ZOO501 Final Term Solved Papers by Zareen Warraich

ZOO501-Developmental-Biology · ZAREEN WARRAICH. FUTURE ZOOLOGIST GROUP · Solved Questions FINAL TERM (current PAPERS) February2020

Q1. Polyspermy (2 marks)

The entrance of multiple sperm polyspermy leads to disastrous consequences in most organisms. In the sea urchin, fertilization by two sperm results in a triploid nucleus, in which each chromosome is represented three times rather than twice (Worse condition). Species have evolved ways to prevent the union of more than two haploid nuclei. The most common way is to prevent the entry of more than one sperm into the egg.

polyspermy describes an egg that has been fertilized by more than one sperm. Diploid organisms normally contain two copies of each chromosome, one from each parent. The cell resulting from polyspermy, on the other hand, contains three or more copies of each chromosome—one from the egg and one each from multiple sperm. Usually, the result is an inviable zygote

Q2. Zona pellucida (2 marks)

Zona pellucida: The strong membrane that forms around an ovum as it develops in the ovary. The membrane remains in place during the egg's travel through the fallopian tube. To fertilize the egg, a sperm must penetrate the thinning zona pellucida. If fertilization takes place, the zona pellucida disappears, to permit implantation in the uterus.

The zona pellucida supports communication between oocytes and follicle cells during oogenesis; protects oocytes, eggs, and embryos during development, and regulates interactions between ovulated eggs and freeswimming sperm during and following fertilization.

Q3. Marble bone disease (2 marks)

Osteopetrosis or Marble bone disease

Osteopetrosis is a bone disease that makes bones abnormally dense and prone to breakage (fracture). This disorder is characterized by increased bone density and abnormal bone growth.

Marble bone disease, also called osteopetrosis or Albers-Schönberg disease, rare disorder in which the bones become extremely dense, hard, and brittle. The disease progresses as long as bone growth continues; the marrow cavities become filled with compact bone. Because increased bone mass crowds the bone marrow, resulting in a reduced amount of marrow and therefore a reduced capacity to produce red blood cells, severe anemia results

Q4. Bone precursor cell (2 marks)

During intramembranous ossification in the skull, neural crest derived mesenchymal cells proliferate and condense into compact nodules. Some of these cells develop into capillaries; others change their shape to become osteoblasts, committed bone precursor cells.

What happens when fusion occur between sperm and egg 2 marks

Recognition of sperm by the vitelline envelope or zona pellucida is followed by the lysis of that portion of the envelope or zona in the region of the sperm head by the acrosomal enzymes. This lysis is followed by the fusion of the sperm plasma membrane with the plasma membrane of the egg. The sperm and egg plasma membranes then join together, and material from the sperm membrane can later be found on the egg membrane. The sperm nucleus and tail pass through the resulting cytoplasmic bridge, which is widened by the actin polymerization.

The process of fertilization involves a sperm fusing with an ovum. After the sperm enters the cytoplasm of the oocyte (also called ovocyte), the tail and the outer coating of the sperm disintegrate and the cortical reaction takes place, preventing other sperm from fertilizing the same egg. The oocyte now undergoes its second meiotic division producing the haploid ovum and releasing a polar body. The sperm nucleus then fuses with the ovum, enabling fusion of their genetic material. The successful fusion of gametes forms a new organism

Q5. Fertilin function (2 marks)

In mammals, the fertilin proteins in the sperm plasma membrane are essential for sperm membraneegg membrane fusion Mouse fertilin is localized to the posterior plasma membrane of the sperm head. It adheres the sperm to the egg by binding to the 6β1 integrin protein on the egg plasma membrane fertilin appears to bind the sperm plasma membrane to the egg plasma membrane and then to fuse the two of them together. When the membranes are fused, the sperm nucleus, mitochondria, centriole, and flagellum can enter the egg Fertilin is a sperm surface protein with an essential role in fertilization. It is required for the migration of spermatozoa through the oviduct, for binding to the zona pellucida, and for efficient binding to the egg plasma membrane

Q6. Function of dynein (2 marks)

The core of the axoneme consists of two central microtubules surrounded by a row of nine doublet microtubules. The force for sperm propulsion is provided by dynein, a protein that is attached to the microtubules. Dynein hydrolyzes molecules of ATP and can convert the released chemical energy into the mechanical energy that propels the sperm.

Q7. Blastomere progress (2 marks)

Blastomeres generally progress through a cell cycle consisting of just two steps: M (mitosis) and S (DNA synthesis).

Q8. Embryonic shield (2 marks)

The cells of both the epiblast and hypoblast intercalate on the future dorsal side of the embryo to form a localized thickening, the embryonic shield.

Also called embryonic shield. in the early embryo of mammals, the flattened inner cell mass that arises at the end of the blastocyst stage and from which the embryo begins to differentiate.

Q9. Example of enhancer in human (2 marks)

The human β-globin gene has an enhancer in its 3´ UTR, roughly 700 base pairs 10.

What is homology of Hox genes in droshophila and of mammals 2 marks

The homology of gene structure and the similarity of expression patterns between Drosophila and mammalian Hox genes suggests that this patterning mechanism is extremely ancient. 11.

Process of neural crest

several other cell types. The Neural Crest

A group of ectodermal cells that gives rise to the spinal ganglia and various structures of the autonomic nervous system. The neural crest cells originate at the dorsal most region of the neural tube. The neural crest can be divided into four main functional (but overlapping) domains.

The cranial (cephalic) neural crest, whose cells migrate dorsolaterally to produce the craniofacial mesenchyme that differentiates into the cartilage, bone, cranial neurons, glia,and connective tissues of the face. Major pathways in

differentiation of neural crest

The trunk neural crest, whose cells take one of two major pathways.

Neural crest cells that become the pigment-synthesizing melanocytes migrate dorsolaterally into the ectoderm and continue on their way toward the ventral midline of the belly. The second migratory pathway takes the trunk neural crest cells ventrolaterally through the anterior half of each sclerotome. Sclerotomes are blocks of mesodermal cells, derived from somites, that will differentiate into the vertebral cartilage of the spine. The vagal and sacral neural crest, whose cells generate the parasympathetic (enteric) ganglia of the gut. The vagal (neck) neural crest lies opposite chick somites 1-7, while the sacral neural crest lies posterior to somite 28. The cardiac neural crest is located between the cranial and trunk neural crests. The cardiac neural crest cells can develop into melanocytes, neurons, cartilage, and connective tissue (of the third, fourth, and sixth pharyngeal arches). 12.

Causes in the activity cyclin of MPF

Mitosis-promoting factor contains two subunits.

The large subunit is called cyclin B. Small subunit of MPF, the cyclin-dependent kinase

Cyclin B is often encoded by mRNAs stored in the oocyte cytoplasm, and if the translation of this message is specifically inhibited, the cell will not enter mitosis. The presence of cyclin B depends upon its synthesis and its degradation. Cyclin B regulates the small subunit of MPF, the cyclin-dependent kinase.

Q13. Difference between Enhancer and Promoter?

An enhancer is a sequence of DNA that functions to enhance transcription. A promoter is a sequence of DNA that initiates the process of transcription. A promoter has to be close to the gene that is being transcribed while an enhancer does not need to be close to the gene of interest.

14.

Mode of commitment

Three basic modes of commitment are, ❖ Autonomous specification ❖ Conditional specification ❖ Syncytial specification 15.

What is sea urchin larva name 2 marks

Pluteus larve 16.

Cleavage in sea urchin

As the 16-cell embryo cleaves, the eight mesomeres divide to produce two "animal" tiers, an1 and an2, one staggered above the other. The macromeres divide meridionally, forming a tier of eight cells below an2. 17.

How neural groove form

Shortly after the neural plate has formed, its edges thicken and move upward to form the neural folds, while a Ushaped neural groove appears in the center of the plate, dividing the future right and left sides of the embryo. 18.

Retinoic acid foundation 3 marks

The specification of the ventral neural tube appears to be mediated by external tissues. One agent of ventral specification is the Sonic hedgehog protein, probably originating from the notochord. Another agent specifying the ventral neural cell types is retinoic acid, which probably comes from the adjacent somites. 19.

What is hierarchical development 3 marks

The developmental hierarchy is the hierarchical series of decisions involving specific preexisting cell types. These developmental decisions are usually irreversible, that progressively and irreversibly restrict cell fate. Animal development is the division of embryo into the three germ layers. 1. Ectoderm

2. Mesoderm
3. Endoderm

20.

periosteum 3 marks

the entire region of calcified spicules becomes surrounded by compact mesenchymal cells that form the Periosteum (a membrane that surrounds the bone).

The periosteum is a membrane that covers the outer surface of all bones, except at the joints of long bones. Endosteum lines the inner surface of the medullary cavity of all long bones. 21.