Final Exam Flashcards
(38 cards)
Mutant screen
a process where researchers examine a large number of mutagenized organisms and identify rare individuals with a mutant phenotype of interest
What is the last photoreceptor cell to be assembled into the ommatidia of the Drosophila eyes?
R7 photoreceptor cell
What is the function of R7 photoreceptor cells?
Contains rhodopsin proteins that enable flies to detect UV light
Why do you separate mutations into groups?
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
What are two methods in which scientists verify gene assignment to prevent wrong gene identification?
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
What is the function of the Sev gene?
A transmembrane receptor protein present on the surface of R7 precursor cells
What is the function of the Boss gene?
transmembrane ligand present on the R8 surface
What happens when R7 contacts R8; Boss binds Sev?
A signal transduction cascade is initiated within the R7 precursor cell resulting in expression of genes that determine R7 cell fate
pleiotropic
genes that are required for more than one developmental pathway
redundant genes
genes whose products serve the same function in a pathway
How do scientists try to identify pleiotropic genes in a developmental pathway?
Modifier screen
Mutations that cause the eyes of sev hypomorphs to appear more mutant
dominant enhancers (E-)
Mutations that cause sev hypomorphic eyes to appear more like wild-type
Dominant suppressors (S-)
In what conditions are you able to see the effects of mutant phenotypes?
In a sensitized background (in sev hypomorphs) does the mutation have an effect on eye morphology
What genes play a part in establishing regional differences in the embryo that lead to the proper segment number?
maternal effect genes
Zygotic segmentation genes
expressed by the zygote’s own genome, subdivides the body into an array of essentially identical body segments
Homeotic genes
a set of genes that encode transcription factors, assigns a unique identity to each body segment
maternal effect mutations
recessive mutations in maternal genes that influence embryonic development
Bicoidn (bcd)
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.
morphagen
a substance that defines different cell fates in a concentration-dependent matter ex) bicoid is a morphagen
What are the two ways in which bicoid works?
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)
Caudal (cad) gene
- 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
Nanos (nos) genes
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.
what are the three classes of zygotic segmentation genes?
1) gap genes
2) pair-rule
3) segment polarity gene
