Week 4 Flashcards
Define: hierarchical gene expression
Genes expressed at each stage in the process control the expression of genes that act later.
Define: cellular blastoderm
In Drosophila development, the structure formed by the nuclei in the single-cell embryo when they migrate to the periphery of the embryo and each nucleus becomes enclosed in its own cell membrane.
Define: gastrulation
A highly coordinated set of cell movements in which the cells of the blastoderm migrate inward, creating germ layers of cells within the embryo.
Define: segmentation
The formation of discrete parts or segments in the insect embryo.
What are the three germ layers formed by gastrulation in humans and most other animals?
- ectoderm
- mesoderm
- endoderm
Define: oocyte
The unfertilized egg cell produced by the mother.
- matures under control of the mother’s genes
Define: maternal-effect genes
Genes that are expressed by the mother but affect the phenotype of the offspring.
NOTE: bicoid + nanos are maternal effect genes!
What does it mean when we say the egg is a highly polarized cell?
One end of the egg is distinctly different from the other.
Does the bicoid affect the anterior or posterior of the Drosophila?
Anterior
- mothers that are mutant for bicoid have larvae that lack anterior structures
Does the nanos affect the anterior or posterior of the Drosophila?
Posterior
- mothers that are mutant for nanos have larvae that lack posterior structures
Why are the levels of hunchback and caudal proteins localized to the anterior and posterior ends of the Drosophila embryo?
They are localized to each end because bicoid and nanos control the translation of the hunchback and caudal mRNA.
- bicoid represses translation of caudal mRNA in the anterior
- nanos represses translation of hunchback mRNA in the posterior
- see figure 20.8
Would development happen normally if the mother has normal bicoid function, but the embryo does not? Why/why not?
Yes! Development would happen normally because bicoid is a maternal effect gene!!!
When does development start?
Development starts even BEFORE the zygote is formed, begins to occur in the oocyte.
Why can the genotype of the mother affect the phenotype of the developing embryo?
Because successful development of an embryo requires a functioning oocyte.
What gene(s) develop/set-up the anterior-posterior gradient?
Maternal Effect Genes
Which genes are the first to narrow down the anterior-posterior gradient?
Gap Genes
What do gap genes do?
Gap genes encode transcription factors that control genes in the next level of the regulatory hierarchy, which consists of pair-rule genes.
What is one example of a gap gene in Drosophila and what is its function?
Krüppel
- expressed in the middle region of the Drosophila embryo
- responsible for development of thoracic and abdominal segments
In order, what are the levels of genes that act on the development of the Drosophila?
- maternal-effect genes
- gap genes
- pair-rule genes
- segment-polarity genes
Would the pattern of segment-polarity gene expression be normal if one or more gap genes were not expressed properly? Why/why not?
No, since each level of gene acts to refine the one before it… if the gap genes were not expressed properly, we can predict that the segment-polarity gene expression would not be normal.
What is the role of homeotic (Hox) genes?
A homeotic gene is a gene that specifies the identity of a body part or segment during the embryonic development.
- expression of these genes are controlled by the segment-polarity genes and other genes expressed earlier on in the hierarchy
What is an example of homeotic gene in Drosophila and what is its responsibility?
Antennapedia
- responsible for specifying the development of the leg
Define: homeodomain
The DNA-binding domain in homeotic proteins, whose sequences are very similar from one homeotic protein to the next.
What are three key observations of homeotic genes that have been seen in almost all organisms studied?
- correlation among linear order along the chromosome
- anterior-posterior position in the embryo
- timing of expression
What are the differences/similarities between Drosophila and mammalian Hox genes?
Differences:
- in mammalians, do not specify limbs
Similarities:
- genes in each cluster are expressed according to their linear order along the chromosome
Why is it difficult to learn exactly what each function of Hox genes are in mammalians?
Because they have redundant/overlapping functions.
Define: loss-of-function mutation
A mutation that inactivates the normal function of a gene.
Define: gain-of-function mutation
Any mutation in which a gene is expressed in the wrong place or at the wrong time.
Define: downstream genes
A gene that functions later than another in development.
Define: cis-regulatory element
A short DNA sequence adjacent to a gene, usually at the 5’ end, that interacts with transcription factors.
Why does the mouse Pax6 gene induce the growth of eyes in Drosophila?
Master regulatory genes that control master development are often evolutionarily conserved, whereas the downstream genes can evolve new functions.
- downstream genes differ between the mouse and fruit fly but master regulatory gene (Pax6) remains the same - function of Pax6 is the same in all organisms (eye development)
What is the key information that fossils/fossil records provide us with?
- our only record of extinct species
- calibrate phylogenies in terms of time
- place evolutionary events in the context of Earth’s history
What are two factors that determine the likeliness of a historic species being a part of the fossil record?
- properties of organisms (i.e. do they have a skeleton?)
2. environment (more likely if from the sea - was burial likely?)
What are two ways that organisms without hard parts can develop a fossil record?
- trace fossils
2. molecular fossils
Define: trace fossils
A track of trail, such as a dinosaur track or the feeding trails of snails and trilobites, left by an animal as it moves about or burrows into sediments.
Define: molecular fossils
Sterols, bacterial lipids, and some pigment molecules, which are relatively resistant to decomposition, that accumulate in sedimentary rocks and document organisms that rarely form conventional fossils
Define: burgess shale
A sedimentary rock formation in BC that preserves a remarkable sampling of marine life during the initial diversification of animals.
Define: messel shale
A sedimentary rock formation in Germany, preserving fossils that document fish, birds, mammals, and reptiles from the beginning of the age of mammals.
Define: geologic timescale
The series of time divisions that mark Earth’s history.
How are we able to determine the age of archaeological samples?
Using radioactive dating - use various elements depending how old the fossil is.
- half-life
Why is it important for us to know the age of fossils?
To provide calibration points for phylogenies.
What is the effect of mass extinction on evolution?
Mass extinction essentially resents evolution.
- wipes out very large # of species
