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Genetics
Exam 2: Lesson 4-7
| Term | Definition |
|---|---|
| Age of onset | The time of life at which symptoms of a genetic disease appear. |
| Codominance | A pattern of inheritance inwhich two alleles are both expressed in theheterozygouscondition. For example, aperson with the genotype IAIB has the bloodtype AB and expresses both surface antigensA and B. |
| complementation | the presence of 2 different mutant alleles in the same organism produces a wild-type phenotype. Usually happens because the two mutations are in different genes, so the organism carries one copy of each mutant allele and one copy of each wild-type allele. |
| Conditional Lethal Alleles | An allele that is lethal, but only under certain environmental conditions. |
| Dominant-negative mutations | A mutation that produces an altered gene product that acts antagonistically to the normal gene product. Shows a dominant pattern of inheritance. |
| Epistasis | An inheritance pattern in which one gene can mask the phenotypic effects of a different gene. |
| Essential gene | A gene that is essential for survival of the organism. |
| Expressivity | The degree to which a trait is expressed. For example, flowers with deep red color have a high expressivity of the allele for red flower color. |
| Gain-of-function mutations | A mutation that causes a gene to be expressed in an additional place where it is not normally expressed or during a stage of development when it is not normally expressed or at a level that is higher than normal. |
| gene interaction | The phenomenon in which two or more different genes influence the outcome of a single trait. |
| Gene redundancy | The phenomenon in which an inactive gene is compensated for by another gene with the same or a similar function. |
| Genetic polymorphism | (1) the prevalence of two or more phenotypic forms in a population; (2) the phenomenon in which a gene exists in two or more alleles within a population and each allele is found at a frequency of 1% or higher. |
| Haploinsufficiency | The phenomenon in which a person has only a single functional copy of a gene, which does not produce a normal phenotype. Shows a dominant pattern of inheritance. |
| Homodimer | A protein formed when two polypeptides encoded by the same gene bind to each other to form a dimer. |
| Incomplete Dominance | A pattern of inheritancein which a heterozygote that carriestwo different alleles exhibits a phenotypethat is intermediate to those of the correspondinghomozygous individuals. |
| Chloroplast DNA (cpDNA) | The genetic material found within a chloroplast. |
| Complex traits | Characteristics that are determined by several genes and are significantly influenced by environmental factors. |
| Continuous traits | Traits for which the phenotype exhibits a continuum. |
| Cytoplasmic inheritance | the inheritance of genetic material that is not found within the nucleus. |
| Discontinuous traits | A trait for which each offspring can be put into a particular phenotypic category. |
| DNA methylation | The phenomenon in which an enzyme covalently attaches a methyl group (—CH3) to a base (adenine or cytosine) in DNA. |
| Endosymbiosis | A symbiotic relationship in which the symbiont actually lives inside (endo) the host (the larger of the two species). |
| Endosymbiosis theory | The theory that the ancient origin of plastids and mitochondria was the result of certain species of bacteria taking up residence within primordial eukaryotic cells. |
| Epigenetic inheritance | A pattern in which a modification occurs to a nuclear gene or chromosome that alters gene expression, but is not permanent over the course of many generations. |
| Frequency distribution | A graph that shows the numbers of individuals that are found in each of several phenotypic categories. |
| Genomic imprinting | A pattern of inheritance that involves a change in a single gene or chromosome during gamete formation. Depending on whether the modification occurs during spermatogenesis or oogenesis |
| Heterogamous | Describes a species that produces two morphologically different types of gametes (i.e., sperm and eggs). |
| Heteroplasmy | The condition of a cell that contains variation in a particular type of organelle. For example, a plant cell could contain some chloroplasts that make chlorophyll and other chloroplasts that do not. |
| Imprinting control region (ICR) | A DNA region that is differentially methylated and plays a role in genomic imprinting. |
| Maternal effect | An inheritance pattern for certain nuclear genes in which the genotype of the mother directly determines the phenotypic traits of her offspring. |
| Maternal inheritance | Inheritance of DNA that occurs through the cytoplasm of the egg. |
| Monoallelic expression | The phenomenon in which only one of the two alleles of a given gene is transcriptionally expressed because the other allele has been silenced due to imprinting. |
| Mitochondrial DNA (mtDNA) | The DNA found within mitochondria. |
| Normal distribution | A distribution for a large sample in which the trait of interest varies in a symmetrical way around an average value. |
| Nuclear genes | Genes that are located on chromosomes found in the nucleus of eukaryotic cells. |
| Nucleoid | A darkly staining region that contains the genetic material of mitochondria, chloroplasts, or bacteria |
| Paternal leakage | The phenomenon in whichmaternal inheritance is generally observed,but the male parent may, on rare occasions,provide mitochondria or chloroplasts to thezygote. |
| Polygenic inheritance | Refers to traits that are governed by two or more different genes. |
| Quantitative genetics | The area of genetics concerned with traits that can be described in a quantitative way. |
| Quantitative trait locus (QTL) | The location on a chromosome where one or more genesthat influence quantitative traits reside. |
| Reciprocal cross | A pair of crosses in which the traits of the two parents differ with regard to sex. |
| antiparallel | The opposite orientation of the two strands of a DNA molecule with regard to their 3′ and 5′ ends. |
| B DNA | The predominant form of DNA in living cells. It is a right-handed DNA helix with 10 bp per turn. |
| Chargaff's rule (AT/GC rule) | The observation that in DNA, the amount of A equals that of T, and the amount of G equals that of C. |
| Complementary | DNA that ismade from an RNA template by the actionof reverse transcriptase. |
| DNase | An enzyme that cuts the sugar-phosphate backbone in DNA. |
| Major Groove | An enzyme that cuts the sugar-phosphate backbone in DNA. |
| Minor Groove | A narrow indentation in the DNA double helix in which the bases have access to water. |
| Molecular Genetics | The study of DNA structure and function at the molecular level. |
| Nucleoside | Structure in which a base is attached only to a sugar, with no phosphate attached to the sugar. |
| Protease | An enzyme that digests the polypeptide backbone in proteins. |
| Purines | A type of nitrogenous base that has a double-ring structure. Examples are adenine and guanine. |
| Pyrimidines | A type of nitrogenous base that has a single-ring structure. Examples are cytosine, thymine, and uracil. |
| RNase | An enzyme that cuts the sugar-phosphate backbone in RNA. |
| Transformation | (1) introduction of a plasmid vector or segment of chromosomal DNA into a bacterial cell; (2) conversion of a normal cell into a malignant cell. |
| Z DNA | A left-handed DNA double helix that is found occasionally in living cells. |
| Autonomous elements | A transposable element that contains all of the information necessary for transposition or retrotransposition to take place. |
| 30 nm fiber | The association of nucleosomes to form a more compact structure that is 30 nm in diameter. |
| Direct repeats (DRs) | Short DNA sequences that flank transposable elements and in which the DNA sequence is repeated in the same direction. |
| DNA gyrase | Also known as topoisomerase II; an enzyme that introduces negative supercoils into DNA using energy from ATP. Gyrase can also relax positive supercoils when they occur. |
| DNA supercoiling | The formation of additional coils in DNA due to twisting forces. |
| Euchromatin | DNA that is not highly compacted and may be transcriptionally active. |
| Exon shuffling | The phenomenon in which exons are transferred between different genes during evolution. |
| Heterochromatin | Regions of chromosomes that are always heterochromatic and are permanently transcriptionally inactive. |
| Highly repetitive sequences | DNA sequences that are found tens of thousands or even millions of times throughout a genome. |
| Histone proteins | A group of proteins involved in forming the nucleosome structure of eukaryotic chromatin. |
| Insertion element (IS element) | The simplest transposable element, which is commonly found in bacteria. |
| Integrase | An enzyme that functions in the integration of viral DNA or retrotransposons into a chromosome. |
| Intergenic regions | In a chromosome, a region of non-transcribed DNA that lies between two different genes. |
| Introns | Intervening sequences that are found between exons. Introns are spliced out of the RNA prior to translation. |
| Long terminal repeats (LTRs) | Base sequences containing many short segments that are tandemly repeated. They are found in retroviruses and LTR retrotransposons. |
| Inverted repeats (IRs) | DNA sequences found in transposable elements that are identical (or very similar) but run in opposite directions. |
| Loop domains | A segment of chromatin that is organized into a loop. |
| LTR retrotransposons | A type of retrotransposon that is evolutionarily related to a retrovirus and has long terminal repeats. |
| matrix-attachment regions (MARs) | DNA sequences that bind to the nuclear matrix, a network of nonhistone proteins within the nucleus |
| Microdomains | Loops of bacterial chromosomal DNA, typically 10 kbp in length, that emanate from a central core. |
| Moderately repetitive sequences | DNA sequences that are found a few hundred to several thousand times in a genome. |
| nonautonomous elements | A transposable element that lacks a gene that encodes a protein (such as transposase or reverse transcriptase) that is necessary for transposition. |
| non-LTR retrotransposons | A type of retrotransposon that does not have long terminal repeats. |
| Nuclear lamina | protein meshwork that provides mechanical support to the nucleus and regulates many nuclear processes |
| Nuclear matrix | 3d protein network in the nucleoplasm that organizes chromatin and supports transcription and replication |
| Nucleoid-associated proteins (NAPs) | set of DNA-binding proteins that are found in bacteria and facilitate compaction and organization of the chromosome. |
| Origin of replication | A nucleotide sequence that functions as an initiation site for the assembly of several proteins required for DNA replication. |
| Protein-encoding genes | A gene that encodes apolypeptide; also called a structural gene. |
| Radial loop domains | A segment of chromatin that is organized into a loop. |
| Repetitive sequences | Short DNA sequences that are present in many copies in the genome. |
| Retrotransposon | A type of transposable element that moves via an RNA intermediate. |
| Retrotransposition | A form of transposition in which the transposable element is transcribed into RNA. The RNA is then used as a template via reverse transcriptase to synthesize a DNA molecule that is integrated into a new region of the genome via integrase. |
| Reverse Transcriptase | enzyme that uses an RNA template to make a single-stranded or double-stranded DNA molecule. |
| Simple transposition | A cut-and-paste mechanism for transposition in which a transposable element is removed from one site and inserted into another. |
| simple transposon | transposon that moves via simple transposition and carries additional genes that are not required for transposition, such as an antibiotic resistance gene. |
| Tandem array | A short nucleotide sequence that is repeated many times in a row. |
| Topoisomers | DNA conformations that differ only with regard to supercoiling. |
| Transposable elements (TEs) | short segment of DNA that can move to multiple locations within the chromosomal DNA. |
| Transposase | The enzyme that catalyzes the movement of transposons. |
| ARS elements | DNA sequences found in yeast that function as origins of replication. |
| Bidirectional replication | DNA replication, describes the movement of the two replication forks in opposite directions outward from the origin of replication. |
| Conservative model | An incorrect model that proposed that both strands of parental DNA remain together following DNA replication. |
| Dispersive model | incorrect model for DNA replication that proposed that segments of parental DNA and newly made DNA are interspersed in both strands following the replication process. |
| DNA gap repair synthesis | synthesis of DNA in a region where a DNA strand has been previously removed, usually by a DNA repair enzyme or by an enzyme involved in homologous recombination. |
| DNA gyrase | An enzyme that alters the degree of supercoiling in DNA by relaxing negative supercoils. |
| DNA helicase | An enzyme that separates the two strands of DNA. |
| DNA ligase | enzyme that catalyzes the formation of a covalent bond between two DNA fragments |
| DNA polymerase | enzyme that catalyzes the covalent attachment of nucleotides to form a strand of DNA. |
| DNA replication | process in which original DNA strands are used as templates for the synthesis of new DNA strands. |
| DnaA proteins | protein that binds to the DnaA box at the origin of replication in bacteria and initiates DNA replication. |
| flap endonuclease | endonuclease found in eukaryotes that removes flaps that are generated during DNA replication. |
| GATC methylation sites | DNA sequence in bacteria that is methylated; it plays a role in preventing DNA replication from happening too early. |
| genetic recombination | 1) the process in which chromosomes are broken and then rejoined to form a new genetic combination; 2) the process in which alleles are assorted and passed to offspring in combinations that are different from those in the parents |
| heteroduplex | double-stranded region of DNA that contains one or more base pair mismatches. |
| Holliday junction | site where an unresolved crossover has occurred between two homologous chromosomes. |
| Holliday model | model to explain the molecular mechanism of homologous recombination. |
| Homologous recombination | exchange of DNA segments with similar or identical DNA sequences, such as those in homologous chromosomes. |
| lagging strand | strand that is synthesized during DNA replication as short Okazaki fragments in the direction away from the replication fork. |
| leading strand | strand that is synthesized during DNA replication continuously in the same direction as the replication fork is moving. |
| Okazaki fragments | Short segments of DNA that are synthesized to form the lagging strand during DNA replication. |
| Origin recognition complex (ORC) | complex of six proteins found in eukaryotes that is necessary to initiate DNA replication. |
| Prereplication complex (preRC) | eukaryotes, an assembly of at least 14 different proteins, including a group of 6 proteins called the origin recognition complex (ORC), that acts as the initiator of eukaryotic DNA replication. |
| Primase | enzyme that synthesizes a short RNA primer during DNA replication. |
| Primosome | multiprotein complex composed of DNA helicase, primase, and several accessory proteins. |
| Processing enzyme | enzyme, such as RNA or DNA polymerase, that glides along the DNA and does not dissociate from the template strand as it catalyzes the covalent attachment of nucleotides. |
| proofreading | ability of DNA polymerase to remove mismatched bases from a newly made strand. |
| replication fork | region where two DNA strands have separated and new strands are being synthesized. |
| replisome | complex that contains a primosome and dimeric DNA polymerase. |
| RNA primer | A short strand of RNA, made by primase, that is used to elongate a strand of DNA during DNA replication. |
| semiconservative model | The correct model for DNA replication that proposes that the newly made double-stranded DNA contains one parental strand and one daughter strand. |
| single-strand binding proteins | protein that binds to both of the single strands of DNA during DNA replication and prevents them from re-forming a double helix. |
| Sister chromatid exchange (SCE) | phenomenon in which crossing over occurs between sister chromatids, which thereby exchange identical genetic material. |
| template strands | A strand of DNA that is used to synthesize a complementary strand of DNA or RNA. |
| Telomerase | protein/RNA complex that recognizes telomeric sequences at the ends of eukaryotic chromosomes and synthesizes additional repeats of those sequences. |
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