Bio exam 3

Allele

one of two or more variants of a gene that determines a particular trait for a characteristic

Continuous variation

a variation in a characteristic in which individuals show a range of traits with small differences between them

Discontinuous variation

Variation in a characteristic in which individuals show two, or a few, traits with large differences between them

Epistasis

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

Hybridization

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

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

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

Linkage

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

Model system

a species or biological system used to study a specific biological phenomenon to gain understanding that will be applied to other species

Mono hybrid

a cross of two individuals for a single contrasting trait

Recombination

the process during meiosis in which homologous chromosomes exchange linear segments of genetic material, thereby dramatically increasing genetic variation in the offspring and separating linked genes

Test cross

a cross between a dominant expressing individual with an unknown genotype and a homozygous recessive individual; the offspring phenotypes indicate whether the unknown parent is heterozygous or homozygous for the dominant trait

Wild type

the most commonly occurring genotype or phenotype for a given characteristic found in a population

X-Linked

a gene present on the X chromosome, but not the Y chromosome

alternative RNA splicing

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

Codon

three consecutive nucleotides in mRNA that specify the addition of a specific amino acid or the release of a polypeptide chain during translation

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

Epigenetic

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

Exon

a sequence present in protein-coding mRNA after completion of pre-mRNA splicing

Gene expression

Processes that control whether a gene is expressed

Genetic code

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

Helicase

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

Intron

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

Lagging strand

during replication of the 3' to 5' strand, the strand that is replicated in short fragments and away from the replication fork

Leading strand

the strand that is synthesized continuously in the 5' to 3' direction that is synthesized in the direction of the replication fork

Mismatch repair

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

mRNA

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

nontemplate strand

the 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

Okazaki fragments

the DNA fragments that are synthesized in short stretches on the lagging strand

Phosphate group

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

Post transcriptional

control of gene expression after a protein has been created

Primer

a short stretch of RNA nucleotides that is required to initiate replication and allow DNA polymerase to bind and begin replication

Promoter

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

Replication form

The Y-shaped structure formed during the initiation of replication

RNA polymerase

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

rRNA

molecules of RNA that combine to form part of the ribosome

semiconservative replication

The method used to replicate DNA in which the double stranded molecule is separated and each strand acts as a template for a new strand to be synthesized, so the resulting DNA molecules are composed of one new strand of nucleotides and one old stand of nucleotides

Splicing

the process of removing introns and reconnecting exons in a pre-mRNA

Stop codon

One of the three mRNA codons specifies termination of translation

Telomerase

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

Telomere

The DNA at the end of linear chromosomes

Template strand

The strand of DNA that specifies the complementary mRNA molecule

Transcription bubble

The region of locally unwound DNA that allows transcription of mRNA.

tRNA

an RNA molecule that contains a specific three-nucleotide anticodon sequence to pair with the mRNA codon and also binds to a specific amino acid