A questionnaire is defined as a document containing questions and other types of items designed to solicit information appropriate for analysis. The questionnaire may be regarded as a form of an interview on paper. Procedure for the construction of a questionnaire follows a pattern similar to that of the interview schedule. However, because the questionnaire … Read more Questionnaire- Types, Format, Questions
The nematode worm Caenorhabditis elegans is a small (1 mm long), unsegmented, vermiform, free-living soil nematode. It is a relatively simple, and precisely structured organism, extensively used as a model organism for molecular and developmental biology. The body of an adult C. elegans hermaphrodite contains exactly 959 somatic cells, whose entire lineage has been traced through its … Read more Development of Caenorhabditis elegans
A simple description of the health status of a community, based on routinely available data or on data obtained in special surveys, is often the first step in an epidemiological investigation. Such a study is termed as a descriptive study. A descriptive study – as the name implies – describes the distributions of disease, injury or health in a … Read more Descriptive Studies- Types, Applications, Advantages, Limitations
The preimplantation period of human embryo development is remarkable and characterized by successive changes in terms of genetic control, physiology, and morphology of the embryo. Blastocyst (Greek, blastos= sprout + cystos = cavity) is a distinctive stage of mammalian embryo development, characterized by a hollow cellular mass that forms in early development. It is an embryo that has developed for … Read more Blastocyst- Stages, Significance
DNA methylation is a process by which methyl groups are added to the DNA molecule. It is an epigenetic mechanism that occurs by the addition of a methyl (-CH3) group to DNA, thereby often modifying the function of the genes and affecting gene expression. The most widely characterized DNA methylation process is the covalent addition of the methyl group at the 5-carbon of … Read more DNA Methylation
All epidemiological studies are mostly attempting to establish the presence or absence of a causal relationship, and the results are an estimate of the actual effect or degree of association. All studies are subject to error, which can obscure or minimize the truth- the size and nature of a causal relationship. Understanding common errors and … Read more Error- Types, Sources and Control
‘Embryo transfer’ refers to the transplantation of a mammalian preimplantation embryo into the reproductive tract of a recipient female so that it may implant and continue to develop to birth. Mammalian embryos of many species can develop in vitro from fertilization to the blastocyst stage (approximately 100 cells), but at this point, they must implant in the … Read more Human Embryo Transfer
Human Embryogenesis Human embryogenesis refers to the development and formation of the human embryo. It encompasses the first eight weeks of development after fertilization, in which a single cell formed at fertilization turns into an organism with a multi-level body plan. It is characterized by the process of cell division and cellular differentiation that occurs during the early stages … Read more Human Embryogenesis
The most characteristic event occurring during the third week of gestation is gastrulation. Gastrulation is a formative process by which the three germ layers, which are precursors of all embryonic tissues, and the axial orientation are established in embryos. During gastrulation, the bilaminar embryonic disc is converted into a trilaminar embryonic disc. Extensive cell shape … Read more Gastrulation- Process, Consequences
Comparative embryology is the branch of embryology that compares and contrasts embryos of different species, showing how all animals are related. Put simply, comparative embryology is the comparison of embryo development across species. All vertebrate embryos follow a common developmental path due to their common ancestry. They pass from single cells to multi-celled zygotes, clumps of cells called morulas, and hollow … Read more Comparative Embryology- Principle, Significance
