Biology 151 Exam 3

allele

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

autosomes

any of the non-sex chromosomes

blending theory of inheritance

hypothetical inheritance pattern in which parental traits are blended together in the offspring to produce and intermediate physical appearance

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

dominant lethal

inheritance pattern in which an allele is lethal both in the homozygote and the heterozygote; this allele can only be transmitted if the lethality phenotype occurs after reproductive age

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; 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 chromosome

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 dominance

in a heterozygote, one trait will conceal the presence of another trait for the same characteristic

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 (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

model system

species or biological system used to study a specific biological phenomenon to be applied to other different species

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

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 carried a dominant trait for that same characteristic; when present as two identical copies, the recessive trait is expressed

recessive lethal

inheritance pattern in which an allele is only lethal in the homozygous form; the heterozygote may be normal or have some altered, nonlethal phenotype

reciprocal cross

paired cross in which the respective traits of the male and female in one cross become the respective traits of the female and male in the other cross

sex-linked

any gene on a sex chromosome

sum rule

probability of the occurrence of at least one of two mutually exclusive events is the sum of their individual probabilities

test cross

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

trait

variation in the physical appearance of a heritable characteristic

x-linked

gene present on the X, but not the Y chromosome

Mendel

the scientist who used garden peas to study inheritance

melanocyte

pigment cell in our skin, present in all parts of our bodies

eumelanin

produces brown-black pigment, synthesized in the golgi apparatus

phiomelanin

produces red-yellow pigment, synthesized in the golgi apparatus

electrophoresis

technique used to separate DNA fragments according to size

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

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

ligase

enzyme that catalyses 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

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

point mutation

mutation that affects a single base

primase

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

primer

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

proofreading

function of DNA pol 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

sliding clamp

ring-shaped protein that holds the DNA pol on the DNA strand

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

topoisomerase

enzyme that prevents overwinding of DNA when DNA replication is taking place

transformation

process in which external DNA is taken up by a cell, thereby changing its morphology and physiology

transition substitution

when a purine is replaced with a purine or a pyrimidine is replaced with another pyrimidine

transversion substitution

when a purine is replaced by a pyrimidine or a pyrimidine is replaced by a purine

Friedrich Miescher

discovered nucleic acids

Frederick Griffith

reported the first demonstration of bacterial transformation, worked with Streptococcus Pneumoniae (rough and smooth)

r strain

non-pathogenic, involved with mice and Frederick Griffith

s strain

pathogenic, involved with mice and Frederick Griffith

Hershey and Chase

provided confirmatory evidence that DNA was indeed the genetic material (not proteins); studied bacteriophages

Erwin Chargaff

examined the content of DNA in different species and found that the amounts of adenine, thymine, guanine, and cytosine were not found in equal quantities in different species

nucleotides

the building blocks of DNA, consist of a phosphate group, a nitrogenous base, and a pentose sugar

7-methylguanosine cap

modification added to the 5' end of pre-mRNA from degradation and assist translation

aminoacyl tRNA synthetase

enzyme that "charges" the tRNA molecules by catalyzing a bond between the tRNA and a corresponding amino acid

anticodon

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

CAAT box

essential eukaryotic promoter sequence involved in binding transcription factors (GGCCAATCT)

central dogma

states that genes specify the sequence of mRNAs, 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

consensus

DNA sequence that is used by many species to perform the same or similar functions

core enzyme

prokaryotic RNA polymerase consisting of α, α, β, and β', but missing σ; this complex performs elongation

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

downstream

nucleotides following the initiation site in the direction of mRNA transcription; in general, sequences that are toward the 3' end relative to a site on the mRNA

exon

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

FACT

complex that "facilitates chromatin transcription" by disassembling nucleosomes ahead of a transcribing RNA polymerase II and reassembling them after the polymerase passes by

GC-rich box

(GGCG) nonessential eukaryotic promoter sequence that binds cellular factors to increase the efficiency of transcription; may be present several times in a promoter

hairpin

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

holoenzyme

prokaryotic RNA polymerase consisting of α, α, β, β', and σ; this complex is responsible for transcription initiation

initiation site

nucleotide from which mRNA synthesis proceeds in the 5' to 3' direction; denoted with a "+1"

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 the mRNA during processing

Kozak's Rules

determines the correct initiation AUG in a eukaryotic mRNA; the following consensus sequence must appear around the AUG: 5'-GCC(purine)CCAUGG-3'

nonsense 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 with U nucleotides in the mRNA

Octamer box

(ATTGCAT) nonessential eukaryotic promoter sequence that binds cellular factors to increase the efficiency of transcription; may be present several times in a promoter

peptidyl transferase

RNA-based enzyme that is integrated into the 50S ribosomal subunit and catalyzes the formation of peptide bonds

plasmid

extrachromosomal, covalently closed, circular DNA molecule that may only contain one or a few genes; common in prokaryotes

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

preinitiation complex

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