN ALI (BS-ZOOLOGY)

Structure of Sperm?

The sperm has a head and tail. The head is oval-shaped and is only 10% of the overall length of the sperm. It contains the male genetic material in a structure called the nucleus. In addition to DNA, the sperm head also contains astructure called the acrosome.

Development biology:

Development biology is a discipline that studies embryonic and other developmental processes. It is the study of the process by which animals and plants grow and develop. Developmental biology also encompasses the biology of regeneration, asexual reproduction, metamorphosis, and the growth and differentiation of stem cells in the adult organism.

Cleavage is found in sea urchins:

Sea urchins exhibit radial holoblastic cleavage. The first and second cleavages are both meridional and are perpendicular to each other. That is to say, the cleavage furrows pass through the animal and vegetal poles. The third cleavage is equatorial, perpendicular to the first two cleavage planes, and separates the animal and vegetal hemispheres from one another. The fourth cleavage, however, is very different from the first three. The four cells of the animal tier divide meridionally into eight blastomeres, each with the same volume. These cells are called mesomeres. The vegetal tier, however, undergoes an unequal equatorial cleavage to produce four large cells, the macromeres, and four smaller micromeres at the vegetal pole.

What is different B/W Sex and Fertilization?

Fertilization: Fertilization is the process whereby two sex cells (gametes) fuse together to create a new individual with genetic potentials derived from both parents. Sex involves the combining of genes from two different individuals into new arrangements.

Events of fertilization:

Fertilization consists of four major events:

1= Contact and recognition between sperm and egg. In most cases, this ensures that the sperm and egg are of the same species. 2= Regulation of sperm entry into the egg. Only one sperm can ultimately fertilize the egg. 3= Fusion of the genetic material of sperm and egg. 4= Activation of egg metabolism to start development.

Differenence between Animals pole and vegetal pole?

The region of the ovum which extrudes polar bodies and receives sperm is called animal pole, whereas the pole of the ovum opposite to the animal pole is known as vegetal pole.

Role of MPF:

MPF was first discovered as the major factor responsible for the resumption of meiotic cell divisions in the ovulated frog egg. It continues to play a role after fertilization, regulating the biphasic cell cycle of early blastomeres. Cleaving cells can be experimentally trapped in S phase by incubating them in an inhibitor of protein synthesis. When MPF is microinjected into these cells, they enter M. Their nuclear envelope breaks down and their chromatin condenses into chromosomes. After an hour, MPF is degraded and the chromosomes return to S phase. The primary function of MPF is

1= to promote spindle assembly, 2= chromatin condensation and 3= the breakdown of the nuclear envelope.

Vegetal Hemisphere:

The bottom half of the egg usually contains the yolk, it divides more slowly (because the large yolk deposits interfere with cleavage). This portion is the vegetal hemisphere of the egg. It is the region that is the lower, light-colored hemisphere of the egg, as its cells contain large amounts of dense yolk proteins.

What is microvilli:

Microfilaments are necessary for cell division, and they also are used to extend the egg surface into small projections that is called microvilli, which may aid sperm entry into the cell.

Diff between germ and somatic cell examples:

Germ Cell: In many species a specialized portion of egg cytoplasm gives rise to cells that are the Precursors of the gametes (the sperm and egg). The gametes and their precursor cells Are collectively called germ cells, and they are set aside for reproductive function. Example: Germ cells are egg cells in females and sperm cells in males.

somatic cell: All the other cells of the body are called Somatic cells. This separation of somatic cells (which give rise to the individual body) and germ cells (which contribute to the Formation of a new generation) is often one of the first differentiations to occur during Animal development. Examples: are muscle cells, blood cells, skin cells and nerve cells.

4 levels of Regulation of gene expression?

The regulation of gene expression can be accomplished at several levels:

•  Differential gene transcription: It regulates that which of the nuclear genes is transcribed into RNA.
•  Selective nuclear RNA processing: It regulating which of the transcribed RNAs (or which parts of such a nuclear RNA) enterinto the cytoplasm to become messenger RNAs.
•  Selective messenger RNA translation: It regulates that which of the mRNAs in the cytoplasm becomes translated intoproteins.
•  Differential protein modification: It regulates that which proteins are allowed to remain or function in the cell.

The two components of acrosomal reaction in sea urchins?

In most marine invertebrates, the acrosomal reaction has two components:

•  The fusion Of the acrosomal vesicle with the sperm plasma membrane (an exocytosis that results In the release of the contents of the acrosomal vesicle).The extension of the acrosomal Process. The acrosomal reaction in sea urchins is initiated by contact of the sperm with The egg jelly.
•  The second part of the acrosomal reaction involves the extension of the Acrosomal process. This protrusion arises through the polymerization of globular actin Molecules into actin filaments. The egg jelly factors that initiate the acrosomal reaction In sea urchins are often highly specific to each species.

What is naive?

An uncommitted cell can be described as naive, meaning that it has received no instructions directing it along a particular developmental pathway.

What is egg jelly?

Many types of eggs have glycoprotein meshwork called egg Jelly outside the vitelline envelope which is used either to attract or to activate sperm. The Egg, then, is a cell specialized for receiving sperm and initiating development.

The basic anatomy of eukaryotic gene:

The structure of eukaryotic genes. Most eukaryotic genes contain segments of coding sequences (exons) interrupted by noncoding sequences (introns). Both exons and introns are transcribed to yield a long primary RNA transcript.

Role of calcium in cortical reaction?

Role of calcium in cortical reaction Upon fertilization, the intracellular calcium ion concentration of the egg increases greatly. In this high-calcium environment, the cortical granule membranes fuse with the egg plasma membrane, releasing their contents. Once the fusion of the cortical granules begins near the point of sperm entry, a wave of cortical granule exocytosis propagates around the cortex to the opposite side of the egg. Several experiments have demonstrated that calcium ions are directly responsible for propagating the cortical granule reaction, and that these calcium ions are stored within the egg itself.

Classes of cadherin:

1= E-cadherin: a. Epithelial cadherin is expressed on all early mammalian embryonic cells, even at the 1cell stage. Later, this molecule is restricted to epithelial tissues of embryos and adults.

2= P-cadherin: a. Placental cadherin appears to be expressed primarily on the trophoblast cells (those placental cells of the mammalian embryo that contact the uterine wall) and on the uterine wall epithelium.

3= N-cadherin: a. Neural cadherin is first seen on mesodermal cells in the gastrulating embryo as they lose their E-cadherin expression. It is also highly expressed on the cells of the developing central nervous system.

4= Protocadherins: a. Calcium-dependent adhesion proteins that differ from the classic Cadherins in that they lack connections to the cytoskeleton through catenins. Protocadherins have been found to be very important in separating the notochord from the other mesodermal tissues during Xenopus gastrulation.

How cleavage cell can be trapped?

Cleaving cells can be experimentally trapped in S phase by incubating them in an inhibitor of protein synthesis. When MPF is microinjected into these cells, they enter M. Their nuclear