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Fund Genetics
Unit 2
| Term | Definition |
|---|---|
| Deletion | A missing region in a chromosome |
| Terminal Deletion | Deletion at the end of chromosome |
| Intercalary Deletion | Deletion within the interior |
| Chromosome Aberrations | Change in structure or number of chromosome |
| Duplication | A repeated/double region of chromosome; caused by replication errors or unequal crossing |
| What does duplication result in | Gene redundancy and phenotypic variation |
| Inversion | Rearrangement of the linear gene sequence, requiring two breaks. Can lead to deletion and duplication |
| Paracentric Inversion | The centromere is not included ; Crossing over within the inversion loop can produce abnormal chromatids that form during ANAPHASE that leads to acentric and dicentric |
| Acentric Inversion | No centromere --> Fragments |
| Dicentric | dicentric (two centromeres) chromosomes → Bridges |
| Pericentric Inversion | The ONE centromere is included. |
| Translocation | A segment moves from one chromosome to a different chromosome in close proximity; produces unbalanced gametes that might be missing genetic material or have extra/duplicates |
| Nonreciprocal translocation | A piece from ONE chromosome moves. |
| Reciprocal translocation | Pieces are EXCHANGED between two chromosomes |
| Robertsonian Translocations | acrocentric chromosomes (centromere near one end) |
| monohybrid | one gene, two diff. alleles; cross reveals how one trait is transmitted from generation to generation ; 3:1 |
| dihybrid | 9:3:3:1 |
| Gene | unit of inheritance that controls a specific trait |
| Allele | alternative forms of a single gene |
| Genotype | genetic makeup, or combination of alleles, in an individual |
| Phenotype | the physical manifestation of the genotype |
| Heterozygous | when the alleles are different |
| Dominant | results in a given phenotype when only one copy of the allele is present (Dd or DD) |
| Recessive | Two copies (dd) must be present to observe the phenotype. |
| Self-cross | A mating between organisms with the same genetic makeup |
| True-Breeding | Self-fertilizing organisms that result in 100% of the offspring having the parents' phenotype |
| Unit Factors in Pairs | Genetic traits are controlled by unit factors (genes) that exist in pairs (alleles) in individual organisms (DD, dd, Dd) |
| Law of Dominance | When an individual has two unlike alleles, one is dominant (expressed) and the other is recessive (masked). (Dd) |
| Law of Segregation (Monohybrid) | During gamete formation, paired alleles segregate randomly, so each gamete receives one allele with equal likelihood (50/50 split). |
| Law of Independent Assortment (Dihybrid) | Alleles for different genes assort/seperate independently during gamete formation. |
| Punnett Squares | help visualize the genotypic outcomes of a cross. |
| A Testcross | (crossing an unknown dominant individual with a homozygous recessive individual) determines the unknown genotype. |
| Homozygous | when both alleles are the same |
| Product Law of Probabilities | product of their individual probabilities. |
| Sum Law of Probabilities | sum of the individual probabilities (the 4 end totals) |
| Autosomal Recessive Traits | Typically skip generations, and appear equally in males and females (e.g., Albinism). |
| Autosomal Dominant Traits | Typically appear in every generation, and all affected offspring usually have an affected parent (e.g., Huntington Disease). |
| Pedigrees | track inheritance patterns in families |
| Mutaion | an alteration in the DNA sequence ( MOLECULAR LEVEL) where protein may or may not be altered and/or functioning |
| What's a wild-type? | Normal, most frequent, usually dominant |
| Point Mutation (Base Substitution) | A change in one base pair to another. Purine for purine/pyrimidine for pyrimidine (transition-missense & silent) or purine for pyrimidine/vice versa (transversion-nonsense) |
| Missense | Codes for a different amino acid (Transition) |
| Nonsense | Triplet is changed to a stop codon (Transversion) |
| Silent | Codon is altered but still encodes the same amino acid (Transition) |
| Frameshift Mutation | Resulting from the addition or removal of nucleotides (insertions/deletions). |
| What's the types of molecular change in genetic mutations? | Point, insertion, deletion |
| What's the types of effect on function in genetic mutations? | Loss of func and Gain of func Recessive/dominant DN/CA Visible Lethal Conditional Neutral |
| What's the types of location of mutation in genetic mutations? | Coding vs. regulatory region, Somatic vs. germ cells, autosomal vs. sex-linked |
| What's the 3 major ways to classify genetic mutations? | Type of molecular change, Effect on function, and location of mutation |
| Loss-of-Function (LOF) | Reduces or eliminates the function of the gene product. A complete LOF is called "null". Most LOF mutations are recessive, but they can be dominant (haploinsufficiency). |
| Gain-of-Function (GOF) | Enhanced, new, or negative gene functions. Most are dominant. In gene regulatory regions. Types include |
| What are the types of GOF? | - those that create new activity, - those that are dominant negative (interfere with the wild-type product) - those that are constitutively active (always "on"). |
| What's Dominant negative in GOF? | interfere with the wild-type product |
| What's Constitutively active? | those that are constitutively active (always "on"). |
| Regulatory | affect the regulation of gene expression; Somatic & Germ cell |
| Somatic vs. Germ Cell (Cell Type) | Somatic mutations occur in non-germ cells and are not heritable. Germ = sperm → Heritable |
| Coding vs. Regulatory Region | Mutations in gene control regions or transcription factors are regulatory mutations and affect gene expression regulation. |
| Autosomal vs. Sex-linked (Chromosome Type) | Autosomal = automatically any chromosome BUT sex chromes X-linked or Y-linked = sex chromosome |
| What are the 2 different causes of mutation? | Spontaneous or Induced |
| Spontaneous | Occur randomly and accidentally; not associated with specific external agents. |
| What are the different spontaneous mutations? | Mispairing, Tautomeric shift, insertions/deletions, depurination, deamination, reactive oxidation, transposable elements |
| Mispairing | due to tautomeric shifts or random error |
| Tautomeric shifts | in nitrogenous bases can lead to permanent base-pair changes → point mutations (transitions) |
| insertions/deletions | B/c of replication slippage common in tandemly repeated sequences |
| Depurination | loss of a purine base (G)’ |
| Deamination | conversion of amino group in C or A to a keto group |
| Reactive Oxidation | a chemical that removes electrons by adding an oxygen groups (superoxides, hydroxyl radicals, H2O2 → mispairing |
| Transposable elements | transposons or "jumping genes"lots of them ; Move around the genome (50% human g) ; Ability to hop in and out of coding sequence or regulatory regions can cause mutations |
| Induced | Influenced by external factors (mutagens, UV radiation, chemicals, etc.) to get a specific change |
| Base analogs | substitute for nitrogenous bases |
| Alkylating agents | donate alkyl groups to nucleotides (eg. mustard gas) |
| intercalating agents | wedge between base pairs due to similar shape that mimics og (eg. Ethidium Bromide - fluorescent dye in biology) |
| Adduct-forming agents | covalently bind DNA (eg. Acetylaldehyde in cigarette smoke) |
| Radiation | High energy (X rays, gamma rays) ionize (gain a +/- charge) molecules and generate free radicals (molecule w/ unpaired electron). UV light creates pyrimidine dimers, often with thymines. |
| How do free radicals affect genetic material ? | 1) Altering nitrogenous bases 2) Breaking phosphodiester bonds 3) Disrupting chromosome integrity 4) Producing chromosomal deletions, translocations, and fragmentation |
| What are the single strand repairing mechanisms? | Proofreading, Mismatch repair, Base Excision Repair, Nucleotide Excision Repair |
| Proofreading | DNA polymerase uses its 3' to 5' exonuclease activity to remove incorrect nucleotides during replication. |
| Mismatch Repair (MMR) | Deals with errors remaining after proofreading. Recognizes "nicks" (single-stranded breaks that come from removal of RNA primers) in the new strand for discrimination. |
| Base Excision Repair (BER) | Fixes specific damaged bases (e.g., uracil from cytosine deamination). A glycosylase removes the base, leaving the backbone, which is then removed and replaced and sealed by ligase. |
| Nucleotide Excision Repair (NER) | Corrects bulky lesions (like UV-induced THYMINE DIMERS) that distort the double helix. |
| What are the double strand repairing mechanisms? | Homologous Recombination Repair and Non-Homologous End Joining |
| Homologous Recombination Repair (HRR) | Highly accurate system that uses information from the homologous chromosome or sister chromatid to repair the break. |
| Non-Homologous End Joining (NHEJ) | An error-prone repair system that glues (ligates) two broken ends together. |
| Incomplete (Partial) Dominance | |
| Codominance | |
| Multiple Alleles | More than two alleles exist for a single gene. Like Human Blood |
| Recessive Lethal Alleles | Result in the death of the individual when two copies are present. The allele may behave dominantly for a visible trait, but recessively for lethality. 2-1 ratio |
| Dominant Lethal Alleles | One copy leads to death, making them rare in populations (e.g., Huntington's Disease). |
| Equal Contributions | A single trait driven by two genes with equal contributions but without interaction, yielding the standard 9-3-3-1 ratio. |
| Complementary Gene Interaction | A wild-type allele for each gene is required to produce the trait. Phenotypic ratio of 9-7. |
| Epistatic Gene Interactions | The expression of one gene masks/modifies (epistatic) the expression of another gene (hypostatic - the gene that's masked). |
| The masking allele is homozygous recessive. The phenotypic ratio is 9-3-4. Eg. ee masks B. | |
| Dominant Epistasis I | One copy of the masking allele is sufficient to mask the other gene. The phenotypic ratio is 12-3-1. Example B masks A |
| Redundant Genes | Only one dominant allele for either gene is sufficient to produce the phenotype. This results in a phenotypic ratio of 15-1. |
| What is Sex-Linkage? | traits associated with genes located on the sex chromosomes. |
| X-linked Genes | Display phenotypes associated with sex |
| What are the X-linked RECESSIVE patterns? | Affected mothers pass trait to all sons Aff. fathers pass trait to all carrier daughters Carr. mothers pass trait on to half sons and all daughters Children of mother carrier and affected father have a 50% chance of having the trait |
| Y-Linked Genes | RARE ; allele must be dominant to display ; affected male passes to all sons |
| What is Phenotypic Variation? | Describes the degree to which a genotype is expressed |
| Pleiotropy | (The opposite of gene interaction) A single gene affects multiple distinct phenotypic traits. eg. Marfan syndrome, where a mutation in the fibrillin gene leads to effects in the lens, skeleton, and heart. |
| Penetrance | The percentage of individuals showing some degree of expression of a mutant genotype. If penetrance is less than 100%, it is incomplete penetrance |
| Expressivity | The range of expression of the mutant genotype. If the phenotype varies greatly, it is variable expressivity. |
| Polydactyly | exhibits incomplete penetrance and variable expressivity |
| What's the causes of Phenotypic Variation? | Genetic background/context, Temperature, Nutrition, Onset of Genetic Expression, and Genetic Anticipation |
| Genetic Background | Additional genes can modify the phenotype, known as the position effect. |
| Position effect | gene's expression is influenced by its physical location relative to other genetic material (e.g., location near heterochromatin(no expression) versus euchromatin(gene expression)). |
| Temperature | Conditional mutations, where the chemical activity depends on the kinetic energy which depends on temperature. |
| Nutrition | different phenotypes depending on available nutrients. eg. humans - Lactose intolerance |
| Onset of Genetic Expression | Genes are required at distinct times during an organism’s life span |
| Genetic Anticipation | The progressive earlier age of onset and increased severity of a trait with each successive generation |
| Extranuclear inheritance | genetic transmission through the cytoplasm, outside of the nucleus. This results in a non-Mendelian, uniparental/maternal inheritance pattern. |
| What are the types of Extranuclear (outside of nucleus) Inheritance? | Organelle Heredity, Infectious Heredity, and Maternal Effect |
| Organelle Heredity | from DNA in mitochondria and chloroplasts |
| Mitochondrial Inheritance | mtDNA is maternally inherited to all offspring - Maternal gamete contains MUCH more mitochondria (= simple dilution model) -paternal mitochon. are actively degraded, - Mutations in mtDNA --> defects in the nervous system and muscles. |
| Chloroplast Inheritance | The progeny inherit the phenotype of the $mt(+)$ mating type parent (uniparental inheritance). |
| Infectious Heredity | Transmission of traits from symbionts or parasitic microorganisms. |
| Maternal Effect | The offspring’s phenotype is determined by nuclear gene products stored in the egg cytoplasm by the mother prior to fertilization. The mother's genotype controls the initial phenotype. = Zygotic gene expression - OFF |
Created by:
jordinii