Gene expression for bigger limbs

[Silicon Waffle]

Take for example a fetus of 2 weeks old and a baby of 2 years old. The fetus doesn't show any limbs, skull. How do I know that is a human fetus ?

 

[Ryan_m_b]

By the time an embryo forms into a foetus the head, arms and legs are all present (in healthy cases). What is the basis for your question?

 

[Silicon Waffle]

Oh so sorry for my incorrect developmental stage, I should have meant the embryo
http://embryo.soad.umich.edu/carnStages/allStagesButtons.gif

The baby will not have any legs after 2 weeks (14 days). How could you identify whether it's either a human or some animal embryo given that you are not allowed to wait till it becomes bigger ?

 

[Ryan_m_b]

DNA testing would reveal what species it is. I have to ask though under what circumstances do you envision being given a random embryo and asked to identify the species?

 

[Silicon Waffle]

DNA testing would reveal what species it is. I have to ask though under what circumstances do you envision being given a random embryo and asked to identify the species?

Thanks Ryan_M_B.
I am learning how to identify species in each developmental stage. I don't know what genes expressed to grow a limb in the embryo and because a tiny embryo still doesn't have all genes like an adult does, DNA barcoding so may not work. I don't know if that is true.

 

[Ryan_m_b]

From the moment an egg is fertilised it has all the genes it is ever going to have. Adults, babies, foetuses and embryos all have the same genes. The difference is in the expression of those genes, both in time and space. Simply put when a gene is expressed it is "on", when it is not expressed it is "off". A nerve cell has the same genes as a muscle cell but they express different genes making them different phenotypically. Good luck with your attempt, I'm not sure how easy it is to differentiate species by looking at their foetuses, especially in the early stages.