ch 21.4-5: genes and development

Question 1

what 3 axes build the body plan?

Answer 1

1. anterior to posterior
2. dorsal to ventral
3. left to right

Question 2

how do cells know where they are in a developing embryo?

Answer 2

by different signal molecules present at different concentrations along each of the axes

Question 3

how is information from signaling molecules transmitted?

Answer 3

through receptors and signal transduction cascades that activate transcription factors

Question 4

what is a result of signals changing with time and position?

Answer 4

distinct transcription factors turn genes on or off, and the patterns of gene expression during stages of development determine the fate of each cell

Question 5

pattern formation

Answer 5

series of events that determines the spatial organization of an entire embryo or parts of an embryo

Question 6

what types of molecules are involved in pattern formation?

Answer 6

a molecule that signals a target cell is in one of the 3 axes

Question 7

what do pattern formation molecules exist in?

Answer 7

concentration gradient

Question 8

morphogen

Answer 8

embryonic cells that exist in a concentration gradient and use this information to determine their location

Question 9

what is set up by morphogens?

Answer 9

the 3 axes

Question 10

what do genes activated by morphogens do?

Answer 10

turn on other genes that generate new signal molecules that provide more specific information about the parts of the body

Question 11

in drosophila, how are body axes set up?

Answer 11

they are laid down in the egg before fertilization
- made by the genes in the mother

Question 12

maternal effect mutations

Answer 12

a mutation in the female parent that alters the phenotype of the offspring without causing an obvious mutated phenotype in the parent

Question 13

body segments

Answer 13

well-defined body region that is repeated along the anterior-posterior body axis in an animal

Question 14

what do body segments produce?

Answer 14

body structures such as wings, legs, and antennae

Question 15

bicoid

Answer 15

regulatory transcription factor that binds to enhancers in DNA and activates genes required for the formation of anterior structures

Question 16

bicoid mutation

Answer 16

posterior segments formed at the anterior segments
- headless

Question 17

in situ hybridization

Answer 17

technique used for detecting where mRNAs are in cells and tissues by use of labeled complementary probes

Question 18

in situ hybridization process

Answer 18

1. obtain single-stranded DNA or RNA probe complementary to target mRNA
2. add fluorescent label to probe
3. add copies of probe to preserved cells of embryo
4. probe binds to complementary target of mRNA

Question 19

where was the bicoid mRNA found?

Answer 19

higher concentration in the anterior region

Question 20

if there are higher levels of bicoid, what does that tell a cell?

Answer 20

that it is in the anterior region

Question 21

if there are low concentrations of bicoid, what does that tell a cell?

Answer 21

that is in the posterior region

Question 22

genetic regulatory cascades

Answer 22

set of regulatory genes that are linked in a way that one initially activated gene turns on the expression of other regulatory genes, which trigger the expression of more regulatory genes

Question 23

genetic regulatory cascade in drosopila

Answer 23

1. Maternal Effect Genes
2. Gap Genes
3. Pair-Rule Genes
4. Segment Polarity Genes
5. Hox Genes
6. Effector Genes

Question 24

hox genes

Answer 24

specify which adult structures will develop from each segment in the mature organism

Question 25

what do hox genes code for?

Answer 25

transcription factors that activate the expression of effector genes that lead to the production of particular proteins that create differentiated cells

Question 26

how are hox genes presented?

Answer 26

in clusters along a single chromosome

Question 27

what does the order of hox genes correspond to?

Answer 27

the order of where the genes are expressed along the anterior-posterior region

Question 28

homeotic mutation

Answer 28

mutation that causes the wrong body part to form in the wrong place

Question 29

what do hox genes contain?

Answer 29

homeobox: DNA sequence that codes for the DNA-binding domain of a hox-encoded transcription factor

Question 30

are hox genes used multiple times?

Answer 30

yes, through different stages of development

Question 31

hoxB6 gene

Answer 31

gene sequence found in mice that is similar to the Antp gene of flies - specifies leg development

Question 32

what happen when the hoxB6 gene was inserted into drosophila?

Answer 32

it replaced the fly's antennae with legs

Question 33

what does the hoxB6 insertion in mice show?

Answer 33

that hox clusers of animals are homologous - similar because they descended from genes in a common ancestor

Question 34

tool kit genes

Answer 34

conserved set of genes that code for signal proteins, signal-transduction pathway components, and transcription factors

Question 35

are hox genes considered tool kit genes?

Answer 35

yes

Question 36

what allows tool kit genes to be used in new ways?

Answer 36

mutations

Question 37

what happens if developmental processes are disrupted?

Answer 37

the embryo is likely to die

Question 38

heterometry

Answer 38

altered quantity of gene expression of a developmental gene

Question 39

heterochrony

Answer 39

altered timing of gene expression of a developmental gene

Question 40

heterotropy

Answer 40

altered spatial pattern of gene expression of a developmental gene