The study of the development of an embryo from fertilisation through to description as a foetus.

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Mesoderm vs Mesenchyme- what's the difference?

My embryology textbook states that mesoderm can exist as Mesenchyme or Epithelium. I'm not sure what 'epithelium' means. Here is a quote for context: Somatic, splanchnic, and somite mesoderm can ...
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What is the difference between the neural tube and the dorsal ventral cord?

I was wondering what the difference is between the neural tube and the dorsal ventral cord. I know that the neural tube forms during embryonic development from the ectoderm layer that folds inwards. ...
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why is the cleavage in frogs holoblastic and not meroblastic?

background information The cleavage of the frog embryo during the embryo development is holoblastic (complete cleavage). However when we look at yolk-rich eggs we see a cleavage pattern which is ...
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Cells of Zona pellucida

My textbook states: Blastocyst hatches out by lysis of Zona pellucida with the help of the enzyme strypsin, Later the cells of Zona pellucida gradually disappear. We know that Zona pellucida is ...
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Embryo development terms

I'm trying to couple the following terms: cytoplasmic determinants, induction, positional information, hox genes, pattern information, morphogenisis, determination and differentiation. I hope ...
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Impact of Alan Turing's approach to morphogenesis

Shortly before his untimely passing, the computing pioneer Alan Turing published his most cited paper The Chemical Basis of Morphogenesis (1952). The central question for Turing was: how does a ...
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How is bilateral asymmetry determined in embryonic development?

What are the mechanisms that ensure consistent left-right asymmetric placement of various internal organs (heart, liver, etc) or consistent left-right asymmetric development of paired organs (brain, ...
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How scientists can be confident that human embryo tail is really a tail?

From Wikipedia: Human embryos have a tail that measures about one-sixth of the size of the embryo itself. As the embryo develops into a fetus, the tail is absorbed by the growing body. How are ...
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Does a zygote express all genes?

If a zygote has all the cytoplasmic determinants and all the specific transcription factors, does that mean that all genes in the genome are expressed?
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Do both the Sperm and Egg must be at exactly 7.4 pH for fertilization?

I suddenly came across this article and it says that for human conception to occur both the sperm and egg must be at exactly 7.4 pH - not 7.0, nor 7.7 but 7.4. If conception depended on such exact ...
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Conjoined twins formation theory

is it theoretically possible to take two fertilized mammalian eggs and push them together to make conjoined twins? How about forming non-identical conjoined twins?
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Is the amount of blood same in the pulmonary and systemic foetal circulation?

We learn that the stroke volume is the same for the right and left side of the heart. So the amount of blood in either circulations should also be the same. (is it? I myself doubt this statement. As ...
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How only one follicle develops into graffian follicle?

I've studied that one out of many follicle develops into mature or graffian follicle. The fact which confuses me is that, since all follicles are in same ovary, close to each other with equal supply ...
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Is the thecal sac ectoderm?

The thecal sac, or dural sac, is the membranous sheath of dura mater that surrounds the spinal cord and the cauda equina. The thecal sac contains the cerebrospinal fluid in which the spinal cord ...
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Why are eggs “egg” shaped?

Is there a reason as to why chickens lay "egg" shaped eggs, as opposed to spherically shaped eggs (or a random shape)? <--- Main Question For extra points (actually just to add more words in ...
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conjoined twins mirror image explanation

why are conjoined twins sometimes symmetrical, like organs such as liver, stomach and heart are mirror image of each other? Can you give me a hypothesis that could somehow involve primitive streaks? ...
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What tools are used in animal cloning?

So I was reading up on articles to do a project about cloning but there were no places in the article where It states the tool used to take the gene out of the nucleus and insert it into plasmids ? ...
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Polar bodies fertilization

Suppose a sperm fertilized a 2nd polar body( haploid) is there a chance of somewhat normal development?
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What is the mechanism of folic acid deficiency and neural tube defects?

I am having difficulty finding the mechanism by which folic acid reduces the risk of neural tube defects. I know that it does so, but what in particular actually occurs with folic acid deficiency to ...
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heterolog bodysites development?

Would it actually be possible due to unhomogen distribution of growth factors in the growth of an embryo to develop conditions like Polydactyly only on one side of the body or in an even stranger ...
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Do birds have navels?

This picture shows the development inside a bird egg: This shows the connection of the embryo to the yolk sac. Does this mean birds have navels? And if so, what happens to the umbilical cord once ...
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How DNA programs the first cell in womb into a human [closed]

Sorry if you see me silly. I am just a programmer happens to be curious about biology... So far I understand how DNA make protein, how cell divides, how one composed of cells->tissues-> organs. ...
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Resources for similarity between embryos

Is there a scientific paper/reputable image resource out there which I can use that the embryos of different organisms (vertebrata) are similar in their early developmental stages(without falling into ...
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Unknown animal - What could it be?

It's the first time I use this website and I really need help because I'm totally stuck Now I'm in school, but I'm trying to prepare for the Olympics During the preparation, I found the issue on the ...
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Front versus back in animal anatomy [closed]

Throughout various species, there seems to be a clear distinction between the front and the back. The musculature of the front, when engaged, closes or curls up the body, protecting it, while the ...
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177 views

How late in a human pregnancy can a zygote split?

This page indicates that the first two days is "very early" for a zygote to split, and that conjoined twins are the result of an "extremely late" split: If the zygote splits very early (in the ...
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Zygote Implantation and Pregnancy Detection

In a normal pregnancy, the embryo (blastocyst) implants between 8-9 days after ovulation. My understanding is that it is able to implant because the fertilized embryo produces a hormone that triggers ...
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How often does parthenogenesis in mammals happen?

Probably everyone knows that mammals can't produce viable offspring by parthenogenesis. But there are reports of human chimeras (see: a human parthenogenetic chimaera) and it's known for mice to ...
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Why is polyploidy lethal for some organisms while for others is not?

Polyploidy is the multiplication of number of chromosomal sets from 2n to 3n (triploidy), 4n (tetraploidy) and so on. It is quite common in plants, for example many crops like wheat or Brassica forms. ...
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Is the blastocyst a coeloblastula?

A coeloblastula is that type of blastula which has a fluid filled cavity. Since the blastocyst of the mammals does too, can it be called a coeloblastula? My book however mentions the two as different, ...
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Does embryonic development mimic (partly at least) the evolution of organisms on earth?

What do we know about the forces/mechanisms which lead to this seemingly "fast forward" evolution stages of the embryo? What are the theories dealing with this idea?
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How does an embryo know where to grow limbs etc

For example you have a cell or already a bunch of cells. Those cell(s) divide and after several week you have a grown organism, for example a human with limbs, several different organs etc. However, ...
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Cytoplasmic determinants - protostomes and deuterostomes

Cytoplasmic determinants are spread unevenly in the egg, and so when embryo starts forming (cells start dividing), the determinants are also unequally divided between cell. This unequal distribution ...
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How long do zebra fishes remain transparent?

As larva, zebra fishes are transparent, at least up to 5-6 days. I wonder what would be the upper limit of the transparent period. This is of relevance considering purposes for imaging. The question ...
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which exact mechanism triggers the first cell differentiation after n divisions?

I would like to understand which mechanism triggers the first cell differentiation after n divisions. I read previous articles on SE and Wikipedia articles on cellular differentiation and ...
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Why is the threshold between human embryo and human fetus defined as 8 weeks after fertilization?

Why is the threshold between human embryo and human fetus defined as 8 weeks after fertilization? What's happening on the 8th week? Note: definition of embryo based on Wikipedia's current ...
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What are differences between formation of embryonic disc in chick and mammal embryo?

Exam question which got lowest average points in my university: 1/5 average. No markscheme available so my attempt below. I assume that embryonic disk prefers to germ disk such that Formation prefers ...
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Negative role of Placenta

How can a placenta turn hostile to the mother or fetus ? What are the abnormalities found during placental delivery ?
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Waste generation by embryo [closed]

How does an embryo produce waste products even when its organ systems are not developed fully ? How does the placenta identify or differentiate waste materials from embryo ? Which organelle or ...
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Is telomere shortening consistant over consecutive cell divisions from zygote to a differentiated cell?

Considering the complexity of embryogenesis, a temporal referance would be helpful to coordinate the developmental sequences during embryogenesis and fetal development which is to be completed within ...
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Development of vitreous humor

I have tried reading about development of vitreous humor but it is all very confusing. When does it first developed ? Does it renew itself ? Please provide reliable sources..
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If two definitive ovums are fused will they form an organism?

Pretend that somehow in a laboratory two definitive ovums (finished 2nd miotic divisions) are are fused together. Will they form a new species?
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Do primitive lymph nodes exist in 12th week embryo?

Someone told me that primitive lymph nodes do not exist during this week. However, others say they can. Here is a picture about inguinal lymph nodes from here. No primary lymph nodes are visible ...
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How are babies born without a brain?

In the United States, anencephaly occurs in about 1 out of every 10,000 births. There are several forms of this condition, wherein the forebrain is absent. The forebrain is host to most of the higher ...
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How many areas are there in Brodmann map?

I read Wikipedia claiming 52. I heard that this can be extended to 54. I see there is no limit of having more areas - just better understanding of the neuroblast migration and fibroblast too, ...
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Activation Of Embryonic Genome

Embryonic gene activation is a process by which the embryo begins to transcribe its newly formed genome.As the embryonic gene activation occurs during early stages the paternal genome may not have any ...
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What is Saccus in Embryology?

The word seems to be of German origin. I have it here Saccus lymphaticus inguinalis, Saccus lymphaticus jugularis, Saccus lymphaticus posterior, Saccus lymphaticus retroperitonaealis. I ...
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Roles of creatine and bilirubin in foetus circulation

I think they are not inputs from maternal placenta. I think they are the results of foetus metabolism. However, I do not understand it how and where exactly. What are the roles of creatine and ...
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Does our eyeball increase in size as we grow?

Does the size of the eye increase as we develop from the stage the complete eye first forms to infancy and then to adulthood ?