Chapter 18: Developmental Genetics

Question 1

What are the three fundamental principles of development?

Answer 1

Timing, location, and integration of both.

Question 2

What is positional information?

Answer 2

Morphogen gradients that determine cell fate based on concentration.

Question 3

What is induction in development?

Answer 3

Cells signal neighbors to adopt specific fates.

Question 4

What is inhibition in development?

Answer 4

Cells prevent neighbors from adopting certain fates.

Question 5

Which RNAs establish the anterior-posterior axis in Drosophila?

Answer 5

Bicoid (anterior) and Nanos (posterior).

Question 6

How do Bicoid and Nanos proteins act?

Answer 6

They diffuse to form opposing gradients.

Question 7

What establishes the dorsal-ventral axis?

Answer 7

Dorsal protein activated by Spaetzle-Toll signaling.

Question 8

What does phosphorylated Dorsal do?

Answer 8

Enters nucleus and regulates ventral-specific genes.

Question 9

Name the five classes of segmentation genes.

Answer 9

Coordinate, gap, pair-rule, segment polarity, homeotic.

Question 10

What is the role of homeotic genes?

Answer 10

Assign segment identity.

Question 11

What happens in Ubx mutants?

Answer 11

Halteres transform into wings.

Question 12

What happens in Antennapedia mutants?

Answer 12

Antennae transform into legs.

Question 13

What is a homeodomain?

Answer 13

Helix-turn-helix DNA-binding motif in homeoproteins.

Question 14

What is a master regulatory gene?

Answer 14

A gene controlling major developmental programs (often TF).

Question 15

Example of a master gene in eye development?

Answer 15

Eyeless in flies; Pax6 in vertebrates.

Question 16

What does ectopic expression of eyeless cause?

Answer 16

Eye formation anywhere in the body.

Question 17

Mutation in Pax6 in humans causes?

Answer 17

Aniridia (no iris).

Question 18

What is Sonic hedgehog’s role?

Answer 18

Limb patterning; expressed in ZPA.

Question 19

Mutation in Shh in humans causes?

Answer 19

Polydactyly

Question 20

Why are developmental pathways conserved?

Answer 20

Shared evolutionary origin and similar regulatory logic.

Question 21

If a gap gene is mutated, what will the embryo look like?

a) it will miss the anterior end
b) A broad region of the embryo will be absent
c) Alternating segments will be missing

Answer 21

b) A broad region of the embryo will be absent

Question 22

Why do you think the bicoid RNA does not
diffuse, but the protein does?

A) RNA is too big
B) It is somehow kept at the anterior pole
C) Researchers do not know yet

Answer 22

B) It is somehow kept at the anterior pole

Question 23

What is the determining feature that allows the
establishment of the anterior-posterior axis?

A. protein diffusion
B. Tethering of mRNA
C. Two mRNAs that are tethered at opposite poles
D. All of these

Answer 23

D. All of these

Question 24

Why do flies with a mutation in Ultrabithorax (Ubx) have
two pairs of wings?

A. Because this homeotic mutation transforms T3 into T2
B. Because both segments have become T3 segments,
and the system can’t keep them apart.
C. Because of an aberrant signaling pathway
D. Because this mutation disturbs the pair-rule genes that
need to correctly set up T2 and T3.

Answer 24

A. Because this homeotic mutation transforms T3 into T2

Question 25

Which of these is not true about Homeoproteins? A. They are also called Hox proteins B. They are Master regulators C. The genes coding for them are called segment identity genes D. They are maternally deposited proteins that contain a homeodomain

Answer 25

D. They are maternally deposited proteins that contain a homeodomain

Question 26

Which of these does the Drosophila mother add to the egg? A. Activated Dorsal protein B. Homeodomain proteins C. bicoid protein D. Bicoid RNA

Answer 26

D. Bicoid RNA