lec 8- patterning the Drosophila embryo

Question 1

are all the axes in the Drosophila egg patterned?

Answer 1

yes

Question 2

what does the AP axis give rise to when it is divided into regions?

Answer 2

the head, thorax, abdomen, and terminal

Question 3

what are the 4 regions that the dorsal-ventral axis turns into?

Answer 3

-amniserosa (forms extraembryonic tissue)
-dorsal ectoderm (will form larval epidermis)
-ventral ectoderm (will form larval nervous system)
-mesoderm (will form muscles)

Question 4

what do maternal factors do?

Answer 4

responsible for the patterning of the info, lay down the positional info and set up the AP axis and the dorsal-ventrical axis

Question 5

what are maternal factors?

Answer 5

mRNA and proteins that are synthesized and deposited in the egg by the mother

Question 6

what does the maternal factor do after development occurs?

Answer 6

-the maternal mRNAs are translated and the resulting proteins activate the expression of genes from the embryos own DNA in a specific spatial pattern along each axis

Question 7

what causes the expression of zygotic genes?

Answer 7

maternal factors

Question 8

what do zygotic genes do?

Answer 8

set the stage for the next round of spatial patterning

Question 9

what are the types of zygotic genes and what do they do?

Answer 9

-the gap, pair-rule, and segmentation genes effectively divide the embryo into smaller and more distinct segments
-selector genes determine segment indentity
-gap genes divide embryo into hunchback (hb)
-pair-rule genes divide embryo into even skipped (eve) and fushi tarazu (ftz)
-segmentation genes divide the embryo into wingless (wg)

Question 10

what is the maternal effect?

Answer 10

when the mothers genotype determines what the offsprings phenotype will be

Question 11

if the mother is heterozygous for a mutant and the father is full mutant what will the phenotype results be?
(+/m x m/m = 50% +/m + m/m)

Answer 11

even though some are mutant, due to the mother having a wildtype allele, the children will all have normal phenotype

Question 12

if the mother is fully mutant but the father is heterozygous, will the offspring’s all have a normal phenotype?
(m/m x +/m = 100% +/m)

Answer 12

no, they will all have mutant phenotype because the wild type allele does not come from the mother who controls the phenotype of the offspring)

Question 13

what are the 3 types of mutations in maternal factors and what do they do?

Answer 13

-bicoid mutant: causes missing anterior structures
-torso mutant: causes both terminal regions to be missing
-nanos mutant: posterior is missing segments

Question 14

which maternally provided mRNAs set up the anterior-posterior axis and where are they located?

Answer 14

-bicoid mRNA is tightly attached to the anterior position, nanos mRNA is tightly attached to the posterior position
-both of these are tightly attached but the proteins are not. After translation both of them diffuse away from the poles and form gradients of each protein along the anterior-posterior axis
-hunchback and caudal mRNA is evenly distributed

Question 15

what is the bicoid maternal factors also considered?

Answer 15

a morphogen because it creates a gradient and sends a response

Question 16

what is correlation?

Answer 16

when a factor is present during a role in the right place and time, but isn’t proven to have had an effect on the role

Question 17

how do scientists know if a factor is necessary?

Answer 17

-by take away experiments, if being taken away stops the process, it is necessary
-if it being taken away does not stop the process, it is not necessary but it may still have a role due to redundancy

Question 18

how do scientists know a factor is sufficient?

Answer 18

if it can perform the role by itself with no intervention from anything else, if it causes the effect in a place or time where it usually doesn’t occur

Question 19

what are 3 forms of evidence to why bicoid is needed to pattern anterior structures?

Answer 19

1. when the anterior side of embryo is being formed, bicoid is present, meaning it is correlated
2. when an embryo lacks bicoid, it cannot form the anterior structures, indicating it is necessary for the formation
3. when bicoid was added to a bicoid mutant, it cause the formation of anterior structures, making it sufficient

Question 20

what is one type of posterior gene?

Answer 20

nanos

Question 21

what happens if an egg is mutated in posterior genes?

Answer 21

it results in the larvae being short due to lack of abdomen

Question 22

what acts as a repressor to stop hunchback mRNA from entering the posterior side of the embryo during fertilization?

Answer 22

nanos protein, it is crucial to stop the hunchback to have correct patterning

Question 23

what acts as a repressor to stop caudal mRNA from entering the anterior side of the embryo during fertilization?

Answer 23

bicoid protein, high concentration near anterior low at posterior, vice versa for caudal

Question 24

what types of proteins activate the anterior and posterior gap genes?

Answer 24

-bicoid proteins for anterior
-nanos and caudal proteins for posterior

Question 25

what does the torso mRNA turn into after fertilization?

Answer 25

it is translated into torso proteins

Question 26

what are torso proteins and where are they located?

Answer 26

they are receptors that are evenly distributed around the embryo

Question 27

where are the ligands (a fragment of the protein Trunk) that attach to the torso receptors located?

Answer 27

only at the poles and once activated, zygotic genes are expressed

Question 28

where is Trunk protein located and where is the protein that makes the ligands fragments located?

Answer 28

Trunk protein is present throughout the perivitelline space but the proteins that make the ligands are only found at the poles, very little ligand is produced, most of them bind to the torso receptors