Embryology Concepts

Question 1

Describe the three different approaches to the study of embryology

Answer 1

Anatomical: observing change over time
Experimental: interaction through causing change and observing
Genetic: looking at the impact of small genetic and DNA based changes

Question 2

Define ontogeny

Answer 2

The study of the sequence of events involved in an individual organism’s development during it’s own lifetime.

Question 3

Define phylogeny

Answer 3

The study of the sequence of events during the evolution of a species throughout multiple generations.

Question 4

Define metamerism

Answer 4

The development of an organism into subdivisions of the embryonic body into ordered series of equal segments (metameres). e.g. Worms, insects, axial body of humans

Question 5

Von Baer’s 1st law

Answer 5

1. General features of large groups of animals appear earlier in development than the specialized features of small groups of animals.

Question 6

Von Baer’s 2nd law

Answer 6

Less general characters develop from more general characters until finally the most specialised appear e.g. Nasal structures in all mammals are developed very generally early on and only later do they specify the features specifically suited to that species.

Question 7

Von Baer’s 3rd law

Answer 7

The embryo of a given species, instead of passing through the adults staged of lower animals, departs more and more from them.

Question 8

Von Baer’s 4th law

Answer 8

Therefore, the early embryo of a higher animal is never like a lower animal, but only like it’s early embryo.

Question 9

Define somitogenesis

Answer 9

The making of somites, structures on either side of neural tubes which associate with specific spinal nerves and innervate any nerves derived from these specific somites.

Question 10

Define mesoderms

Answer 10

Presomites - structures developing into somites which give rise to vertebrae.

Question 11

Define ectoderm

Answer 11

The covering of skin

Question 12

Explain the Hox Code

Answer 12

The family of genes (hox genes) first identified in drosophila which is found in all vertebrae. Hox genes are expressed in a very specific pattern and allow definition of segments by combining within each section and therefore dividing the neurotube.

Question 13

Explain the Organiser

Answer 13

(Found in all vertebrate embryos) when taken from a pigmented embryo and grafted to the ventral side of an unpigmented host embryo, it induces an extra embryonic axis and a new neural tube, thus leading to the formation of a second embryo that is linked to the host.