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Definition
excellent genetics, easy to carry out large scale screens for mutants, easy to clone genes indentified by mutations
Advantages: sophisticated tools, easily scored patterning phenotypes, map-based gene cloning methods
Polytene chromosomes make isolation of genes possible |
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| Drosophila Fertilization: |
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Definition
•sperm enters egg that is already activated
• egg has already began specifying axes by the time sperm enters
• Micropyle: only site (future dorsal anterior region) where the sperm can enter the egg
• Competition between sperm and sperm can be much longer than a fly to block other sperm |
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| single layer of nuclei on the outside of the embryo |
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| small group of nuclei in the posterior that become enclosed in membranes (germline precursors) |
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| 6000 nuclei that become enclosed in membranes between divisions 13-14, no longer syncytial, also the time of mid-blastula transition: slow down of nuclear division and increase in RNA transcription |
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| when nuclei become surrounded by microtubules and microfilaments following division 10 |
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| Information for Embyronic Development |
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| comes from: transcription of embryonic/zygotic genome during embryogenesis or from transcription of the maternal genome during oogenesis |
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Definition
organism contains mixture of genotypically wildtype and mutant cells
When to Use: when tissue expression is unknown, when the protein functions many times in development, when the mutant is lethal
What it can Tell you: in which tissue the gene is active, at what time the gene is active, roles for otherwise hidden genes
How to Make one: mitotic recombination |
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Definition
| when the mesoderm folds inward during gastrulation |
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| Anterior and Posterior Midgut invaginations |
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| collection of cells along the ventral midline that form the trunk of the embryo |
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| Triple Mutant: bcd, nos, tor --> |
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| Nusslein-Volhard and Wischaus Conclusions: |
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Definition
Most mutations independently affect either the A/P or D/V axis
Maternal information specifies large regions of the body along the axes
Each large region is controlled by groups of genes that act together to produce and localize a morphagen
Zygotic genes specify smaller regions along the axis and are activated by maternal genes or interactions among themselves |
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Definition
| generated by terminal group genes in anterior unsegmented extremities, |
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Definition
terminal group in posterior
Mutations in these groups lead to losses of contiguous components of the larval patern
These groups provide all the information for A/P patterning |
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Definition
gene of the anterior group encodes a cytoplasmic determininant
Determined using bcd mRNA injected into different embryos, A/P patterns always formed in graded distribution with head forming at the point closest to the injection
Specifies fates in the anterior and represses posterior fates |
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Definition
anterior group genes that restrict the localization of bcd mRNA to the anterior
When not present the bcd gradient is not as steep and pattern elements are missing
Localization of bcd is mediated by 3’UTR untranslated region (necessary and sufficient)
Microtubule cytoskeleton plays key role in localizing bicoid mRNA |
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Definition
gap gene activated by bicoid
Contains bicoid binding sites in their promoters and reveals a concentration dependence for activation
Different affinities so activated genes will be activated at different concentrations |
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Definition
| gap gene repressed by bicoid |
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| Anterior Group Cell Fate Determiniation: |
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Definition
Activates transcription of a set of at least four embryonic gap genes
Represses the translation of caudal in the anteriror
Bicoid is the morphogen
Two other genes localize bicoid properly |
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gene known to be the central component of the posterior maternal system
Graded morphogen, mRNA is localized to posterior pole
Represses translation of maternally transcribed hunchback in the posterior preventing its interference in the normal patterning of the posterior |
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Definition
| maternal hunchback mRNA is present throughout the embryo but protein is only present in the anterior, maternal hunchback is not essential for normal development of embryos, in a nanos mutant hunchback protein is present in posterior and anterior, nanos expression is not essential for embryos lacking hunchback |
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Definition
| uniformly distributed in the embryo, required for nanos to repress translation of maternal hunchback |
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| Terminal Group of Maternal Genes |
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Definition
| receives positional information from somatic tissue, follicle cells of the ovary, contact developing egg at the poles to regulate the production of a ligand |
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Term
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Definition
protein present uniformly on the plasma membrane of the early embryo, receptor tyrosine kinase
Must be activated at poles of the embryo
Acts as a receptor for a signal from follicle cells at the poles and specifies terminal region by repressing a transcriptional inhibitor
Inhibits a transcriptional repressor of tailless and huckebein |
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Definition
protein secreted by follicle cells at the anterior and posterior poles that activates Torso protein
Not the ligand for torso, secreted into perivitelline space only at the poles
Cleave pro-peptide Trunk |
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Definition
Torso ligand, made by the embryo, not localized, cleaved by Torso-like to make it active
Secreted into perivitelline space, can rescue torso-like mutants but not torso mutants |
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| Maternal System Formations of A/P Patterns: |
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Definition
Anterior: graded morphogens acting as transcriptional activator and repressor
Posterior: localized translational repressor
Terminal: localized signaling from follicle cells at poles |
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Definition
embryonically expressed genes that specify the numbers, size and polarity of the segments
Mutants lacking gap genes have contiguous pattern deletions |
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| experiments where distribution of the products of one gene is examined in mutants for another potentially related genes |
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activated by gap genes, expression is a combined result of gap gene activation and interactions with other Pair Rule genes and also modular distribution of enhancer elements
Each pair is eventually expressed in seven stripes, overlapping
All genes encode transcription factors
Difference between primary and secondary determined through epistasis |
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Definition
mutations in these rules effects both primary and secondary pair genes
Most well known pair is even-skipped set of positive and negative regulatory interactions by both maternal and gap genes that activate the gene in different parts of the embryo
Modular nature of control scheme: each stripe is controlled by a unique combination of transcription factors
The same gap gene can act positively in one stripe and negatively in another |
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| Secondary pair rule Genes |
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Definition
| mutations do not have any effect on primary rule genes |
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Definition
: 14 stripes dependent on combinatorial activation by pair rule genes
Input of 7 odd parasegments plus 7 even parasegments
Specify segment boundaries and control segment polarity involving formation of graded distributions of wingless and hedgehog proteins or a signal cascade
Permanent signals that maintain segmental patterning infor via auto-regulatory feedback |
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| Segment Polarity Gene Activities |
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Definition
| Transcription factors, signal transduction components (Wnt), (Hh) |
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| Segment Polarity Gene Differences: |
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Definition
Function within cells rather than with syncytium therefore influence patterns through signaling instead of autonomous cellularly
Gap and pair rule gene expression is transient, segment polarity gene expression is maintained through development
Continued expression relies on cross-regulation through cell to cell interaction
Includes feedback loop of hedgehog and wingless signaling pathways |
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