Final Exam

Question 1

Mutant screen

Answer 1

a process where researchers examine a large number of mutagenized organisms and identify rare individuals with a mutant phenotype of interest

Question 2

What is the last photoreceptor cell to be assembled into the ommatidia of the Drosophila eyes?

Answer 2

R7 photoreceptor cell

Question 3

What is the function of R7 photoreceptor cells?

Answer 3

Contains rhodopsin proteins that enable flies to detect UV light

Question 4

Why do you separate mutations into groups?

Answer 4

You want to determine the number of different mutant genes represented in a collection which is achieved by sorting the mutations into complementation groups, each containing different mutant alleles of the same gene

Question 5

What are two methods in which scientists verify gene assignment to prevent wrong gene identification?

Answer 5

1) Add back a transgenic copy of the wild-type presumptive gene to the mutant organisms, to see if a wild-type phenotype results
2) TALENs–> mutagenize the candidate gene in an otherwise wild-type organisms to establish whether the mutant phenotype is produced

Question 6

What is the function of the Sev gene?

Answer 6

A transmembrane receptor protein present on the surface of R7 precursor cells

Question 7

What is the function of the Boss gene?

Answer 7

transmembrane ligand present on the R8 surface

Question 8

What happens when R7 contacts R8; Boss binds Sev?

Answer 8

A signal transduction cascade is initiated within the R7 precursor cell resulting in expression of genes that determine R7 cell fate

Question 9

pleiotropic

Answer 9

genes that are required for more than one developmental pathway

Question 10

redundant genes

Answer 10

genes whose products serve the same function in a pathway

Question 11

How do scientists try to identify pleiotropic genes in a developmental pathway?

Answer 11

Modifier screen

Question 12

Mutations that cause the eyes of sev hypomorphs to appear more mutant

Answer 12

dominant enhancers (E-)

Question 13

Mutations that cause sev hypomorphic eyes to appear more like wild-type

Answer 13

Dominant suppressors (S-)

Question 14

In what conditions are you able to see the effects of mutant phenotypes?

Answer 14

In a sensitized background (in sev hypomorphs) does the mutation have an effect on eye morphology

Question 15

What genes play a part in establishing regional differences in the embryo that lead to the proper segment number?

Answer 15

maternal effect genes

Question 16

Zygotic segmentation genes

Answer 16

expressed by the zygote’s own genome, subdivides the body into an array of essentially identical body segments

Question 17

Homeotic genes

Answer 17

a set of genes that encode transcription factors, assigns a unique identity to each body segment

Question 18

maternal effect mutations

Answer 18

recessive mutations in maternal genes that influence embryonic development

Question 19

Bicoidn (bcd)

Answer 19

The protein product that is a transcription factor whose mRNA is localized at the anterior tip of the egg cytoplasm that is translated after fertilization. It diffuses from the anterior end to produce a high-to-low, anterior-to-posterior concentration gradient that determines most aspects of the head and thorax development.

Question 20

morphagen

Answer 20

a substance that defines different cell fates in a concentration-dependent matter ex) bicoid is a morphagen

Question 21

What are the two ways in which bicoid works?

Answer 21

1) as a transcription factor that helps control the transcription of genes farther down the regulatory pathways
2) a translational repressor (targets transcript of the caudal (cad) gene)

Question 22

Caudal (cad) gene

Answer 22

• higher conc. of the Cad protein at the posterior end of the embryo and lower concentrations toward the anterior
• plays an important role in activating genes expressed later in the segmentation pathway to generate posterior structures

Question 23

Nanos (nos) genes

Answer 23

The nanos mRNA is localized to the posterior egg cytoplasm by proteins encoded by other maternal genes. It is translated during the early nuclear division stages. However, Nos protein functions only as a translational repressor. Targets maternally supplied transcript of the hunchback (hb) gene which is deposited in the egg during oogenesis and is distributed uniformly before fertilization.

Question 24

what are the three classes of zygotic segmentation genes?

Answer 24

1) gap genes
2) pair-rule
3) segment polarity gene

Question 25

The first zygotic genes to be transcribed

Answer 25

gap genes

Question 26

how do maternal transcription factor gradients ensure that the various gap genes are expressed in their broad zone at the proper position in the embryo?

Answer 26

Binding sites in the enhancers of the gap genes have different affinities for the maternal transcription factors

Question 27

Pair-rule genes

Answer 27

Encode transcription factors that are expressed in seven stripes in preblastoderm and blastoderm embryos. They generate more sharply defined sections.

Question 28

Functions to determine certain patterns that are repeated in each segment

Answer 28

Segment polarity genes

Question 29

What directly regulates certain segment polarity genes?

Answer 29

the transcription factors encoded by pair-rule genes initiate the pattern by directly regulating certain segment polarity genes and is maintained by interaction between various cell genes

Question 30

What are two of the segment polarity genes? What are they responsible for?

Answer 30

hedgehog (hh) and wingless (wg)

These proteins together with transcription factors are responsible for many aspects of segment patterning

Question 31

What are signal transduction pathways?

Answer 31

They enable a signal received from a receptor on the cell’s surface to be converted to a final intracellular regulatory response

Question 32

What regulates homeotic genes?

Answer 32

They are regulated by the hap, pair-rule and segment polarity genes

Question 33

homeotic mutations

Answer 33

cause particular segments or parts of them, to develop as if they were located elsewhere in the body

Question 34

mutations affecting segments in the abdomen and posterior thorax

Answer 34

bithorax complex (BX-C)

Question 35

mutations affecting segments in the head and anterior thorax

Answer 35

antennapedia complex (ANT-C)

Question 36

What are infra-abdominal (iab) mutations?

Answer 36

They are mutations affecting abdominal segments

Question 37

What is a homeobox?

Answer 37

region of sequence homology

Question 38

hox genes

Answer 38

clustered homeobox genes