21) ZPA cells of the chick embryo produce which morphogen?

A) sonic hedgehog

B) sonic chicken

C) bicoid

D) chicken wing factor

22) How long is the DNA in the homeobox sequence?

A) 4 base pairs

B) 68 base pairs

C) 180 base pairs

D) 362 base pairs

23) What is the significance of the homeobox sequence studied in animal species?

A) Certain genetic instructions for development have changed very little over time.

B) Certain genetic instructions for development have changed a great deal over time.

C) Certain genetic instructions vary based on structural differences.

D) Certain genetic instructions vary based on phyla.

24) Predict what would happen if a fruit fly regulatory gene that codes for a leg replaced a frog gene in the same position.

A) The frog would produce a fruit fly leg.

B) The gene would kill the frog embryo.

C) The frog would produce a frog leg.

D) The frog would produce a leg that is part frog and part insect.

25) Two populations of cells may end up segregating themselves into different layers during development because they have different:

A) DNA.

B) sizes.

C) apoptosis programming.

D) phospholipid molecules.

E) cell adhesion molecules.

26) What action by the individual cells involved can assist processes involving cell movement such as gastrulation?

A) transcription factors

B) microfilament growth

C) invagination

D) evagination

E) phagocytosis

27) Without programmed cell death, your ________ might look more like a ________.

A) hand; paddle

B) head; hand

C) leg; heart

D) foot; hoof

28) Development occurs:

A) throughout the life of the organism.

B) only in non-dividing cells.

C) only during growth of the organism.

D) only in animals.