Lecture 20 Development

Question 1

Model organism (3 features and why)

Answer 1

1. Large collections of mutants with developmental defects (easier to understand gene function)
2. Genes and pathways are reserved (easier to model human disease)
3. Genomes are sequenced (easier to identify genes with mutant phenotype)

Question 2

Genetic techniques used to study development
Reverse genetics
____ to ____
(further explanation)
Forward genetics
____ to ____
(further explanation)
mutagenesis: ____
Stem cell and cloning
stem cell can be used for 1____ 2____

Answer 2

Reverse genetics
Genotype to phenotype
Start with a known gene, mutate it and observe the phenotype

Forward genetics
Phenotype to genotype
Start with a phenotype, identify the genes causing it.

Mutagenesis: the process of exposing organisms to mutagens to induce mutations.
Screen large numbers of mutants for your phenotype of interest.

Stem cell and cloning
Embryonic stem cells can be used for cloning the whole organism, or for therapeutic purposes of growing a specific tissue.

Question 3

Drosophilia development
Which genes control segmentation?
Experiment: use (what) to screen for (what) and (what) affecting (what)
Maternal effect:
mutation causes:

zygotic:
mutation causes:

Classes zygotic gene affecting segmentation identified from the experiment:
Class 1: ____ e.g. (2)
Class 2: ____ e.g. (4)
Class 3: ____ e.g. (2)

How do segmentation genes control segmentation?____
Experiment: manipulate ____ bind to ____ of ____, ____ is visualized by ____.
Reporter gene:____
Summary of embryonic patterning
Gap segment is created by ____
e.g. ____
Pair rule stripes are created by ____
E.g. ____

What genes determine the identity of a segment?
hox gene
→

homeotic Mutants: ____

Answer 3

Which genes control the embryonic segmentation?
Experiment: Mutagenesis screens for maternal effect and zygotic lethal mutations affecting segmentation.

Maternal effect: genes in the mother’s genome controlling the expression of RNAs and proteins supplied by the mother to the embryo, essential for early stages embryonic segmentation.
→ Maternal effects mutations cause female F3 progenies sterile.

Zygotic: genes in the embryonic genome controlling the expression of RNA and proteins essential for later stages embryonic segmentation.
→ Zygotic mutations cause F3 progenies to die as embryos.

Classes of zygotic mutations affecting segmentation identified in the experiment

Gap genes: divide the embryo into large segments
E.g. Kruppel, knirps.

Pair-rule genes: refine this pattern into every other smaller segments (7 Pairs)
E.g. even skipped, odd-skipped, paired, runt.

Segment polarity genes: further refine each smaller segments to smaller every other segments (14 pairs)
E.g. gooseberry, patched.

How do segmentation genes control embryonic expression?
Segmentation genes encode for transcription factors that control the expression of genes encode for materials essential for embryonic segmentation or transcription factors for later stages of embryonic development.

Experiment:
Manipulating which proteins bind to which cis regulatory elements of which zygotic gene, gene expression is visualized by reporter genes.

Reporter gene = produces proteins that allows for easy visualization of expression of target gene promoter

Summary of embryonic patterning

Gap segments are created by maternally-effect proteins
E.g. Bicoid and hunchback gene
Maternally deposited mRNA bicoid is concentrated at the anterior end.
Bicoid activates the expression of zygotes’ hunchback gene.
→ hunchback protein only appears at the posterior end.

Bicoid represses the expression of zygotes’ caudal gene.
→ caudal protein only appears at the posterior end.

Pair-rule stripes are created by the combinations of maternal-effect and gap proteins
E.g. eve stripe 2, bicoid and giant, hunchback and kruppel.

Bicoid and hunchback activates eve stripe 2 protein expressions.
giant and kruppel represses eve stripe 2 protein expressions.

What genes determine the identity of a segment?
Hox genes
→Expressed in spatially restricted domains
The order of the hox genes on the chromosome corresponds with the order in which they are expressed

Homeotic mutants
An organism in which a mutation in a homeotic gene (hox gene) causes one body part to transform into another.