Definitions Flashcards
CO-DOMINANT
When two alleles are both dominant and both alleles show up in the phenotypes.
(Eg. Red petal allele and blue petal allele are both dominant, flower ends up with both red and blue petals.)
F2 generation = 1:2:1 ratio
CARRIER
Someone who has inherited a recessive allele for a genetic trait or mutation but does not display that trait or show symptoms of the disease.
CHIASMA
A point of attachment between chromosomes at which crossing over takes place
SEX LIMITED CHARACTERISTICS
Sex limited genes are genes present in both sexes of sexually reproducing species but are expressed in only one sex and remain ‘turned off’ in the other
LYON HYPOTHESIS
Proposed by Mary Lyon in 1961, this hypothesis proposes that one X chromosome in each female cell becomes inactivated (a Barr body) and suggests that which of the X chromosomes because inactivation is random and varies from cell to cell
EPISTASIS
Only a single copy of an allele is required to inhibit the expression of an allele at a different locus. Type of gene interaction in which a gene at one loves masks or suppresses the expression of another gene at a different locus.
Basically when one gene depends on another gene for it to be expressed.
PEDIGREE
Pictorial representation of a family history outlining the inheritance of one or more traits or diseases. (The flow charts using boxes and circles etc)
TURNER SYNDROME
Human condition in which cells contain a single X chromosome and no Y chromosome (XO). Persons with this syndrome appear female but do not undergo puberty and have poorly developed female secondary sex characteristics; most are sterile but have normal intelligence
CARRIER
Someone who has inherited a recessive allele for a genetic trait or mutation but does not display that trait or show symptoms of the disease
HETEROZYGOUS
Two different alleles/genes at a locus. One is dominant and one is recessive. (Eg. Blue eye gene and a brown eye gene)
SEX-LINKED CHARACTERISTIC
Genes are present in both sexes but only expressed in one sex (Eg. Lactation)
KLINEFELTER SYNDROME
Human condition in which cells contain one or more Y chromosomes along with multiple X chromosomes (most commonly XXY, but may also be XXXY, XXXXY or XXYY).
People with this syndrome appear male but frequently have small testes, some breast enlargement, reduced facial and pubic hair, are often tall but sterile and most have normal intelligence.
HYPOSTATIC
The gene which is suppressed
ALLELE
Each of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome
HOMOZYGOUS
Two of the same genes/alleles at a locus (Eg. Both code for blue eyes)
DIOECIOUS
Either male or female reproductive structures in one organism (humans)
PENETRANCE
The percentage of individuals possessing a genotype and expressing the phenotype.
(Eg. If you’re homozygous for haemochromatosis, only a certain percentage of people will express those alleles. So penetrance is not 100%
MONOECIOUS
Both male and female structures in the same organism
MULTIPLE ALLELES
Mendel looked at genes for which there were only 2 alleles. Though, there can be 3-100 for one gene (Eg. The ABO blood grouping system, however one person can only have 2 of the possible alleles) - because you can only have 2 of each type of chromosome.
PHENOCOPY
A trait that is determined by an environmental effect and has the same phenotype as a genetically determined trait.
Example: Bunnies who get the dark fur around extremities in colder climates.
Y-LINKED CHARACTERISTIC
Characteristic determined by a gene or genes on the
Y-chromosome
POLY-X-FEMALES
Many X’s and no Y’s
MUTATION
Heritable (capable of being inherited) change in genetic information.
GENETIC MATERNAL EFFECT
Phenotype of offspring is determined by genotype of mother. (Eg. The spiral direction of snail shells)
PLEIOTROPHY
When a single genotype influences multiple phenotypes.
DOSAGE COMPENSATION
In placental mammals, dosage compensation is accomplished by the random inactivation of one X chromosome in the cells of females so that the cell isn’t producing twice the amount of proteins due to females having 2 X chromosomes
RECESSIVE EPISTASIS
The presence of two recessive alleles inhibits the expression of an allele at a different locus (homozygous genotype)
AUTOSOMAL
A chromosome that is NOT a sex chromosome
GENETIC VARIATION
Phenotype variance that is due to genetic differences among individual members of population.
- Crossing over
- Random distribution (meiosis)
X-LINKED CHARACTERISTICS
A characteristic determined by a gene or genes on the
X-chromosome
CONTINUOUS TRAIT
Multiple genes contribute. Display a continuum of different varieties such as human height. Many different possible heights.
(Quantitative traits)
EPISTATIC
Gene which is doing the suppressing
DOMINANT EPISTASIS
Only a single copy of an allele is required to inhibit the expression of an allele at a different locus
POLY-X-FEMALES
Many X’s and no Y’s
EPIGENETICS
Changes in gene expression and/or a phenotype that are potentially heritable without alteration of the underlying DNA base sequence.
ANDROGEN INSENSITIVITY SYNDROME
Has Y chromosome but faulty androgen receptors so at birth, baby looks like a girl.
INCOMPLETE DOMINANCE
A blend (Eg. Red + White = Pink) 1:2:1 ratio
GENOMIC IMPRINTING
When one copy of a gene is silenced due to its parental origin
ALLELE
Each of two or more alternate forms of a gene that arise by mutation and are found at the same place on a chromosome
HEMIZYGOUS
Having only a single copy of a gene instead of the customary two copies. All the genes on the single X chromosome in the male are “hemizygous”.
NON-DISJUNCTION
Failure of homologous chromosomes or sister chromatids to separate in meiosis or mitosis
EXPRESSIVITY
The degree to which a trait is expressed
LETHAL ALLELES
Causes the death of an individual organism, often early in development and so the organism does not appear in the progeny of a genetic cross.
• Recessive lethal alleles only kill individual organisms that are homozygous for the allele.
• Dominant lethal alleles kill both heterozygotes and homozygotes.
GENE INTERACTION
Interaction between genes at different loci that affect the same characteristic
SEX INFLUENCED
Determined by autosomal genes and are inherited according to Mendel’s principals but they are expressed differently in males and females.
(Eg. male pattern baldness)
ANTICIPATION
Increasing severity or earlier age of onset of a genetic trait in succeeding generations.
For example, symptoms of a genetic disease may become more severe as the trait is passed from generation to generation.
CYTOPLASMIC INHERITANCE
Inheritance of characteristics encoded by genes located in the cytoplasm. Because the cytoplasm is usually contributed entirely by only one parent, most cytoplasmically inherited characteristics are inherited from a single parent. (Basically this is mitochondrial DNA inheritance).
DISCONTINUOUS TRAIT
“Either/Or” - Mendel had either yellow OR green peas and either round OR wrinkled peas.
(Qualitative traits)
COMPLEMENTATION
Parents who are homozygous for DIFFERENT mutations are crossed, offspring are heterozygous. If mutations occur on same locus, the heterozygous
If occur on different loci, each parent has wild type gene on other locus, so heterozygous offspring will inherit mutant allele & wild type allele complements, so wild type phenotype.
CONSANGUINITY
Mating between related individuals (inbreeding)
INBREEDING DEPRESSION
Decreased fitness arising from inbreeding (often due to increased expression of lethal or deleterious recessive traits)
HYBRID VIGOUR
Reduced number of recessive problems due to inbreeding
DIZYGOTIC TWINS
Non identical.
MONOZYGOTIC TWINS
Identical.
CONCORDANT
Refers to a pair of twins with whom have the same trait under consideration.
POLYMERASE CHAIN REACTION (PCR)
A technique used to amplify particular genes within an embryo
SINGLE NUCLEOTIDE POLYMORPHISM (SNP)
Single base pair differences in DNA sequence between individual members of a species. (Variants)
TRANSMISSION GENETICS
Field of genetics that encompasses the basic principles of genetics and how traits are inherited.
POPULATION GENETICS
Study of the genetic composition of populations (groups of members of the same species) and how a population’s collective group of genes changes with the passage of time.
MOLECULAR GENETICS
Study of the chemical nature of genetic information and how it is encoded, replicated, and expressed.
PREFORMATIONISM
Early concept of inheritance proposing that a miniature adult (homunculus) resides in either the egg or the sperm and increases in size in development, with all traits being inherited from the parent that contributes the homunculus.
PANGENESIS
Early concept of heredity proposing that particles carry genetic information from different parts of the body to the reproductive organs.
GERM-PLASM THEORY
States that cells in the reproductive organs carry a complete set of genetic information.
INHERITANCE OF ACQUIRED CHARACTERISTICS
Early notion of inheritance proposing that acquired traits are passed to descendants.
BLENDING INHERITANCE
Early concept of heredity proposing that offspring possess a mixture of the traits from both parents.
LINKAGE GROUP
Genes located close together on a chromosome are called “linked genes” and belong to the same linkage group.
Linked genes WON’T give 9:3:3:1 ratio on dihybrid cross, it’ll give variations because the genes are linked.
TEST CROSS
A cross between an individual with an unknown genotype and an individual with the homozygous recessive genotype.
CIS-CONFORMATION (COUPLING PHASE)
Arrangement in which two or more wild-type genes are on one chromosome and their mutant alleles are on the homologous chromosome; also called coupling configuration.
AB/ab
TRANS-CONFORMATION (REPULSION PHASE)
Arrangement in which each chromosome contains
one wild-type (dominant) gene and one mutant (recessive) gene; also called repulsion.
Ab/aB
RECOMBINANT GAMETE
Possesses new combinations of genes.
NON-RECOMBINANT GAMETE
Contains only the original combinations of genes present in the parents.
MAP UNITS (m.u.)
Unit of measure for distances on a genetic map; 1 map unit equals 1% recombination.
TWO-POINT TESTCROSS
Cross between an individual heterozygous at two loci and an individual homozygous for recessive alleles at those loci.
HAPLOTYPE
The specific set of SNPs and other genetic variants observed on a single chromosome. SNPs within a haplotype are physically linked and therefore tend to be inherited together.
LINKAGE DISEQUILIBRIUM
Two different genes, for example being a psycho and having red hair. They’re completely unrelated and not mutually exclusive but they are often inherited together because they’re close in location on the chromosome.
SOMATIC CELL HYBRIDISATION
Somatic cells fused to form hybrids. (Can be used for mapping - positioning genes on chromosomes)
Eg. Fusing a mouse tumour cell with a fibroblast using polyethylene glycol.
(After fusion = 2 nuclei & is called a heterokaryon… eventually 2 nuclei fuse too)
DELETION MAPPING
Technique for determining the chromsomal location of a gene by studying the association of its phenotype or product with particular chromosome deletions.
- If the gene is in region of deletion or not in region of deletion, you can tell.
ANEUPLOIDY
A chromosomal abnormality where we have either one extra copy of a chromosome (trisomic) or one less copy of a chromosome (monosomic) than we should.
POLYPLOIDY
Polyploidy is found in organisms who instead of having a pair of each chromosome (diploid) they have 3 or more homologous chromosomes (for all chromosomes).
Spindles don’t form properly and ALL chromatids end up in one cell.
TRANSLOCATION
A segment of one chromosomes moves to another chromosome
Non reciprocal - move from one chromosome to another without reciprocal movement.
Reciprocal - two way movement.
PSEUDODOMINANCE
Expression of a normally recessive allele due to a
deletion on the homologous chromosome.
HAPLOINSUFFICIENCY
The phenomenon where a diploid organism has only a single functional copy of a gene (with the other copy inactivated by mutation) and the single functional copy of the gene does not produce enough gene product (typically a protein) to bring about a wild-type condition, leading to an abnormal or diseased state.
PARACENTRIC INVERSIONS
Chromosome inversion that does not include the centromere in the inverted region.
PERICENTRIC INVERSIONS
Chromosome inversion that includes the centromere in the inverted region.
NULLISOMY
Loss of both copies of homologous chromosomes
MONOSOMY
Loss of a single chromosome (like Turner’s Syndrome who are XO)
TRISOMY
Gain of a single chromosome (so three instead of two homologues). Eg. Down Syndrome (Trisomy 21)
TETRASOMY
Gain of two homologous chromosomes
NON DISJUNCTION
Failure of homologous chromosomes or sister chromatids to separate in meiosis or mitosis. So both homologous chromatids go into one cell and none of them go into the other.
EUPLOID
Normal number of chromosomes.
UNIPARENTAL DISOMY
Both homologues of a chromosome are inherited by the same parent.
AUTOTETRAPLOID
A diploid (2n) cell going through mitosis, non disjunction occurs and you end up with a 4n cell.
ALLOPOLYPLOIDY
Hybridisation between two species resulting in polyploid species carrying chromosomes sets from two or more species.
(Not to be confused with AUTOpolyploidy)
Eg. Tiger + Lion = Liger
AUTOPOLYPLOIDY
Polyploidy in which extra chromosome sets are derived from two or more DIFFERENT species.
(Not to be confused with ALLOpolyploidy)
Caused by accidents of mitosis and meiosis.
POLYGENIC TRAIT
Encoded by genes at many loci. (Polygeny)
RECOMBINATION
Process that produces new combinations of alleles. When one of the F1 progeny reproduces the combination of its alleles in IT’S gametes may differ from it’s parents.
HETEROKARYON
When two cells fuse to become one cell with two nuclei it is called a heterokaryon.
PALINDROMIC
A word, line, verse, number or sentence etc, reading the same backward as forward.
Eg. “MADAM” or “RADAR”
POSITIVE SUPERCOIL (DNA)
Over rotation
NEGATIVE SUPERCOIL (DNA)
Under rotation (most often)
CHROMOSOME
Structure consisting of DNA and associated proteins that carries and transmits genetic information.
CHROMATIN
Material found in the eukaryotic nucleus; consists of DNA and proteins.
EUCHROMATIN
Chromatin that undergoes condensation and decondensation in the course of the cell cycle. (Opens up and closes because if DNA is too tightly packed, enzyme can’t get in to replicate.)
HETEROCHROMATIN
Chromatin that remains in a highly condensed state throughout the cell cycle; found at the centromeres and telomeres of most chromosomes
TELOMERE
Stable end of a chromosome.
CENTROMERE
Constricted region on a chromosome that stains less strongly than the rest of the chromosome; region where spindle microtubules attach to a chromosome.
NUCLEOSOME
Basic repeating unit of chromatin, consisting of a core of eight histone proteins (two each of H2A, H2B, H3, and H4) and about 146 bp of DNA that wraps around the core about two times.
SUPERCOIL
Coiled tertiary structure that forms when strain is placed on a DNA helix by overwinding or underwinding of the helix. An overwound DNA exhibits positive supercoiling; an underwound DNA exhibits negative supercoiling.
TRANSPOSABLE ELEMENT
DNA sequence capable of moving from one site to another within the genome through a mechanism that differs from that of homologous recombination.
NUCLEOSOMES
DNA complexed with histones = nucleosomes.
A core of eight histone proteins (two each of H2A, H2B, H3, and H4) and about 146 bp of DNA that wraps around the core about two times.
CHROMOSOMAL PUFF
Localized swelling of a polytene chromosome; a region of chromatin in which DNA has unwound and is undergoing transcription.
POLYTENE CHROMOSOME
Giant chromosome in the salivary glands of Drosophila melanogaster. Each polytene chromosome consists of a number of DNA molecules lying side by side.
C VALUE
The amount of DNA per cell for a specific organism
SEMICONSERVATIVE
Replication in which the two nucleotide strands of DNA separate, each serving as a template for the synthesis of a new strand. All DNA replication is semiconservative.
So two new strands = 1 parent strand and 1 new strand
LEADING STRAND
DNA strand that is replicated continuously.
LAGGING STRAND
DNA strand that is replicated discontinuously.
TEMPLATE STRAND
The strand of DNA that is used as a template during transcription. The RNA synthesized during transcription and daughter DNA strand synthesized during replication is complementary and antiparallel to the template strand.
BIDIRECTIONAL
Replication at both ends of a replication bubble.
REPLICATION BUBBLE
Segment of a DNA molecule that is unwinding and undergoing replication.
OKAZAKI FRAGMENTS
Discontinuously synthesized short DNA fragments forming the lagging strand.
REPLICATION FORK
Point at which a double-stranded DNA molecule separates into two single strands that serve as templates for replication.
PRIMER
A short piece of RNA with a 3’ OH group that binds to DNA so other nucleotides can be added. (Usually 10-12 nucleotides long) - Lagging strand has many of these.
PROOFREADING
Ability of DNA polymerases to remove incorrectly paired nucleotides and replace with correct nucleotides in the course of replication.
AUTONOMOUSLY REPLICATING SEQUENCE (ARS)
DNA sequence that posses the ability to replicate; contains an origin of replication.
ORIGIN RECOGNITION COMPLEX (ORC)
A multi protein complex which binds to origins of replication of autonomously replicating sequence (ARS) and directs DNA replication throughout the genome and is required for its initiation
MINICHROMOSOME MAINTENANCE (MCM)
“Licensing factors” - they give origin recognition complexes (ORCs) ‘permission’ to bind to autonomously replicating sequences (ARS).
Basically says “Right, ARS, you’re open for business”… once ARS is open for business, ORC can bind.
HOMOLOGOUS RECOMBINATION
Type of genetic recombination in which nucleotide sequences are exchanged between two similar or identical molecules of DNA. It is most widely used by cells to accurately repair harmful breaks that occur on both strands of DNA, known as double-strand breaks
*Double strand breaks caused by ionising radiation, oxidative free radicals, other DNA damaging agents.
TELOMERASE
Enzyme that is made up of both protein and RNA and replicates the ends (telomeres) of eukaryotic chromosomes. The RNA part of the enzyme has a template that is complementary to repeated sequences in the telomere and pairs with them, providing a template for the synthesis of additional copies of the repeats. So the DNA strand doesn’t lose length with every division, (which eventually leads to cell death). Cells which contain telomerase avoid apoptosis.
(Present in stem cells and cancer cells)
RIBOSOMAL RNA (rRNA)
A ribosome is a complex within all living cells that serves as the site ofbiological protein synthesis. Ribosomal RNA is theRNAcomponent of theribosome, and is essential forprotein synthesisin all living organisms.
TRANSFER RNA (tRNA)
RNA molecule that carries an amino acid to the ribosome and transfers it to a growing polypeptide chain in translation as directed by a three-nucleotide sequence in mRNA.
MESSENGER RNA (mRNA)
RNA molecule that carries coding instructions for polypeptide chains from DNA to a ribosome.
This is the RNA which is MADE during transcription.
REPLICON
Individual sections of replication, each contains an origin of replication.
CODING STRAND
The strand of DNA whose base pairs are being read in transcription and replication.
PROMOTER
Promotersequences areDNAsequences that define where transcription of a gene by RNA polymerase begins.Promotersequences are typically located directly upstream or at the 5’ end of the transcription initiation site.
Transcription apparatus recognises and binds to the promoter.
INITIATION
Duringinitiation, proteins bind to the origin ofreplicationand causes a short section of DNA to unwind. This unwinding allows helicase and other single strand binding proteins to attach to the polynucleotide strand.
TERMINATION
DNA replication is terminated whenever two replication forks meet OR at certain termination sequences (called Ter sites). A termination protein binds to these sequences creating a complex and blocks movement of helicase, stalling the replication fork and preventing further DNA replication.
TRANSCRIPTION START SITE
The first DNA nucleotide that is transcribed into an RNA molecule.
PRIMERS
Short stretches of RNA nucleotides (about 10-12) which provide a 3’ OH group to which DNA polymerase can attach DNA nucleotides.
GENETIC MAP
Provide a rough approximation of the locations of genes relative to the locations of other known genes. Chromosome maps calculated by using the genetic phenomenon of recombination.
Distance on genetic maps are measured in percent recombination (centimorgans, cM) or map units (m.u.)
POSITION EFFECT
Many genes are regulated in a position-dependent manner; if their positions are altered by an inversion, they may be expressed at inappropriate times or in inappropriate tissues.
AUTOTRIPLOID
Having 3n instead of 2n chromosomes.
ALLOTRIPLOID
Having three sets of chromosomes derived from different species.
LOD SCORE
A statistical estimate of whether two loci (the sites of genes) are likely to lie near each other on a chromosome and are therefore likely to be inherited together as a package. LOD stands for logarithm of the odds (to the base 10).
CONSENSUS SEQUENCES
A sequence of DNA having similar structure and function in different organisms. It positions RNA polymerase so that the enzymes active site is aligned for the initiation of transcription over the “start site” (position +1).
BASAL TRANSCRIPTION APPARATUS
A group of proteins that assemble near the start site and are sufficient to initiate minimal levels of transcription.
- General transcription factors plus RNA polymerase = basal transcription apparatus.
CO-LINEARITY
Concept that the number of nucleotides in the gene is proportional to the number of amino acids in the protein and that a continuous sequence of nucleotides in the DNA codes for a continuous sequence of amino acids in the protein.
NON CO-LINEARITY
Concept that coding sequences in a gene may be interrupted by noncoding sequences and that the coding sequence in a gene is NOT always continuous.
INTRON
Intervening sequence in a split gene; removed from the RNA after transcription.
EXON
Coding region of a split gene (a gene that is interrupted by introns). After processing, the exons remain in messenger RNA.
POLYADENYLATION
The addition of multiple Adenines to the end of an RNA molecule to form the Poly-A tail.
BRANCH POINT
An adenine nucleotide in pre-mRNA that lies from 18 to 40 nucleotides upstream of the 3′ splice site within an intron.
LARIAT
Looplike structure created in the splicing of pre-mRNA in which the 5′ end of an intron is attached to a branch point in pre-mRNA.
It forms a lariat to prevent it from tethering to “machinery”
SPLICEOSOME
Large complex consisting of several RNAs and many proteins that is responsible for splicing pre-mRNA. (Splices introns that aren’t self splicing - Group 1 and 2 are self splicing)
Contains five small ribonucleoprotein particles (U1, U2, U4, U5, and U6).
ALTERNATIVE SPLICING
Process by which a single pre-mRNA can be spliced in more than one way to produce different types of mRNA. So you wind up with different types of exons included in RNA (and some or none are removed with lariat)
MULTIPLE 3’ CLEAVAGE SITES
Refers to the presence of more than one
3′ cleavage site on a single pre-mRNA, which allows cleavage and polyadenylation to take place at different sites, producing mRNAs of different lengths.
ALTERNATIVE PROCESSING PATHWAY
One of several pathways by which a single pre-mRNA can be processed in different ways to produce alternative types of mRNA.
For example: Calcitonin in the thyroid or CGRP in the brain.
GUIDE RNA (gRNA)
RNA molecule that serves as a template for an alteration made in mRNA during RNA editing. A gRNA contains sequences that are partly complementary to segments of the pre edited RNA and the two undergo base pairing in these sequences.
RNA-INDUCED SILENCING COMPLEX
Combination of a small interfering RNA (siRNA) molecule or a microRNA (miRNA) molecule and proteins that can cleave mRNA, leading to the degradation of the mRNA, or affect transcription or repress translation of the mRNA.
SMALL INTERFERING RNA (siRNA)
Single-stranded RNA molecule (usually from 21 to 25 nucleotides in length) produced by the cleavage and processing of double-stranded RNA; binds to complementary sequences in mRNA and brings about the cleavage and degradation of the mRNA. Some siRNAs bind to complementary sequences in DNA and bring about their methylation.
Come from the cleavage of mRNAs and can be both local or foreign derived (Eg. viruses)
MICRO RNA (miRNA)
Small RNA molecule, typically 21 or 22 bp in length, produced by cleavage of double-stranded RNA arising from small hairpins within RNA that is mostly single stranded. The miRNAs combine with proteins to form a complex that binds (imperfectly) to mRNA molecules and inhibits their translation.
Come from introns or exons of pre-mRNA. All internally produced.
GENE
All sequences in DNA that are transcribed into a single RNA molecule.
DNA HELICASE
Enzyme that unwinds double-stranded DNA by breaking hydrogen bonds.
TRANSCRIPTION UNIT
Sequence of nucleotides in DNA that encodes a single RNA molecule, along with the sequences necessary for its transcription; normally contains:
- Promoter
- RNA-coding sequence
- Terminator.
TRANSCRIPTIONAL ACTIVATOR PROTEINS
Protein in eukaryotic cells that binds to consensus sequences in regulatory promoters or enhancers and affects transcription initiation by stimulating the assembly of the basal transcription apparatus.
MONOCISTRONIC
Describing a type of messenger RNA that can encode only one polypeptide per RNA molecule. (Eukaryotes)
POLYCISTRONIC
Describing a type of messenger RNA that can encode more than one polypeptide separately within the same RNA molecule. (Prokaryotes)
SHINE-DALGARNO SEQUENCE
A consensus sequence in PROKARYOTIC mRNA (UAAGGAGGU) which is a ribosome binding site during translation as the sequence is complementary to and pairs with sequences found in one of the RNA molecules that make up the ribosome.
This is kind of like their version of a 5’ cap - our 5’ cap allows ribosome to bind.
SENSE CODON
Codon that specifies an amino acid in a protein.
DEGENERATE CODE
Refers to the fact that the genetic code
contains more information than is needed to specify all 20 common amino acids.
SYNONYMOUS CODONS
Differing codons that specify the same amino acid.
ISOACCEPTING tRNAs
Different tRNA molecules that accept the same amino acid but have different anticodons.
INITIATION CODON
The first codon of the mRNA to specify an amino acid. Most commonly AUG (methionine). GUG and UUG used rarely.
TANDEM REPEAT SEQUENCES
DNA sequences repeated one after another; tend to be clustered at specific locations on a chromosome.
SATELLITE DNA
Highly repetitive DNA which is the main component of functional centromeres and form the main structural constituent heterochromatin.
OPERON
Set of structural genes in a bacterial cell along with a common promoter and other sequences (such as an operator) that control the transcription of the structural genes.
SPACER DNA
A region of non-coding DNA between genes.
TRANSLATION
Process by which a protein is assembled from information contained in messenger RNA.
PEPTIDE BOND
Chemical bond that connects amino acids in a protein.
CODON
Sequence of three nucleotides that encodes one amino acid in a protein.
ANTICODON
Sequence of three nucleotides in transfer RNA that pairs with the corresponding codon in messenger RNA in translation.
WOBBLE
Base pairing between codon and anticodon in which there is nonstandard pairing, usually at the third (3′) position of the codon; allows more than one codon to pair with the same anticodon.
GENETIC CODE
The genetic code is a set of rules defining how the four-letter code of DNA is translated into the 20-letter code of amino acids, which are the building blocks of proteins. The genetic code is a set of three-letter combinations of nucleotides called codons, each of which corresponds to a specific amino acid or stop signal.
AMINO ACID
Repeating unit of proteins; consists of an amino group, a
carboxyl group, a hydrogen atom, and a variable R group.
All have the same basic structure, only the R group differs.
DEGENERATE
Particular amino acids are specified by multiple codons. (Synonymous codons, isoaccepting tRNA, wobble at third base)
Eg. UCC and UCU both code for serine. The anticodon on the tRNA for serine is AGG… AGG should bind to UCC, but on UCU there is a “wobble position” between the final G-U bond), they still bind because the other two pairs bind.
NONESENSE MEDIATED mRNA DECAY (NMD)
Process that brings about the rapid elimination of mRNA that has a premature stop codon.
The mRNA is rapidly deleted.
STALLED RIBOSOMES AND NONSTOP mRNA (SR)
Occurs when there is no termination codon in the mRNA (due to mutated codon or truncated mRNA)
In prokaryotes = Stalled Ribosomes
In eukaryotes = Non stop mRNAs.
Ribosome gets to 3’ end of mRNA, stalls (because releasing factor can’t bind to release the polypeptide because there is no site for it to bind to) and a fake mRNA is added to restart translation to finish it off.
NO-GO DECAY (NGD)
Mechanism used by eukaryotes to degrade the mRNA and recycle the ribosome in case of stalled ribosomes.
TRUNCATED
Cut short
TRANSFER MESSENGER RNA (tmRNA)
The “fake mRNA” created in the case of stalled ribosomes.
CHAPERONE PROTEIN
Polypeptide chains can fold automatically to reach a low energy state.
Chaperone proteins are proteins which help the polypeptide chain fold correctly.
DIHYBRID CROSS
A cross between two individuals that differ in two characteristics—more specifically, a cross between individuals that are homozygous for different alleles at the two loci (AA BB × aa bb); also refers to a cross between two individuals that are both heterozygous at two loci (Aa Bb × Aa Bb).
POINT MUTATION
A mutation where there is a change in a single nucleotide (deletion, insertion, substitution).
MUTAGEN
Any environmental agent that significantly increases the rate of mutation above the spontaneous rate.
MUTATION
An inherited change in DNA sequence which cannot normally be repaired.
SUBSTITUTION MUTATION
A mutation where a nucleotide change alters a single codon in the gene.
FRAMESHIFT MUTATION
Alters the reading frame of a gene. (Base insertion or base deletion, shifts all other bases along to completely change the reading frame).
MISSENSE MUTATION
A type of base substitution mutation which alters a codon in mRNA, resulting in a different amino acid in the protein encoded.
NONSENSE MUTATION
A type of base substitution mutation that changes a sense codon (one that specifies an amino acid) into a stop codon - so premature ‘stop’ codon.
SILENT MUTATION
A type of base substitution mutation where a codon is changed to a synonymous codon that specifies the same amino acid.
EXPANDING TRINUCLEOTIDE REPEATS
Mutation in which the number of copies of a set of nucleotides (most often three nucleotides) increases in succeeding generations.
Examples to remember: Huntington’s Disease and Fragile X Syndrome.
NEUTRAL MUTATIONS
Type of missense mutation (base substitution mutation) which alters the amino acid sequence of a protein but doesn’t significantly change function.
LOSS OF FUNCTION MUTATION
A type of base substitution mutation which causes complete or partial loss of normal function (often recessive in expression)
GAIN OF FUNCTION MUTATION
A type of base substitution mutation which produces a new trait (often dominant in expression)
LETHAL MUTATION
A type of base substitution mutation which causes premature death - Eg. Sickle cell, Huntington’s disease.
CONDITIONAL MUTATION
A type of base substitution mutation that is only expressed under certain conditions (Eg. temperature)
SUPPRESSOR MUTATION
Mutation that hides or suppresses the effect of another mutation at a site that is distinct from the site of the original mutation.
- *Intragenic - Occur in the same gene.
- *Intergenic - Mutation in a second gene compensates for the first and restores the phenotype.
MUTATION RATE
The frequency that a wild type allele changes into a mutant allele
INSERTION
Mutation in which nucleotides are added to a DNA sequence.
MUTAGENESIS
A process by which the genetic information of an organism is changed, resulting in a mutation. It may occur spontaneously in nature, or as a result of exposure to mutagens. It can also be achieved experimentally using laboratory procedures.
CARCINOGEN
A substance capable of causing cancer in living tissue.
UNEQUAL CROSSING OVER
Misalignment of the two DNA molecules during crossing over, resulting in one DNA molecule with an insertion and the other with a deletion.
DELETION
Deletion of one or more nucleotides. Chemicals cause this (such as hydrogen peroxide)
MISMATCH REPAIR
A type of DNA repair mechanism:
Process that corrects mismatched nucleotides in DNA after replication has been completed. Enzymes excise incorrectly paired nucleotides from the newly synthesized strand and use the original nucleotide strand as a template when replacing them.
Mismatched pairs occur with protonation.
NUCLEOTIDE EXCISION REPAIR
A type of DNA repair mechanism:
Repairs many types of DNA damage by replacing a stretch of DNA.
BASE EXCISION REPAIR
DNA repair that first excises modified bases and then replaces the entire nucleotide.
DIRECT REPAIR
Changes altered nucleotides back to their original form using photolyases (which break thymidine dimers using energy from light) and alkylation of quinine repair by methyl transferases.
GENETIC DISSECTION
Finding or creating mutations that affect different components of a biological system and studying their effects, leading to the understanding of the system.
FORWARD MUTATION
A mutation that alters the wild-type phenotype (as opposed to a reverse mutation)
REVERSE MUTATION
Changes the mutant phenotype back into wild type.
SPONTANEOUS MUTATIONS
Occur under normal conditions
INDUCED MUTATIONS
Result from changes caused by environmental, chemical or radiation.
STRAND SLIPPAGE
A cause of deletion/insertion mutations when a nucleotide strand forms a small loop.
If the looped-out nucleotides are on the newly synthesized strand, an insertion results.
If the looped out nucleotides are on the template strand, a deletion results.
UNEQUAL CROSSING OVER
A cause of deletion/insertion mutations when during crossing over, the two chromosomes misalign and one crossover produces an insertion and the other has a deletion (so one ends up shorter and one ends up longer)
DEPURINATION
The loss of a purine from a nucleotide which can cause spontaneous mutations.
Results when the covalent bond connecting the purine to the carbon atom of the deoxyribose sugar breaks. It produces a site without a purine base and in replication, an incorrect nucleotide (most often adenine) is incorporated into the new strand.
DEAMINATION
The loss of an amino group (NH2) from a base. Can be induced or spontaneous.
It can alter the pairing properties of bases. For example, the deamination of cytosine produces uracil.
BASE ANALOGS
A class of chemical mutagens which are chemicals with structures similar to that of any of the four standard DNA bases. DNA polymerase cannot distinguish between these and standard bases so if they are present during replication, they may be incorporated into the new DNA molecules.
ALKYLATING AGENTS
A class of chemical mutagens which donate alkyl groups (such as methyl CH3 or ethyl CH3-CH2) to nucleotide bases. Eg. Mustard gas
STRUCTURAL GENOMICS
The organisation and sequence of genetic information contained within a genome.
STS
Sequence Tagged Site. A short (200 to 500 base pair) DNA sequence that occurs only once in the genome and whose location and base sequence are known.
STSs are detectable by polymerase chain reaction (PCR), are useful for localizing and orienting the mapping and sequence data, and serve as landmarks on the physical map of a genome.
CONTIG
Set of overlapping DNA fragments that have been assembled in the correct order to form a continuous stretch of DNA sequence.
TRANSCRIPTOME
Set of all RNA molecules transcribed from a genome.
GENOMIC WIDE ASSOCIATION STUDY (GWAS)
A study that attempts to correlate SNPs with a diseased state. Basically scan the entire genome to look for variants that may be associated with disease such as cancer, Crohn’s disease, macular degeneration etc. Mapped SNPs in affected people are compared with SNPs in unaffected people. (Only explains a small proportion of the genetic influence of the trait - environmental and epigenetic influences aren’t included)
EST
Expressed sequence tag. A short piece of DNA (cDNA = complementary DNA) that is complementary to an expressed mRNA transcript and is synthesized. It’s just a small piece, enough to bind the transcript.
Can be used to find active genes in a particular tissue or at a particular point in development.
CNV
Copy number variation. Difference among individual organisms in the number of copies of any large DNA sequence (larger than 1000 bp). Gene duplication or deletion resulting in a person having either only one copy (if deletion) or more than two copies (if duplication).
Can affect phenotype by altering dosage.
MICRO ARRAY
An ordered pattern of cDNA probes applied to a glass slide or silica chip. Might be 10,000-100,00 probes per few cm2 and each probe will be given a specific position so it can be found again and that probe will bind its complementary mRNA. So if its expressed you will see the probe.
To see it though, you will need to fluorescently label mRNA or label it another way.
Used to study which genes are active in particular tissues and also how gene expression changes in the course of biological processes such as development or disease progression.
RELATIVE FLUORESCENCE
Used in micro arrays as a comparison to see how much gene is expressed
TRANSPOSON
A sequence of DNA that can move to new positions within the genome of a single cell. The press called them jumping genes, but it is not correct to call them ‘genes’.
PROTEOMICS
Study of the proteome, the complete set of proteins found in a given cell. The proteome changes from cell to cell in an individual. We can use proteomics to identify when differential gene splicing has occurred and when post-translational modifications to proteins have occurred too.
GENOMICS
The field of genetics that attempts to understand the content, organisation, function and evolution of genetic information contained in whole genomes.
PHYSICAL MAP
Based on the direct analysis of DNA and they place genes in relation to distances measured in number of base pairs, kilobases (1000 base pairs) or megabases (1 million base pairs).
PROTEOME
All the proteins encoded by the genome.
METHYLATION
Addition of methyl groups to the nucleotide bases.
CpG ISLAND
DNA region that contains many copies of a cytosine base followed by a guanine base; often found near transcription start sites in eukaryotic DNA. The cytosine bases in CpG islands are commonly methylated when genes are inactive but are demethylated before the initiation of transcription.
POLYCOMB GROUP (PcG)
Special proteins that repress transcription by modifying histones (by either adding or removing histone modifications - acetyl groups, methyl groups etc)
PARAMUTATION
Interaction between two alleles that leads to a heritable change in the expression of one of the alleles…. This altered expression persists for several generations, even after the altering allele is no longer present.
EPIALLELES
Genetically identical alleles which produce heritable differences in phenotypes through epigenetic processes.
STEM CELLS
Undifferentiated cells that are capable of forming every type of cell in an organism (a property referred to as pluripotency).
MALIGNANT
Consists of cells that are capable of invading other tissues.
METASTASIS
Refers to cells that separate from malignant tumours and travel to other sites, where they establish secondary tumours.
ONCOGENES
Dominant-acting gene that stimulates cell division, leading to the formation of tumours and contributing to cancer; arises from mutated copies of a normal cellular gene (proto-oncogene).
TUMOUR-SUPPRESSOR GENES
Gene that normally inhibits cell division. Recessive mutations in such genes often contribute to cancer.
PROTO-ONCOGENE
Normal cellular gene that controls cell division. When mutated, it may become an oncogene and contribute to cancer progression.
SIGNAL-TRANSDUCTION PATHWAY
System in which an external signal (initiated by a hormone or growth factor) binds to a receptor on the outside of the cell and triggers a cascade of intracellular reactions that ultimately produce a specific response.
PROLIFERATION
Rapid increase in the number or amount of something such as a cell.
SEGREGATION
The separation of pairs of alleles at meiosis and their independent transmission via separate gametes.
PROVIRUS
DNA copy of viral DNA or viral RNA; integrated into the host chromosome and replicated along with the host chromosome.
HEMIMETHYLATED
When only one of the two strands of DNA is methylated.
lncRNA
Long Non Coding RNA - large and diverse class of transcribed RNA molecules with a length of more than 200 nucleotides that do not encode proteins (or lack > 100 amino acid open reading frame).
INDUCED PLURIPOTENT STEM CELLS
iPSCs - Fully differentiated adult cells that have been induced into reverting back into stem cells. Unfortunately they are not completely equivalent to embryonic stem cells because they contain an epigenetic imprint of where they came from.
SIGMA FACTOR
Subunit of bacterial RNA polymerase that allows the RNA polymerase to recognise a promoter and initiate transcription.
Holoenzyme = core enzyme + sigma binds to the -10 consensus sequence in bacterial promoter.
NON HOMOLOGOUS END JOINING
When sister chromatid isn’t available(usually in G phase). Uses proteins that recognises broken ends of DNA, binds to ends and joins them together.
More error prone and results in deletions, insertions and translocations.
*Caused by ionizing radiation, oxidative free radicals and other DNA damaging agents.
TRANSLESION DNA POLYMERASE
When distortion is found in DNA helix, translesion polymerases take over, though they are more error prone.
KARYOTYPE
Picture of an individual organism’s complete set of metaphase chromosomes.
CHROMOSOME DUPLICATION
Tandem - Duplicated area next to original area
Displace - Duplicated area fair way away from original
Reverse - Duplication is inversed.
TOPOISOMERASE
Enzyme that adds or removes rotations in a DNA helix by temporarily breaking nucleotide strands; controls the degree of DNA supercoiling.
INITIATOR PROTEINS
Bind to origin of replication & unwinds a short stretch of DNA allowing helicase & SSBPs to bind.
snRNA
Small Nuclear RNA. Also called a spliceosome. Small RNA molecule found in the nuclei of eukaryotic cells; functions in the processing of pre-mRNA.
- Contains 5 small ribonucleoprotein particles: U1, U2, U4, U5 & U6.
GENE
All sequences in DNA that are transcribed into a single RNA molecule.
AMINOACYL-tRNA SYNTHETASE
- A cell has 20 (one for each AA)
- Each synthetase recognises a particular AA as well as the tRNAs that accept that particular AA (recognises sizes, charges & R groups)
ELONGATION FACTOR G
Protein that combines with GTP and
is required for movement of the ribosome along the mRNA during translation.
ELONGATION FACTOR Tu
Forms a complex with GTP and a charged amino acid and then delivers the charged tRNA to the ribosome.
Xist GENE
Encodes lncRNA to coat inactive X chromosome and leads to the silencing of transcription of many genes on inactive X
Tsix GENE
(Xist backwards). Encodes lncRNA to inhibit transcription of Xist gene on ACTIVE x chromosome
Jpx GENE
Encodes lncRNA to stimulate the transcription of Xist on inactive X chromosome
Xite GENE
Encodes lncRNA to sustain Tsix gene expression on active X chromosome
RESTRICTION MAPPING
One technique used for creating physical maps. It determines the position of restriction sites on DNA.
PLURIPOTENCY
Undifferentiated cells which are capable of forming every type of cell in an organism.
TRANSITIONAL BASE SUBSTITUTION
A purine is replaced by different purine OR pyrimidine is replaced by different pyrimidine.
TRANSVERSION BASE SUBSTITUTION
A purine is replaced by a pyrimidine or vice versa
ALLELIC
Any of two or more variants of a gene that have the same relative position on homologous chromosomes and are responsible for alternative characteristics, such as smooth or wrinkled seeds in peas
