Expert: Dana Krempels, Ph.D. - 10/7/2009

Question
QUESTION: hi, wondering if you could settle this for me please. A cell consist of 3 layers the ectoderm, mesoderm and the endoderm while also been made up of nucleus, protoplasm and membrane and not forgetting DNA and RNA. i was wondering is that everything that decides our design instructions.
please and thanks and just so you know this is not a homework question just an on going debate I'm having with my brother

ANSWER: Dear Claire,

A cell does not consist of endoderm, ectoderm and mesoderm.  Those three tissues are embryonic "germ layers" that comprise the early embryo of an animal, and each is made up of cells.

A single cells formed from two fused gametes is known as a zygote.  Following the instructions in the DNA inside the nucleus, the zygote divides in an orderly fashion to become an embryo.  You can see this progression here:

http://www.bio.miami.edu/dana/pix/gastrulation.jpg

The last picture in the series shows an embryo that has "caved in" to form an early gut which is lined by the yellow-coded endoderm.  The blue tissue on the outside is ectoderm.  Later, in some animals, a middle layer of mesoderm will develop, usually derived from the endoderm.

Hope that helps your debate!

Dana

---------- FOLLOW-UP ----------

QUESTION: thanks  so is it just the dna that gives an infant their design instruction or is it something else

Answer
Dear Claire,

Any embryonic organism is directed in its growth and development by the instructions encoded in its DNA.  However, environment can also play a significant role by affecting how the genes (on the DNA) are expressed, and when.

So any organism is a product of both "Nature" (DNA) and "Nurture" (environmental influence).

Hope that helps.

Dana