12

You may want to look into "Evolutionary - Developmental Biology", which deals with how an embryo develops into a grown organism. Thus, by combinatorial specifying the identity of particular body regions, Hox genes determine where limbs and other body segments will grow in a developing embryo or larva. A paragon of a toolbox gene is Pax6/eyeless, ...


10

First of all, I should quote the sentence from the MOST reliable ophthalmology sourcing in the world - American Academy of Ophthalmology: Section 11 - "Lens and Cataract" "The equatorial diameter of the unfixed human lens measures 2 mm at 12 weeks and 6 mm at 35 weeks. Both the growth and the maturation of lenticular fibers continue throughout life." The ...


9

While it might make more logical sense to have separate passageways for air and food/water, this did not happen in evolutionary history due to the peculiarities of lung development. Vertebrate lungs develop as an outpouching of the gut tube, which itself has a very long evolutionary history (probably homologous among all deuterostomes). In the image below, ...


9

All animals develop in this way, whether they are oviparous (developing in an egg) or viviparous (developing inside their mother, or live-birth). From Wild Birds Unlimited: All mammals have navels or belly buttons where the umbilical cord distributes nutrients between a mother and her fetus. After birth, the umbilical cord is cut and a scar develops on ...


7

No. In fact the lens of the eye, which is nearly optically perfect in humans, does not change or grow after it is fully formed around week 26 of gestation. Interestingly this is why one of the cues for identifying young children is having small faces with large eyes. This also the case for puppies and cats and other animals, who are mostly cuter when they ...


7

The first differentiation in human embryogenesis is from early blastomeres into trophoblast, which forms the outer layer of the blastocyst, and inner cell mass (ICM). It may be unsurprising then that cells on the inside of the 8-16 cell stage morula differentiate into ICM whereas those on the outside differentiate into trophoblast. However it is currently ...


6

I wanted to add some helpful references. The 6th edition of the Gilbert Developmental Biology textbook is available on NCBI bookshelf. It's a bit old (2000), but much of the information is still relevant. You can search this textbook for specific terms but not browse. There is also a collaborative science/fashion project between the Storey sisters, called ...


6

Identical twins Twinning occurring at the two cell stage or afterwards, up to and including the 16 cell stage, which translates to days 1 to 3 after fertilization, results in diamniotic, dichorionic twins. Twinning at the 32 cell stage (day 4), up to and including day 6 results in diamniotic, monochorionic twins. The majority of identical twins split at ...


5

This is a very general question. The "developmental sequences" are just genes like any other. Like all genes they are semi-randomly distributed through the genome. While there are gene-rich and gene-poor areas in the genome, with some exceptions --notably the homeobox genes--, genes are not grouped by function. As to how they are accessed sequentially, that ...


5

We can be sure it's a tail because it is an extension of the vertebrae, and we define "tail" as an extension of the vertebrae, among other things. tail tāl/ noun: tail; plural noun: tails the hindmost part of an animal, especially when prolonged beyond the rest of the body, such as the flexible extension of the backbone in a vertebrate, ...


4

A few possible explanations are named in the Wikipedia article you link: Regarding spontaneous or natural monozygotic twinning, a recent theory posits that monozygotic twins are formed after a blastocyst essentially collapses, splitting the progenitor cells (those that contain the body's fundamental genetic material) in half, leaving the same ...


4

I think CT is an abbreviation for connective tissue. Some examples of its use in that fashion: http://en.wikipedia.org/wiki/Connective_tissue https://web.archive.org/web/20151024041339/http://www.vetmed.vt.edu/education/curriculum/vm8054/Labs/Lab5/Lab5.htm http://www.pitt.edu/~sshostak/biosci1450/hislec03.html


4

There are molecular motors but the frequency is a function of energy input (ATP); similar to the angular velocity dependence on amount of current in electrical motors. The concept of molecular motor may not be suitable for a clock like device. There are clocks based on genetic circuits, which produce stable oscillations. Examples include the circadian ...


4

No, it is not possible. The reason is the genetic imprinting, which takes place on the parental DNA in the egg and the sperm. Here small modifications are added to the DNA which marks them as silenced. So some genes are expressed from the mother (while the fathers copy is not expressed) and vice versa. There are even genetic diseases which are caused by ...


4

Yes it is real, in the sense that this protocol has been through a peer reviewed journal. Note that the embryo is developing outside the shell, not outside the egg. It is the fertilized egg that develops into the embryo. The shell only provides protection and allows exchange of gases. You can replace the shell with any other material that does the same job. ...


4

In human,the mesoderm doesnot develop from the endoderm or the ectoderm.It develops from epiblast of the bilaminar germ disc stage. During the week 3 of development, the epiblast of the disc invaginate and divide rapidly to form the cells of the endoderm.The division is rapid enough to replace the hypoblast layer. Even after the endodermal layer has formed,...


4

Developing symmetry is is just a matter of Homeotic genes creating axial patterning, genes that produce a chemical gradient across a cell or group of cells. This is how developing organisms orient individual cells, up, down, left, right, anterior, posterior, medial, lateral, are all just gradients of different chemicals, the cells can detect the difference ...


4

The measles vaccine uses an attenuated virus: one that has been modified to reduce virulence such that it is (hopefully) no longer harmful to the host but still retains the antigenic determinants to induce acquired immunity. Although in modern times rational attenuation by genetic engineering is becoming established [1], the traditional method involves ...


3

Yes, you are correct. You can read the wikipedia article about an embryo: An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the >time of first cell division until birth, hatching, or germination. In humans, it is called an >embryo until about eight weeks after fertilization (i.e. ten weeks after the last menstrual >...


3

The answer depends on two factors: The type of vector (virus) you are using How well your vector can be integrated. The bottom-line is that there is no guarantee the vector will work even if you start from the embyro. As far as I know, the problem of using vectors in general is that the vector you are using might not be integrated into the genome of the ...


3

Saccus simply means sac or bag and is is closed cavity. The lymph nodes develop from the structures, see this image: Superior cardinal vein (jugular vein) Jugular lymphatic sacs Right subclavian vein Axillary lymphatic sacs Left brachiocephalic vein Thoracic duct (bilateral) Lumbar lymphatic sacs Iliac lymphatic sacs The image is taken from this webpage,...


3

I am no expert on the topic, but according to an article published on the centenary of his study, it states that the microscopical structure and classification of these areas are in parallel to the evolutionary distinction between old and new cortical subdivisions. So as and when new subdivisions are deduced (based on its function, cytoarchitecture or the ...


3

Regarding option C: Although it is correct that testosterone is converted into DHT, it is the former, not the latter, which is responsible for differentiation of the mesonephric (a.k.a. Wolffian) ducts: Between 8 and 12 weeks, the initial secretion of testosterone stimulates mesonephric ducts to transform into a system of organs—the epididymis, vas ...


3

The upper limit of transparency time of zebrafishes is anywhere from two to three weeks for normal zebrafish for optimal high-resolution imaging. However, there is a modified species of Zebrafish called 'Casper' which is now the preferred zebrafish strain for studies in cancer and other research, because the length of transparency lasts into adulthood. ...


3

The animal is very suggestive for Dog whelk-like mollusc removed from its shell. I try to mark the organs, do not rely on these marks as an absolut. Testis Renal vein Gill Mantle Prostate Osphradium 10 and others - digestive and reproductive systems, cannot mark precisely. Digestive gland source for comparing etc


3

The short answer is that no, a zygote doesn't express all genes simultaneously. A zygote is like any other cell, in that it represents a distinct phenotype. And like any other cell, this phenotype is maintained by tight regulation of gene expression patterns. Check out this paper, for a nice description of the process of embryonic gene activation. An ...


3

When in doubt go back to definitions I say (as I am now). cytoplasmic determinants: regulatory molecules located in specific distributions around egg cytoplasm Induction: process by which the presence of one tissue influences the development of others positional information, signals cells about its relative position to other cells. hox genes ...


3

"Cytoplasmic localization" is a very general term and it means that something is present in the cytoplasm. For instance (hypothetical but there are known examples), you can say protein-X is localized to cytoplasm or the cytoplasmic localization of protein-Y is reduced upon phosphorylation. Similarly, there are terms like "nuclear localization", "ER ...


3

Sperm can already be generated using stem cells http://blogs.discovermagazine.com/d-brief/2016/02/25/scientists-grow-working-sperm-from-stem-cells/#.V-UADBV94o8 Also, heart, liver and kidney cells as well. http://www.popsci.com/scientists-grow-transplantable-hearts-with-stem-cells http://www.ncbi.nlm.nih.gov/pubmed/26458176 Full organs are still far. The ...


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