Exam 4 Terms

Law of Segregation

The two alleles for each gene separate

Law of Independent Assortment

Alleles of genes on nonhomologous chromosomes assort independently

Mutant phenotypes

traits alternative to the wild type

Sex-linked gene

gene located on either sex chromosome

Linked genes

genes that are close to each other on a chromosome and are more likely than others to be inherited together

mechanism

crossing over

parental types

offspring with a phenotype matching one of the parental phenotypes

recombinant types

offspring with nonparental phenotypes (new combinations of traits)

genetic recombination

the production of offspring with combinations of traits differing from either parent

crossing over

the reciprocal exchange of genetic material between non-sister chromatids during prophase I of meiosis

genetic map

an ordered list of the genetic loci along a particular chromosome

linkage map

genetic map of a chromosome based on recombination frequencies

cytogenetic maps

indicate the positions of genes with respect to chromosomal features

nondisjunction

pairs of homologous chromosomes do not separate normally during meiosis I or sister chromatids do not separate during meiosis II

aneuploidy

results from fertilization involving gametes in which nondisjunction occurred

monosomic zygote

has only one copy of a particular chromosome

trisomic zygote

three copies of a particular chromosome

polyploidy

condition in which an organism has more than two complete sets of chromosomes

triploidy (3n)

three sets of chromosomes

tetraploidy (4n)

four sets of chromosomes

deletion

removes a chromosomal segment

duplication (harmful)

repeats a segment

inversion

reverses orientation of a segment within a chromosome

translocation (harmful)

moves a segment from one chromosome to another

transformation

change in genotype and phenotype due to assimilation of foreign DNA

virus

DNA or RNA enclosed by a protective coat, usually made of protein

Chargaff’s rules

1. base composition of DNA varies between species


1. in any species the percentages of A and T bases are equal and the percentages of G and C bases are equl

antiparallel

subunits run in opposite directions

DNA replication

the __parent__ molecule unwinds and two new __daughter__ strands are built based on base-pairing rules

Origins of replication

replication begins here

two DNA strands are separated, opening up a replication “bubble

Replication fork

located at the end of a bubble

helicases

enzymes that untwist the double helix at the replication forks

single-strand binding proteins

bind to and stabilize single-stranded DNA

Topoisomerase

relieves the strain caused by tight twisting ahead of the replication fork by breaking, swiveling, and rejoining DNA strands

Short RNA primer

the initial nucleotide strand

DNA polymerases

enzymes catalyze the elongation of new DNA at a replication fork

* they add nucleotides to the 3’ end of a preexisting chain

leading strand

toward the replication fork

lagging strand

away form the replication fork

Okazaki fragments

DNA ligase

the remaining gaps are joined together by

chromatin

a complex of DNA and protein, is found in the nucleus of eukaryotic cells

histones

proteins responsible for the first level of DNA packing in chromatin

nucleosome

consists of DNA wound twice around a protein core of eight histones, two of each of the main histone types

plasmids

small circular DNA molecules that replicate separately from the bacterial chromosome

gene cloning

production of multiple copies of a single gene

cloning vector

plasmid that carries the cloned DNA

Taq polymerase

* key to PCR
* heat-stable DNA polymerase

DNA sequencing

once a gene is cloned, complementary base pairing can by exploited to determine the gene’s complete nucleotide sequence

proteins

link between genotype and phenotype

ribsomes

sites of translation

transcription happens

in the nucleus

translation happens

in the cytoplasm

Translation happens after

transcription is completed

Transcription is the

DNA-Directed Synthesis of DNA

RNA polymerase

enzyme the pries the DNA strands apart and joins together the complementary RNA nucleotides

In bacteria

the polymerase stops transcription at the end of the terminator and mRNA can be translated without further modification

In eukaryotes

RNA polymerase II transcribes the polyadenylation signal sequence, the RNA transcription is released 10-35 nucleotides past this polyadenylation sequence

RNA splicing

remove the introns and keep the exons

introns

noncoding regions

exons

usually translated into amino acid sequences

spliceosomes

RNA splicing is carried out by

wobble

flexible pairing at the third base of a codon

the P site

holds the tRNA the carries the growing polypeptide chain

the A site

holds the tRNA that carries the next amino acid to be added to the chain

the E site

is the exit site, where discharged tRNAs leave the ribosome

release factor

causes the addition of a water molecule instead of an amino acid

polyribosomes

string of ribosomes

in bacteria, the transcription and translation

can take place simultaneously

in eukaryotes, what separates transcription and translation

the nuclear envelope

mutations

changes in the genetic material of a cell

point mutations

are chemical changes in just one nucleotide pair of a gene

nucleotide-pair substitution

replaces one nucleotide and its partner with another pair of nucleotides

silent mutations

have no effect on the amino acid produced by a codon because of redundancy in the genetic code

missense mutations (most common)

change one amino acid to another

nonsense mutations

change an amino acid codon into a stop codon, leading to a nonfunctional protein

frameshift mutation

produced by insertion or deletion of nucleotides that may alter the reading frame of genetic message

mutagens

physical or chemical agents that can cause mutations

natural selection has favored

bacteria that produce only the gene products needed by the cell

The operon model

gene expression in bacteria is controlled by a mechanism

operon

is the entire stretch of DNA that \n includes the operator, the promoter, and the \n genes that they control

operator

the regulatory “on-off switch” of the genes, segment of DNA

corepressor

molecule that cooperates with a repressor protein to switch an operon off

inducer (allotactase)

inactivates the repressor to turn the lac operon on

repressible enzymes

usually function in anabolic pathways; their synthesis is repressed by high levels of the end product

inducible enzymes

usually function in catabolic pathways; their synthesis is induced by a chemical signal

activated CRP

attaches to the promoter of the lac operon and increases the affinity of RNA polymerase, thus accelerating transcription

cell types are organized into…

tissues, organs, organ systems, and the whole organism

Bacteriophages

viruses that infect bacteria

semiconservative model

predicts that when a double helix replicates, each daughter molecule will have one old strand and one newly made strand

Primase

enzyme that starts an RNA chain with a single RNA nucleotide and adds RNA nucleotides one at a time

nucleic acid hybridization

the base pairing of one strand of a nucleic acid to another, complementary sequence

genetic engineering

the direct manipulation of genes for practical purposes

restriction enzymes

cut DNA molecules at specific DNA sequences (restriction sites)

sticky ends

can bond with complementary sticky ends of other fragments

gel electrophoresis

cutting DNA molecules with restriction enzymes to see fragments

nanopore methods

moving a single DNA strand through a tiny pore in a membrane

CRISPR-Cas9 System

1. guide molecule matches the target gene to be slices
2. DNA sequences are introduced to target cells and the enzyme cutes the DNA there
3. RNA leads Cas9 to the desired location and the enzyme cuts
4. Sequence can be inserted that repairs, alters, the host cell’s DNA

In the early 20th century what were the best candidates for the genetic material for inheritance?

DNA and Protein

Research of Frederick Griffith in 1928

* worked with two strains of bacterium, one pathogenic and one harmless
* killed pathogenic cells = living cells became patho
* “tranformation” - even if virus killed, will still infect

Hershey and Chase research 1952

* DNA is genetic material of a phage known as T2
* phage provides the genetic information