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Genetics Exam 2
Vocab for Exam 2
| Term | Definition |
|---|---|
| Ascospore | A spore contained in an ascus or produced inside an ascus, typically found in fungi. |
| Auxotrophs | Mutant strains of bacteria that require additional nutritional supplements (e.g., amino acids, vitamins) for growth because they cannot synthesize a particular compound due to a genetic mutation. |
| Backcross | A cross between a hybrid organism and one of its parents or an individual genetically similar to its parent, often used to analyze inheritance patterns or recover parental genotypes. |
| Cis | Refers to two or more genetic elements (such as mutations or genes) located on the same DNA molecule or chromosome. |
| Competent Cells | Bacterial cells that are capable of taking up foreign DNA from their environment through the process of transformation. |
| Conjugation | A process of genetic exchange in bacteria involving direct cell-to-cell contact, typically mediated by a pilus, resulting in the transfer of plasmid or chromosomal DNA. |
| Coupling | Another term for the cis configuration, where two mutations or genes are present on the same DNA molecule. |
| Episome | A genetic element, such as a plasmid, that can exist either independently in the cytoplasm or integrated into the bacterial chromosome |
| F-factor (Fertility Factor) | A plasmid that enables bacteria to form a pilus and transfer genetic material during conjugation. Cells containing the F-factor are termed F+, while those lacking it are F-. |
| Hfr (High Frequency of Recombination) | A bacterial cell in which the F-factor has integrated into the chromosome, allowing for high-frequency transfer of chromosomal genes during conjugation. |
| IS2, IS3 (Insertion Sequences) | Short DNA sequences that can move within the genome, acting as simple transposable elements. They play a role in genetic rearrangements and the integration of episomes. |
| Linkage | The tendency of genes or genetic markers that are close together on a chromosome to be inherited together during meiosis or bacterial recombination. |
| Linkage Disequilibrium | The non-random association of alleles at different loci, often due to physical proximity or selection. |
| Linked | Describes genes or markers that are inherited together more frequently than would be expected by chance due to their physical proximity on a chromosome. |
| Locus/Loci | The specific physical location of a gene or genetic marker on a chromosome . |
| Minimal Media and Primary Components | A growth medium containing only the essential nutrients required by prototrophic bacteria (e.g., a carbon source, salts, and water). Auxotrophs cannot grow on minimal media without supplementation. |
| Nonrecombinant | Refers to cells or DNA molecules that retain the original combination of alleles or genetic markers, as opposed to recombinant types that have new combinations due to genetic exchange. |
| oriT | The specific site on a plasmid or episome where DNA transfer is initiated during conjugation. |
| oriV | The site on a plasmid or chromosome where DNA replication begins. |
| Phase | In genetics, may refer to the arrangement (cis or trans) of alleles or mutations on homologous chromosomes or DNA molecules. |
| Pilin | The protein subunit that makes up the pilus, a structure used during bacterial conjugation for cell-to-cell contact. |
| Pilus | A hair-like appendage found on the surface of many bacteria, essential for the process of conjugation. |
| Plasmid | A small, circular, double-stranded DNA molecule found in bacteria that replicates independently of the chromosomal DNA and often carries genes beneficial for survival (e.g., antibiotic resistance). |
| Prototrophs | Bacterial strains that can synthesize all compounds needed for growth from minimal media; the opposite of auxotrophs. |
| Recombination Fraction | The proportion of recombinant offspring or cells produced in a genetic cross, used to estimate the distance between genes. |
| Repulsion | The trans configuration, where two mutations or genes are located on different DNA molecules or homologous chromosomes. |
| Sonication | The use of high-frequency sound waves to disrupt cells or shear DNA into smaller fragments, often used in molecular biology protocols. |
| tra Genes | Genes located on the F-factor or related plasmids that encode proteins required for the formation of the pilus and the process of conjugation. |
| Trans | Refers to two genetic elements (such as mutations or genes) located on different DNA molecules or chromosomes. |
| Transduction | The process by which bacterial DNA is transferred from one bacterium to another by a bacteriophage (virus). |
| Transformation | The uptake and incorporation of free DNA from the environment into a bacterial cell, leading to genetic change. |
| Addition Rule | The addition rule applies to mutually exclusive events—events that cannot occur at the same time. Formula: P(A or B)=P(A)+P(B) |
| Multiplication Rule | The multiplication rule applies to independent events—events where the outcome of one does not affect the other. Formula: P(A or B)=P(A)*P(B) |
| Allele Frequency Calculations | Allele frequency is the proportion of a specific allele among all alleles for a gene in a population. Formula: Allele frequency = (Number of copies of the allele)/(Total number of all alleles for that gene) |
| Trihybrid Cross | Involves three gene pairs, each segregating independently. The branching method helps organize all possible genotype combinations and their probabilities. |
| Goodness-of-Fit Test (Chi-Squared Test) | Formula: X^2 = (Sum of All){((O-E)^2)/E) Where O = observed value, E = expected value |
| Degrees of Freedom (df): | df = number of categories - 1 |
| Prokaryotes vs Eukaryotic Gene Regulation | Prokaryotes: Gene-dense genomes w/ operons. One promoter Single RNA polymerase Eukaryotes: Gene-sparse genomes No operons; each gene typically has its own promoter and regulatory elements. Multiple types of RNA polymerases |
| Transcriptional Activators | Proteins that bind to specific DNA sequences in the promoter region to increase transcription. Zinc ions assist activators in binding the major groove of DNA. |
| Transcriptional Activator Example | GAL4p binds to the promoter, recruiting transcriptional machinery. Other proteins (e.g., GAL80p and GAL3p) sense environmental signals (like galactose) to modulate activator function. |
| Enhancer Sequences | DNA elements that can be located far from the gene they regulate. Bound by activator proteins, which recruit transcription factors and RNA polymerase. Multiple enhancers = increase transcription rates. |
| Chromatin Remodeling | Native chromatin structure restricts access to DNA binding sites. Chromatin-remodeling structures (CRS) reposition nucleosomes, making DNA accessible. |
| Chromatin Remodeling Example | Transcriptional activator proteins (TAP) bind DNA and recruit general transcription factors (e.g., TFIID, TBP) to the TATA box. RNA polymerase holoenzyme joins the complex to initiate transcription. |
| Transcriptional Silencers | DNA sequences that recruit protein complexes to repress gene expression. |
| Transcriptional Silencers Example | Drosophila Polycomb group proteins cause histone compaction, blocking transcription. |
| Epigenetic Regulation | The process by which cells control gene activity (turning genes "on" or "off") without altering the underlying DNA sequence. |
| Methylation | Methylation of cytosine residues in CpG islands can remodel chromatin and reduce transcription. Heavily methylated genes are typically silenced. |
| Imprinting | Certain genes are methylated during gametogenesis, leading to parent-of-origin-specific expression. Once established, imprinting marks are maintained through embryogenesis but are erased and reestablished in the germ line. |
| Alternative Splicing | Internal exons can be spliced in different combinations to produce multiple protein isoforms from a single gene. Terminal exons cannot be spliced out. |
| Deadenylation-dependent decay | Once the poly-A tail is reduced to 25-60 nucleotides, mRNA is decapped and degraded by exonucleases. |
| Deadenylation-independent decay | mRNA is decapped by enzymes or cleaved by endonucleases, then degraded by exonucleases. |
| RNA Interference (RNAi) | Dicer enzyme cleaves double-stranded RNA into ~25 nucleotide fragments. Fragments are loaded into the RNA-induced silencing complex (RISC). If the guide strand doesn't match the target mRNA perfectly, RISC blocks translation without cleavage. |
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