BIO 112 Exam 4

Allele

Gene variations that arise by mutation and exist at the same relative locations on homologous chromosomes

Autosomes

Any of the non-sex chromosomes

Codominance

In a heterozygote, complete and simultaneous expression of both alleles for the same characteristic

Continuous variation

Inheritance pattern in which a character shows a range of trait values with small gradations rather than large gaps between them

Dihybrid

Result of a cross between two true-breeding parents that express different traits for two characteristics

Discontinuous variation

Inheritance pattern in which traits are distinct and are transmitted independently of one another

Dominant

Trait which confers the same physical appearance whether an individual has two copies of the trait or one copy of the dominant trait and one copy of the recessive trait

Epistasis

Antagonistic interaction between genes such that one gene masks or interferes with the expression of another

F₁

First filial generation in a cross; the offspring of the parental generation

F₂

Second filial generation produced when F₁ individuals are self-crossed or fertilized with each other

Genotype

Underlying genetic makeup, consisting of both physically visible and non-expressed alleles, of an organism

Hemizygous

Presence of only one allele for a characteristic, as in X-linkage; hemizygosity makes descriptions of dominance and recessiveness irrelevant

Heterozygous

Having two different alleles for a given gene on the homologous chromosome

Homozygous

Having two identical alleles for a given gene on the homologous crhomosome

Hybridization

Process of mating two individuals that differ with the goal of achieving a certain characteristic in their offspring

Incomplete dominance

In a heterozygote, expression of two contrasting alleles such that the individual displays an intermediate phenotype

Law of independent assortment

Genes do not influence each other with regard to sorting of alleles into gametes; every possible combination of alleles is equally likely to occur

Law of segregation

Paired unit factors (i.e., genes) segregate equally into gametes such that offspring have an equal likelihood of inheriting any combination of factors

Linkage

Phenomenon in which alleles that are located in close proximity to each other on the same chromosome are more likely to be inherited together

Monohybrid

Result of a cross between two true-breeding parents that express different traits for only one characteristic

P₀

Parental generation in a cross

Phenotype

Observable traits expressed by an organism

Pleiotropy

A single gene producing one or more seemingly unrelated effects

Polygenic

A trait that is influenced by two or more genes

Product rule

Probability of two independent events occurring simultaneously can be calculated by multiplying the individual probabilities of each event occurring alone

Punnett square

Visual representation of a cross between two individuals in which the gametes of each individual are denoted along the top and side of a grid, respectively, and the possible zygotic genotypes are recombined at each box in the grid

Recessive

Trait that appears “latent” or non-expressed when the individual also carries a dominant trait for that same characteristic; when present as two identical copies, the recessive trait is expressed

Sex-linked

Any gene on a sex chromosome

Trait

Variation in the physical appearance of a heritable characteristic

X-linked

Gene present on the X, but not the Y chromosome

Deoxyribose

A five-carbon sugar molecule with a hydrogen atom rather than a hydroxyl group in the 2’ position; the sugar component of DNA nucleotides

DNA ligase

The enzyme that catalyzes the joining of DNA fragments together

DNA polymerase

An enzyme that synthesizes a new strand of DNA complementary to a template strand

Double helix

The molecular shape of DNA in which two strands of nucleotides wind around each other in a spiral shape

Helicase

During replication, this enzyme helps to open up the DNA helix by breaking the hydrogen bonds

Induced mutation

Mutation that results from exposure to chemicals or environmental agents

Lagging strand

During replication, the strand that is replicated in short fragments and away from the replication fork

Leading strand

Strand that is synthesized continuously in the 5’-3’ direction, which is synthesized in the direction of the replication fork

Ligase

Enzyme that catalyzes the formation of a phosphodiester linkage between the 3’ OH and 5’ phosphate ends of the DNA

Mismatch repair

Type of repair mechanism in which mismatched bases are removed after replication

Mutation

Variation in the nucleotide sequence of a genome

Nitrogenous base

A nitrogen-containing molecule that acts as a base; often referring to one of the purine or pyrimidine components of nucleic acids

Nucleotide excision repair

Type of DNA repair mechanism in which the wrong base, along with a few nucleotides upstream or downstream, are removed

Okazaki fragment

DNA fragment that is synthesized in short stretches on the lagging strand

Phosphate group

A molecular group consisting of a central phosphorous atom bound to four oxygen atoms

Phosphodiester bond

The covalent bond found between two nucleotides

Point mutation

Mutation that affects a single base

Primase

Enzyme that synthesizes the RNA primer; the primer is needed for DNA polymerase to start synthesis of a new DNA strand

Primer

Short stretch of nucleotides that is required to initiate replication; in the case of replication, the primer has RNA nucleotides

Proofreading

Function of DNA polymerase in which it reads the newly added base before adding the next one

Replication fork

Y-shaped structure formed during initiation of replication

Silent mutation

Mutation that is not expressed

Single-strand binding protein

During replication, protein that binds to the single-stranded DNA; this helps in keeping the two strands of DNA apart so that they may serve as templates

Spontaneous mutation

Mutation that takes place in the cells as a result of chemical reactions taking place naturally without exposure to any external agent

Telomerase

Enzyme that contains a catalytic part and an inbuilt RNA template; it functions to maintain telomeres at chromosome ends

Telomere

DNA at the end of linear chromosomes

7-methylguanosine cap

Modification added to the 5’ end of pre-mRNAs to protect mRNA from degradation and assist translation

Alternative RNA splicing

A post-transcription gene regulation mechanism in eukaryotes in which multiple protein products are produced by a single gene through alternative splicing combinations of the RNA transcript

Aminoacyl tRNA synthetase

Enzyme that “charges” tRNA molecules by catalyzing a bond between tRNA and a corresponding amino acid

Anticodon

Three-nucleotide sequence in a tRNA molecule that corresponds to an mRNA codon

Central dogma

States that genes specify the sequence of mRNA, which in turn specify the sequence of proteins

Codon

Three consecutive nucleotides in mRNA that specify the insertion of an amino acid or the release of a polypeptide chain during translation

Colinear

In terms of RNA and protein, three “units” of RNA (nucleotides) specify one “unit” of protein (amino acid) in a consecutive fashion

Degeneracy (of the genetic code)

Describes that a given amino acid can be encoded by more than one nucleotide triplet; the code is degenerate, but not ambiguous

Epigenetic

Describing non-genetic regulatory factors, such as changes in modifications to histone proteins and DNA that control accessibility to genes in chromosomes

Exon

Sequence present in protein-coding mRNA after completion of pre-mRNA splicing

Genetic code

The amino acids that correspond to three-nucleotide codons of mRNA

Hairpin

Structure of RNA when it folds back on itself and forms intramolecular hydrogen bonds between complementary nucleotides

Helicase

An enzyme that helps to open up the DNA helix during DNA replication by breaking the hydrogen bonds

Initiator tRNA

A tRNA that interacts with a start codon, binds directly to the ribosome P site, and links to a special methionine to begin a polypeptide chain

Intron

Non-protein-coding intervening sequences that are spliced from mRNA during processing

Mismatch repair

A form of DNA repair in which non-complementary nucleotides are recognized, excised, and replaces with correct nucleotides

mRNA

Messenger RNA, a form of RNA that carries the nucleotide sequence code for a protein sequence that is translated into a polypeptide sequence

Mutation

A permanent variation in the nucleotide sequence of a genome

Nitrogenous base

A nitrogen-containing molecule that acts as a base; often referring to one of the purine or pyrimidine components of nucleic acids

Nonsense codon/stop codon

One of the three mRNA codons that specifies termination of translation

Nontemplate strand

Strand of DNA that is not used to transcribe mRNA; this strand is identical to the mRNA except that T nucleotides in the DNA are replaced by U nucleotides in the mRNA

Nucleotide excision repair

A form of DNA repair in which the DNA molecule is unwound and separated in the region of the nucleotide damage, the damaged nucleotides are removed and replaced with new nucleotides using the complementary strand, and the DNA strand is resealed and allowed to rejoin its complement

Poly-A tail

Modification added to the 3’ end of pre-mRNAs to protect mRNA from degradation and assist mRNA export from the nucleus

Polysome

mRNA molecule simultaneously being translated by many ribosomes all going in the same direction

Post-transcriptional

Control of gene expression after the FNA molecule has been created but before it is translated into protein

Post-translational

Control of gene expression after a protein has been created

Preinitiation complex

Cluster of transcription factors and other proteins that recruit RNA polymerase II for transcription of a DNA template

Promoter

DNA sequence to which RNA polymerase and associated factors bind and initiate transcription

Reading frame

Sequence of triplet codons in mRNA that specify a particular protein; a ribosome shift of one or two nucleotides in either direction completely abolishes synthesis of that protein

RNA polymerase

An enzyme that synthesizes an RNA strand from a DNA template strand

rRNA

Ribosomal RNA, molecules of RNA that combine to form part of the ribosome

Splicing

Process of removing introns and reconnecting exons in a pre-mRNA

Start codon

AUG (or rarely, GUG) on an mRNA from which translation begins; always specifies methionine

Template strand

Strand of DNA that specifies the complementary mRNA molecule