20.1-20.4

Question 1

homeotic mutations

Answer 1

a mutant in which an apparently normal organ or body part develops in the wrong place

Question 2

totipotent

Answer 2

a property of embryonic cells

means they have the potential to differentiate into any tissue or cell type the animal can produce.

all genes have the potential to be expressed given the appropriate queues

Question 3

embryonic stem cells

Answer 3

totipotent cells of all early embryos in vertebrates

Question 4

differentiated

Answer 4

cells having taken on different morphologies and undertaking different physiological activities

Differentiation is characterized by hanges in the patterns of gene expression that progressively limit which genes continue to be expressed by each cell type.

Question 5

pluripotent

Answer 5

cells that have retained the potential to give rise to many different types of descendants, but not all.

Question 6

development

Answer 6

a progressive process during which totipotent cells differentiate into specialized cell types through a series of genetically controlled steps that place ever more restrictive limits on their developmental potential.

Question 7

positional information

Answer 7

inthe combinations of internal and external signals that a cell perceives during development provides information on the cells location within an organism

Question 8

morphogens

Answer 8

substances whose presence in different concentrations directs developmental fates.

discreet boundaries can be established if activation or repression of gene expression is dependent on threshold concentrations of a morphogen

Question 9

induction

Answer 9

once a cell has acquired a specific identity, it may induce its neighbors to acquire a certain fate

Question 10

organizer

Answer 10

cells in an organizer region possess the ability to organize cells in the surrounding tissue.

Question 11

inhibition

Answer 11

a cell that acquires a specific fate may then produce an inhibitory substance that prevents its neighbors from acquiring a certain fate

can be used to produce patterns of regularly spaced cells of a particular fate within a field of cells that would otherwise all differentiate in the same manner.

Question 12

syncytium

Answer 12

early in embryonic development in Drosophila proceeds by nuclear division without division of cytoplasm, forming a syncytium.

A multinucleate cell in which the nuclei are not seperated by cell membranes.

Question 13

syncytial blastoderm

Answer 13

after syncytium formation from nine mitotic nuclear divisions, the nuclei migrate to the periphery of the embryo. Then about 10 pole cells, from which the germ line will be derived are set aside at the posterior end of the embryo.

the somatic cells undergo another four rounds of mitotic divisions at the periphery, forming a syncytial blastoderm containing about 6000 nuclei.

Question 14

cellular blastoderm

Answer 14

by about 3 hours after egg laying, cellularization of the syncytium occurs by the assembly of cell membranes that seperate nuclei into individual cells, thus forming a cellular blastoderm.

cells already have become committed to differentiate into particular tissues when the cellular blastoderm has been formed.

Question 15

housekeeping genes

Answer 15

genes that have essential cellular functions, mutations result in lethality.

Question 16

coordinate genes

Answer 16

defects affect an entire pole of the larva

Question 17

gap genes

Answer 17

mutants are missing large contiguous groups of segments

Question 18

pair-rule genes

Answer 18

mutants are missing part of adjacent segment pairs in alternating segments

expression follows that of gap genes and produces seven stripes in the embryo (for Drosophila)

Question 19

segment polarity genes

Answer 19

defects affect patternng within each of the 14 segments

occurs in 14 polar stripes (i.e. each stripe has anterior and posterior “poles”) one for each embryo segment

Question 20

homeotic genes

Answer 20

defects affect the identity of one or more segments

last genes to be expressed

affect broad domains of contiguous parasegments along the anterior-posterior axis.

Question 21

parasegments

Answer 21

domains of gene expression controlled by the pair-rule gene

expression

Question 22

maternal effect genes

Answer 22

in animals, the mother often supplies critical gene products to the egg tat subsequently direct embryo development.

the genotype of the mother determines the phenotype of the zygote

Question 23

zygotic genes

Answer 23

genes that are only active in the zygote or embryo.

for these genes, the genotype of the embryo determines the phenotype.

Question 24

Antennapedia complex

Answer 24

consists of five genes
one of two homeotic clusters on the third chromosome for Drosophila

(mutants have legs on head)

Question 25

bithorax complex

Answer 25

consists of 3 genes

one of two homeotic clusters on the third chromosome for Drosophila

Question 26

homeobox

Answer 26

all Homeotic genes share a conserved sequence of DNA of 180 nucleotides called the homeobox, encoding a 60-amino acid protein domain, termed the homeodomain.

Question 27

homeodomain

Answer 27

has a helix-turn-helix motif. made

Question 28

Hox genes

Answer 28

homeobox genes that share both molecular and functional similarity as well as having a common evolutionary origin

Question 29

realizator genes

Answer 29

genes whose expression is determined by the parasegment the cell is contained in.

They are expressed with the right combination of Hox gene expression

Question 30

inductive signal

Answer 30

a molecule produced by a cell controlling differentiation.

If it is disseminated in a gradient, the cell closest to the anchor cell could acquire a different fate than cells that are more distant.

Question 31

lateral inhibition

Answer 31

applies to inductive signaling
after the reception of a signal, a second signal is sent to another cell that inhibits other cells from differentiating the same way as the cell receiving the signal. It reinforces initial asymmetry.

Question 32

co-option

Answer 32

a common theme in the evolutionary history of all genes, and particularly those influencing development, is the co-option of genes and genetic modules to direct the patterning or growth of novel organs.

Question 33

evo-devo

Answer 33

the study of the evolution of development

Question 34

zone of polarizing activity (ZPA)

Answer 34

acts as an organizer that promotes digit formation at the distal ends of lim buds through the production of a morphogen, now known to be a small secreted signaling protein called sonic hedghog (shh).