Week 8

Question 1

Epistasis

Answer 1

Epistatic interactions are assyed by comparing the phenotype of a double mutant organism with that of the singly mutant organism

Question 2

Epistasis criteria for the two mutations

Answer 2

Have related phenotypes

• growth control
• sex determination
• dorsal ventral axis determination

Work on a pathway that makes a distinct decision

• growth/non-growth
• male/female
• expression/non-expression

The two mutation have distinct/opposite phenotypes

• all males versus all females
• expression always ON versus always OFF
• Ventrilized versus dorsalized

Question 3

Reproduction and cell phenotypes

Answer 3

Sperm fertilizes an egg forming the zygote and zygotic genome. The cells divide, during early division the maternal information coming form the maternal genome is important.

zygote starts out as totipotent but as the cells divide they become differentiated into specific cell types

Question 4

Order of differentiation

Answer 4

Pluripotent cell undergoes determination to become a determined cell the determined cell will differentiate into a differentiated cell with a distinct identity (has an identity now we can excute to give rise to a cell with the identity)

Question 5

Body plan

Answer 5

Anterior posterior axis
the body plan is where cells will end up in the fully developed organisms

the cells are being assigned identities

this nucleus divides

Question 6

The nucleus divides

Answer 6

This gives rise to a single layer of cells called the blastoderm (5,000 cells) monolayer of periphery cells.

at this stage the cells know exactly what they are going to become

the anterior posterior axis has already been determined

Question 7

Number of genes involved in the body plan

Answer 7

120 genes associated with the determination of the anterior posterior axis is the segmentation of the body plan

Question 8

Genetic hierarchy regulating determination of the A-P

Answer 8

Maternal coordinate genes (bicoid and nanos)

Zygotic Gap genes (hunchback)

Pair rule genes (fushi tarazu)

Segment polarity genes

Homeotic selector genes antennapedia

Question 9

Maternal coordinate genes

Answer 9

determines the development of the axis

Question 10

Zygotic gap genes

Answer 10

regulates the expression of pair ruled genes

Question 11

Pair rule genes

Answer 11

determine the number of segments that will form

Question 12

Segment polarity genes

Answer 12

patterns the axis within each segment

Question 13

Homeotic selector gene

Answer 13

determine what the segments will become

Question 14

Maternal to zygotic genome (humans)

Answer 14

transition form a developmental program being run off of information provided by the maternal genome and placed in the egg to the information that’s going to be expressed from the zygotic genome

transition occurs at the first cleavage cycles

Question 15

Maternal to zygotic genome (drosophila)

Answer 15

transition occurs at the blastoderm stage

Question 16

Maternal effect screens

Answer 16

Create larvae that are homozygous for a DNA seuqence change and ask whether the DNA seuqence change affects the development of the zygote.

in a maternal screen establish a homozygous mother who cannot pass down info to her progeny

Question 17

Generation timing of maternal effect screen vs zygotic screen

Answer 17

Maternal screen: F4 embryo/ F3 homozygous mother

Zygotic screen: F3 dead embryo

Question 18

bcd/bcd mother vs bcd/bcd (lf)

Answer 18

bcd/bcd mother normal egg

bcd/bcd (lf) larva missing a head

Question 19

Body plan and the anterior posterior axis

Answer 19

coordinate genes determine the basis axis of the head.

bicoid mRNA is located at the future anterior end of the egg, nanos is at the posterior end

Question 20

Nanos located in the posterior end

Answer 20

Nanos is required to surpress HB protein expression.

HB is present in the anterior end

nanos (lf) results in HB being expressed in both axis: development of larvae lacking abdominal segments

Question 20

Nanos located in the posterior end

Answer 20

Nanos is required to surpress HB protein expression.

HB is present in the anterior end

nanos (lf) results in HB being expressed in both axis: development of larvae lacking abdominal segments

Question 21

Bicoid transcription factor activates zygotic HB expression

Answer 21

Encodes a transcription factor that binds to DNA binding sites of the hunchback protein

Question 22

Dual regulation

Answer 22

Bicoid increases HB expression in the anterior portion of the cell by activating zygotic expression.

Nanos surpresses the expression of hunchback form a messenger RNA deposited by the mother.

Question 23

Gap genes

Answer 23

first genes zygotically expressed

maternal affect gene determine the axis. They interact with gap genes that are expressed in broad domains of the cell

they determine other large developmental domains of the body plan, they tell the cells to become a specific segment

Question 24

Gap genes (mutation)

Answer 24

Lf mutations in gap genes results in deletion of segments In gap lf mutants, contiguous set of segments

Question 25

Gap genes....

Answer 25

Encode transcription factors defining broad regions of the body plan, this expression pattern defines large domains along the anterior-posterior axis. Gap TFs regulates the expression of other gap genes and the expression of pair rule genes

Question 26

Kruppel and Knirps

Answer 26

Knirps regulates expression of Kruppel

Question 26

Kruppel and Knirps

Answer 26

Knirps regulates expression of Kruppel

Question 27

Pair-rule genes

Answer 27

``` segment the body plan expressed from the zygotic genome encode transcription factors pair-rule proteins define the segments of the body plan very specific pattern of expression ```

Question 28

Pair rule gene (lf)

Answer 28

portion of every other segment is missing. alternative deletion of segments. the segments deleted are the segments the pair-rule gene is expressed regulate pair rule genes and segment polarity genes

Question 29

Segment Polarity genes

Answer 29

pattern the segments expressed from the zygotic genome expressed in every segment segment polarity proteins pattern the structure of every segment

Question 30

segment polarity genes (lf)

Answer 30

every segment is present and every segment is defective. anterioir posterior polarity within a segmnet is often affected parts of the segment are deleted and duplicated

Question 31

Why do the segments look different from one another

Answer 31

homeosis: the transformation of one body part into the likeness of another homeotic selector gene

Question 32

Antennapedia

Answer 32

a switch for antenna versus leg development WT: antennapedia is expressed in leg primordia Antp(lf): no antennapedia resulting in legs becoming antenna Antp(gf): antenna results in antenna becoming legs This tells us that the atennapedia gene encodes a factor important for leg development but is not important to tell other cells to become a leg.

Question 33

Proboscipedia

Answer 33

homeotic selector genes are switch genes, Pb lf results in the transformation of the feeding tube into a pair of tarci, no proboscic and no supression of development of tarsus

Question 34

The origin of animals and relationship between animal groups

Answer 34

look for evidence in the fossil record porifera: sponges sponge genome is the second closest to the most recent common ancestor spongest are the base group of animals

Question 35

Hypothesis

Answer 35

what the most recent common ancestor looked like and what machinery did this ancient animal have that allowed the diversification into all these animal gorups

Question 36

Animal phylogeny

Answer 36

Placozoa (two layers of cells) difficult to group organism based on morphology bilaterians: symmetric; head and tail; axis of symmetry more related to starfish

Question 37

Common ancestor of bilaterians

Answer 37

Urbilateria had all the genetic machinery we consider in terms of the body plan; axis and organs

Question 38

a complex organism existed at the proteosome deutorostome split

Answer 38

complex machinery of developmental pathways back 650,000,000 years ago. it had the complex machinery to set up a central nerovus system, segmentation, regionlized gut, primitive heart and eyes, as well as body out growths

Question 39

Experimental/Observational approach of evo/devo

Answer 39

conservation of structure: similar amino acid sequence conservation of expression: genes of different organisms expressed similarly conservation of requirement: are the different genes required for similar things conservation of function (functional equivalence): can i take one gene in one organism and replace it in another and have that work

Question 40

Conservation of sequence (eyeless and pax6)

Answer 40

eyeless proteins in drosophila are very similar in sequence to the Pax6 protein in vertebrates

Question 41

Conservation of expression (eyeless and Pax6)

Answer 41

expression of eyeless and pax6 occurs in group of cells that give rise to the eye

Question 42

phyogenetic comparison of expression

Answer 42

expressed in the tissues that give rise to an array of photoreceptors

Question 43

Conservation of requirement

Answer 43

Eyeless is required for drosophila eye development 800 facet with photoreceptor compund eye is reduced in drosophila with no eyeless gene Pax6 is required for mouse eye development; homozygous knockout leads to no eye development

Question 44

Aniridia

Answer 44

Mutantions in human Pax6 result it aniridia; lack of an iris when heterozygous the functional allele shows haploinsufficiency resulting in a missing iris.

Question 45

Conservation of function (functional equivalence)

Answer 45

take the eyeless gene and place it in a vertebrate to see if there is the formation of the vertebrat eye; express eyeless gene in other parts of the body

Question 46

UAS GAL4 ectopic expression system

Answer 46

Take a yeast transcription factor and placed it in drosophila, seperate gal4 expression from the uasgal4 which is this cis element upon which gal4 will bind to activate transcription of galactose gene. we get extopic expression only when when we bring them together

Question 47

Binary or two component system

Answer 47

Fly stock A: UAS line; GAL4 bindging sites UASGAL4 next to YFG Fly stock B: Driver line; enhancer and GAL4 gene that expresses the GAL4 activation/DNA binding domain proteins mate the flies togehter in cells of the progeny where both genes are expressed you get ectopic expression of your gene

Question 48

Why a 2 component system

Answer 48

The ectopic expression of the gene may be lethal so are able to establish the UAS stock first with no expression Expression occurs only after we have crossed the UAS line with GAL4 driver line

Question 49

Ectopic expression of eyeless

Answer 49

Induces ectopic eye formation expression of eyeless in cells other than the eye wherever gal4 is expressed we see the formation of eye tissue

Question 50

Expressing Pax6

Answer 50

Create a UAS that contains the UAS dused to mouse Pax6 induction of ectopic eyes Pax6 from mice and eyeless can both induce ectopic eye formation in drosophila indicating the mouse pax6 is functionally equivalent to drosophila eyeless function

Question 51

Urbiletaria

Answer 51

experiments conclude that urbilaterian had a complicated set of geentic pathways that controlled the development of the primitive eye, heart structures, cns, segmentation, body wall out growth, body plan and throughoutput cut this common ancestor radiated through divergence to create all of the biletarian organism