part 2 Flashcards
What does forward genetics start with??
Mutant phenotype. Assume inactivation of gene needed for a process with have specific and reproducible effects
What does reverse genetics start with?
identified gene with known sequence. Interferer with function to introduce mutation e.g. via crispr cas 9
What is Brachyury ?
Mutatuon effecting length of mice tail length. it is semi dominant so if heterozygous an intermediate phenotype is seen eg. medium length of tail but when homozygous very short
What does Antimorphic mean?
mutant produces a product that interferes with wild type
Amorphic?
complete loss of function e.g. deletion
Hypomorphic?
partial loss of function
What are alkylating agents?
mutagen that donate alkyl groups to amino or kept groups in nucleotides changing pair sequencing eg.
EMS and ENU
What does EMS do?
it is an adenine analog, changes TGG to TAG which is a stop codon therefore a nonsense mutation occurs
What do Kit and Steel mutations show?
aneamia, infertility and pigmentation changes e.g. in mice there is spotting
What are steel and kit? And what is there role?
Steel codes for a ligand and Kit codes for a membrane receptor
role: in the development of germ cells, melanoblasts (melanin in the skin ) and production of blood cell stem cells
What is epistasis:
order of gene action in a pathway by crossing animals heterozygous for both mutations so you may get one F2 mutant with homozygous for both. Have 1/16th of a chance to show the phenotype of both
What is recessive epistasis?
phenotype of one mutation masks the effect of the other
How do you work out which gene is epistatic to the other?
Epistatic gene is further downstream than the other. the epistatic one is the one whose phenotype is seen
What is the Hh gene?
in drosophila involved in segmentation. Hh is a secreterd signalling molecule that binds to patched a transmembrane receptor
What is the role of Patched?
to suppress activity of smoothened unless Hh is bound to it
What does Smoothened do?
Activates Ci transcription factors that activate the transcription f wingless unless no Hh as then patches surpasses it
If Hh is mutated what is the phenotype?
dentricles cover whole larva
If Ptch is mutated what is the phenotype?
loss of dentricle zones
which is epistatic Patch or Hh
pathc as it is downstream and if both mutated ptch phenotype seen
What is seen in dorsal mutants?
dorsalised as lack of ventral regions and mesodermal specification does not occur
What is seen in cactus mutants?
centralised as lacks dorsal regions
How does dorsal protein enter the nucleus
on the ventral side to create a concentration gradient
What is Spatzle ?
ligand that binds to toll receptor
What is dorsal?
A transcription factor that activates mesodermal genes twist and snail and represses dorsal side genes Dpp. It acts as a morphogen so different thresholds result in different response
In ventralised embryos of drosophila what is seen?
cactus is mutated, so dorsal enters the nuclei and effects all of embryo as twist and snail activated and no dpp so all ventral cells
In dorsalised embryos what is seen?
dorsal, toll or spatzle mutated, so dorsal does not enter the nucleus and twist and snail not activate but dpp is active so all cells express dorsal fate
What are somites?
mesodermal tissue in segments along neural tube in embryo
What are rhombomere?
divided segment of neural tube in hindbrain
What are Hox genes?
a family of homeobox containing genes that are involvved in patterning the AP axis
Homeobox?
short region of DNA that encodes for a DNA binding domain called the homeodomain. genes contain gin this are known as box genes. highly conserved throughout evolution. 180 nucleotides long motif
What is a homeotic transformation?
A structure of the body plan is replaced by another
What does a mutation of the Ubx gene do?
result in the structure of the T3 segment in the fly to become T2 structures: halter replaced by another set of wings. it is a recessive mutation but does not effect amount of segments. Also the structure still respond to positional information but interpretation different as different structure.
What genes is the Bithorax complex made up of?
Abd - A, Abd-B and Ubx each gene has a homeobox of 180 nucleotides. They code for DNA biding proteins that control transcription
What is the Antennapedia complex?
also code for homeobox genes but controls anterior structure e.g. head and thorax
What does Antennapedia do? and what if it is mutated so dominant mutation?
controls for T2 segment and structure
Leg instead of antenna
Phenotype of Hoxb5 knockout in mouse?
limb correctly form yet more anterior position
What is FGF and its relevance to limb formation?
fibroblast growth factors. Signalling is required for limb bud formation
Knockout of Fgf10 or FgfR genes?
Embryo lacks limb bud
Apply Fgf4 to latex bead and insert?
limb bud forms
What is the Apical ectodermal ridge and its role in limb formation?
Rigid epithelial layer around the outer side of bud. Maintains the progressions zone. if removed growth stops at that state.
What is the progression zone and its role in limb formation?
mesenchyme tissue, rapidly diving and undifferentiated, the length of time it has been in PZ determines its cells fate along the pd axis. Eg if you remove young bud and put on old stump = normal limb forms but if you put old bud on young stump, only digits form
Some of polarising activity role?
mesenchyme tissue expressing Shh gene. if you transplant it to the anterior side of bud, forms mirror image digits too. It creates a concentration gradient that different thresholds cause formation of different digit etc . If you soak a bean in Shh and implant same result as mimic ZPA.
Deletion of Hoxa and Hoxd result?
absence of Shh expression so no digits so possibly they specify Shh
HoxD13 Mutation in humans results in?
synpolydactly = extra digits and fusing of digits
