Chapter 18

Question 1

Development is ____________________________. The key to understanding development is to understand how ____________________________________ impact cell differentiation and specialization

Answer 1

the building of a multicellular organism, different patterns of gene expression

Question 2

T or F: reverse genetics approach identified most of the genes involved in development

Answer 2

False, forward genetics did.

Question 3

What are the three fundamentals of development?

Answer 3

(1) Cell differentiation
(2) Positional information (gradient model)
(3) Pattern formation (body-plan axes)

Question 4

Explain Cell Differentiation

Answer 4

A single-celled zygote undergoes several mitoses, becoming a cluster of embryonic stem cells which eventually divide and differentiate

Question 5

T or F: in adult animals, most cells have differentiated and are locked into that cell type but there are exceptions with pluripotent stem cells that can be differentiated into a limited number of cell types

Answer 5

True

Question 6

Explain Positional Information

Answer 6

all cells have the potential to differentiate into the same fate but this differentiation can depend on the concentration of a morphogen along a gradient

Question 7

Morphogens

Answer 7

substances whose presence in different concentrations determines developmental fates

Question 8

How are morphogen gradients formed?

Answer 8

1) dividing cellular contents within cells
2) asymmetric cell divisions - daughter cells inherit distinct subsets of the factors present in the original cell

Question 9

Explain Pattern Formation

Answer 9

the interacting events that organize differentiating cells to establish the body-plan axes: anterior-posterior, dorsal-ventral, left-right.

Question 10

Organizers are cells…

Answer 10

that determine their neighbors identity and fate

Question 11

Induction VS Inhibition

Answer 11

Induction: induces the neighboring cells to adopt a specific fate
Inhibition: prevents its neighbors from adopting a certain fate

Question 12

In Drosophila larvae, what are the five classes of mutations that influence Drosophila development?

Answer 12

1) Coordinate Genes: defects affect an entire pole of larvae
2) Gap Genes: mutants are missing large, contiguous groups of segments
3) Pair-rule Genes: mutants are missing parts of adjacent segment pairs, in alternating patterns
4) Segment polarity Genes: defects affect patterning within each of the 14 segments
5) Homeotic (Hox) Genes: defects affect the identity of one or more segments

Question 13

In Drosophila, there are two homeotic clusters on the third chromosome: the ______________ complex (3 genes) and ___________ complex (5 genes) - the order of theses genes reflects the positions along the anterior-posterior axis

Answer 13

Bithorax, Antennapedia

Question 14

T or F: in drosophila larvae, segment-polarity genes activate gap gene expression patterns and they both determine expression patterns of pair-rule and coordinate genes - individual segments acquire their unique identities through Hox genes

Answer 14

False, segment-polarity and coordinate genes are switched.

Question 15

How are human digits determined?

Answer 15

All tetrapod’s are characterized by five or fewer digits per set, with each digit having its own unique identity, specified by hox gene expressions

Question 16

4 Mutations that Alter Digit Formation
1) Ectopic…
2) Mutations that…
3) Separation of…
4) Loss of…

Answer 16

(1) Ectopic expression of Hoxd genes can alter digit identity
(2) Mutations that expand or increase expression of Shh gene (upstream of Hoxd genes) result in formation of extra digits
(3) Separation of the limb bud into individual digits in humans requires programmed cell death between the digits
(4) Loss of limbs in snakes/cetaceans is due to alterations in Hox and/or Shh gene expression

Question 17

T or F: roundworms are free-living transparent animals, adult males have roughly 1031 cells while adult hermaphrodites have roughly 959 cells, they have a lifespan of 2-3 weeks and a generation time of 3-4 days. They have five pairs of autosomes and one pair of sex chromosomes (Males: XO, Hermaphrodite: XX)

Answer 17

True

Question 18

How does a roundworm’s vulva develop?

Answer 18

The vulva forms during the last larval stage, from six precursor cells (VPCS, P3 to P8) - 3 actually give rise to structures of the vulva itself (primary cell and sides on either side are secondary cells)

Question 19

Lateral Inhibition

Answer 19

once a lin-3 signal is received by the primary cell, a second signal is sent that inhibits neighboring cells from becoming primary cells

Question 20

Primary Cell Induction

Answer 20

the anchor cell has the lin-3 gene which encodes a small, secreted protein that acts as the signaling molecule for primary cell

Question 21

Plants represent an independent event in multicellular evolution and the two major differences between animals and plants are…

Answer 21

1) animals have early separation of germ cells
2) plants can add new organs after maturity

Question 22

Meristems

Answer 22

pluripotent cells in plants, there are root meristems and shoot meristems (leaf, axillary, and reproductive meristems)

Question 23

How is plant flower development genetically controlled?

Answer 23

ABC Model

Question 24

Arabidopsis thaliana is a model plant for genetics research, they are composed of 4 concentric whorls of organs:

Answer 24

sepals, petals, stamens, carpels.

Question 25

For the ABC model, what does the A, B, and C genes encode for?

Answer 25

Sepals: A
Petals: A + B
Stamens: B + C
Carpels: C

Question 26

Describe the 3 classes of mutations in Arabidopsis

Answer 26

A) carpels (1/4) & stamens (2/3)
B) carpels (3/4) & sepals (1/2)
C) sepals (1/4) & petals (2/3)

Question 27

ABC genes act as ________________ and contain the homeotic ____________. These _____________ genes are not related to Hox genes in animals.

Answer 27

transcription factors, MADS box, MADS box