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| Understanding complex genetic pathways begins with three steps which are |
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Definition
1. Obtain many single gene mutations - test for dominance and recessiveness by a cross to wild type.
2. Test the mutants for allelism - determine if the mutations occur in the same gene or in different genes by a complementation test
3. Combine mutants in pairs to form double mutants - test for gene interaction |
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| Gene interactions is inferred from |
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| the phenotype of the double mutants |
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| When genes act in the same pathway, they |
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Definition
| modify the dihybrid ratios |
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| To test for genetic interaction, we first |
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Definition
| obtain F1 progeny by crossing the pairs of mutant strains |
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| F2 progeny will give 9:3:3:1 ratio when |
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Definition
| two genes do not interact |
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| Duplicate functions happen when |
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Definition
| A and B do the same thing. Either A or B is needed but not both. |
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| In duplicate functions, the mutant phenotype is observed only with the |
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Definition
| double recessive homozygote |
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| a form of gene interaction whereby one gene (A) interferes with the phenotypic expression of another nonallelic gene (B) |
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Definition
| epistasis of recessive genes |
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| epistasis of dominant alleles |
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| allele that reverses the effect of a mutation of another gene, resulting in the normal wild type phenotype |
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| How is suppression different from epistasis? |
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Definition
The suppressor cancels the expression of a mutant allele and restores it to the wild type.
In F2 dihybrids, sometimes you get only two phenotypes segregating (as opposed to three in epistasis). |
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Term
| What is another way that suppression is different from epistasis? |
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Definition
| A suppressor mutation brings the wild type function of A back, unlike epistasis, where the epistatic gene simply masks the expression of another gene. Although the ratios are similar to what is seen in epistasis, the phenotypic classes are completely different. |
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| process of identifying new genes that contribute to a known function |
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| where the gene is known and mutants are analyzed to reveal the function |
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| a mutant whose viability is dependent on a set of (permissive) conditions. An example is auxotrophs and temperature-sensitive |
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Definition
| a mutant whose viability is dependent on a set of (permissive) conditions. An example is auxotrophs and temperature-sensitive |
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Term
| Conditional genetic screens have the advantage of |
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Definition
| revealing essential genes, in which a null mutation would be lethal |
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Term
| Cell division cylce (Cdc) mutants can be identified based on the |
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Definition
| cellular structure of budding yeast |
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Term
| Some features of the S. cerevisiae cell cycle that differ from multicellular organisms are: |
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Definition
1. No normal G2 phase. Instead, the spindle begins to form in the nucleus during S phase.
2. The cell divides by budding.
3. The nuclear envelope stays intact during mitosis. |
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