Chapter 7 Flashcards
The process of alteration of a gene or chromosome, or the end-product of this process
mutation
mutations can affect genes from one allele (one form of a gene) to another, and thus produce a “mutant” _________
phenotype
A particular DNA sequence that differs by one or more mutations from homologous sequences
Haplotype
have the same sequence or relative position
homologous sequences
Unique genetic makeup of an individual, usually in relation to a specific gene
Genotype
1878-1958 geneticist -one of the first scientists to integrate genetics, development and evolution
Richard Goldschmidt
Proposed new species can arise by mutations (sudden changes in genetic makeup of an organism).
Mutationist Theories
Was the proponent of the idea of a “Hopeful Monster” where a sudden drastic change in the entire genome can sometimes create an entirely new higher taxon (any Linnaean rank above species)
Richard Goldschmidt
Mutationist Theories and Hopeful Monster were refuted by
modern synthesis of biological thought in 1930-1940’s
Even dramatic ________ are limited to alteration of pre-existing traits or developmental pathways.
mutations
“hopeful monster” idea of drastic new mutations is _________ valid
Not
Effects of mutations may be especially minimal in cases of _________ many loci affect the same trait.
polygeny
loci is the plural of _______ which is exact position for a gene on a chromosome
Locus
Are mutations random?
yes
Mutations are random in two areas:
- has no pre-determined “goal”, any nucleotide of the genome can have a mutation
- the environment does not induce advantageous mutations- this is Lamarckian-inheritance of acquired characteristics.
Speciation is driven by
Mutations
1809-1882
Differential survival due to natural selection
Heritable variation
Heritable adaptive variation is due to random mutations.
Charles Darwin
Black moths changed over time because only the ones with the gene to change color would survive being eaten by birds so this is
mutation driven speciation
The average human mutation rate is
0.000000048 per base pair/generation (very low)
A diploid genome has 6.6 x 10^9 bp so the average zygote has ________ new mutations
317
The average human zygote carries about _____mutations that are potentially harmful
7
Mutational event substitution, deletion, or insertion of a base pair
point mutation
chromosomal deletion, insertion, or rearrangement
chromosomal mutation
point mutations result in ______ _____ (changes function of gene) only if they occur in coding region of gene or regulation sequences
gene mutations
occur in somatic cells and only affect the individual in which the mutation arises.
somatic mutations
alter gametes and passed to the next generation
germ-line mutations
what does the acronym G&G stand for?
Germ and Gamete
Which type of mutation occurs at a higher rate?
transition mutations
mutation at one nucleotide-can result in synonymous or silent mutations (no effect on amino acid translation), or non synonymous mutations (change amino acid translation)
base pair substitution
all synonymous and SOME NON SYNONYMOUS mutations can result in NO effect on phenotype or major effects- this is a
neutral mutation
changes an amino acid from one to another in transition mutation
Missense mutation
Changes from an amino acid to a stop codon in a transversion mutation
Nonsense mutation
What are the stop codons?
UAA, UAG, UGA
changes from an amino acid to another amino acid with similar chemical properties; transition mutation
neutral mutation
changes in codon such that the same amino acid is specified in a transition mutation
silent mutation
a type of mussense mutation in that a different amino acid results, but the function of the amino acid doesn’t change
Neutral Mutations
do not result in an amino acid change-remember wobble
silent mutations
a mutation at a different site from original mutation that compensates for the negative effects of the original mutation
suppressor mutation
different chemical states of nitrogenous bases
Tautomers
Normal state of nitrogenous bases.
Keto form
Hydroxyl group (OH) affixed to a carbon with a double bond
Enol Form
Double bond migrates and moves position of hydrogen bonds
Imino Form
These forms are rare-but they can cause unusual base pairing, leading to mutations
Enol and Imino
How do suppressor mutations work?
- mutation in DNA makes a stop codon in mRNA transcript.
- Suppressor mutation in anticodon of tRNA allows it to bind to stop codon.
- Suppressor mutation allow translation to continue, but with one different AA
How do tautomers lead to mutation?
- parental DNA
- DNA replicaiton
- point mutation occurs with wobble
- mismatched base pairs replicate in mRNA
- going back to DNA the base pair is mismatched and it becomes a mutant type DNA.
What types of spontaneous mutations occur without any special anent?
- DNA replication errors
- Base substitution: tautomers→specific transitions.
- Deletions/additions: looping out→ frame shifts in genes.
- Molecular Changes
- Depurination: (1 purine removed): → polymerase stalls at missing base.
- Deanimation (amino group removed from base): C→U, CG→TA transitions.
What type of mutations occur when induced: Radiation & chemicals
- Ionizing and UV light→point mutations+thymine dimers
- Base analogs: high frequency tautomers→specific transitions
- Base modifiers→specific transitions
- intercalators→deletions/additions→frameshift in genes.
- Carcinogens: mutagens that cause cancer
Why does UV light cause mutations?
because DNA absorbs light in the ultraviolet range.
Ultraviolet light commonly causes _______ ______ (T’T) to form , which disrupts A-T pairing, causes a bulge in DNA, disrupts DNA replication at bulge, and can lead to cell death (skin cancer)
Thymine Dimers
Effects of ionizing radiation is ________
cumulative-gets worse over time.
what are Intercalating agents?
agents used to insert or delete a nucleotide in in some template DNA strand.
What is used to stain DNA during electrophoresis
Ethidium bromide
_________ inserts into DNA multiple times, and glows under UV light
Ethidium
what is the result of an addition intercalating agent within a protein coding?
a frame shift mutatioin
what is the result of an intercalating deletion within a protein coding gene?
a new dna strand is replicated and the nucleotide if removed.
removes mutated base and replaces it with the correct one
base-excision repair
Base Excision repair
- Uracil-DNA glycosylase-cleaves bond between sugar and base.
- Endonulease cleavage-cuts away baseless sugar.
- DNA Polymerase activity-inserts correct base.
- ligase activity- bonds new base to others in DNA strand.
In Nucleotide excision repair what can correct thymine dimers and other serious DNA distortions.
proteins
point mutations are divided into two classes :
- forward mutation: changes a wildtype gene to a mutant genel.
- reverse mutation aka reversion or back mutation-changes a mutant gene at the same site so that it functions in a completely wild-type or nearly wild-type way.
the creation of mutations, can occur spontaneously or can be induced.
mutagenesis.
naturally occurring mutations
spontaneous mutation
occur when an organism is exposed either deliberately or accidentally to a physical or chemical agent, known as a mutagen.
induced mutations.
this is the loss of a purine from the DNA when the bond hydrolyzes between the base and deoxyribose sugar, resulting in an apurinic site.
Depurination
This is the removal of an AMINO GROUP from a base.
Deamination
What is considered the “hot spot” for mutations
5 methyl Cytosine
UV light can cause mutations between two pyrimidines which are _______ and will cause them to bond to each other making them ______ ______
thymine, thymine dimers.
1930’s for the discovery of the production of mutations my means of x-ray irradiation
Herman joseph Muller
being able to mutate a gene at specific positions in the base-pair sequence is ______
site-specific mutagenesis
Benzpyrene, a polycyclic aromatic hydrocarbon found in cigarette smoke, coal tar, automobile exhaust fumes, and charbroiled food, is nonmutagenic
but its metabolite, benzpyrene diol epoxide, which is both a mutagen and a carcinogen, can induce cancer.
mutations = what?
DNA damage - DNA repair
There are two general categories of repair systems based on the way they function which are
Direct reversal repair system: which corrects damaged areas by reversing the damage.
2. Excision repair system -which cuts out a damaged area and then repair the gap by new DNA synthesis.
a repair glycosylase enzyme removes the damaged base from the DNA by cleaving the bond between the and the deoxyribose sugar.
base excision repair
Many mismatched base pairs left after DNA replication and missed by proofreading can be corrected by
Methyl-directed mismatch repair
This system recognizes mismatched base pairs, excies the incorrect bases, and then carries out repair synthesis
methyl-directed mismatch repair
what is the last resort for fixing a mutation in the DNA
translesion DNA synthesis
individuals with a lethal affliction to photosensitivity, and portions of their skin have been exposed to light show intense pigmentation, freckling, and warty growths that can become malignant is known as
xeroderma pigmentosum
xeroderma pigmentosum is caused by homozygosity for a recessive mutation ______ ______
repair gene.
which polymerase’s repair DNA in methyl-mismatch repair
DNA polymerase III and ligase
transposable elements fall into two general classes based on how they move from location to location in the genome they are
- found in both prokaryotes and eukaryotes-moves as a DNA segment.
- found only in eukaryotes-are related to retroviruses and move via an RNA. (first an RNA copy of the element is synthesized; then a DNA copy of that RNA is made, and it integrates at a new site in the genome)
who allowed kids with xeroderma pigmentosum into a national park
Walt Disney
Barbara McClintock 1902-1992
Was Born in Hartford CT, an accomplished pianist, and painter and Thomas Henry McClintock a physician was her husband, Went to Cornell Worked with Lowell Randolph, was famous for her work with maize. the corn purple
contains genes for the insertion of the DNA segment into the chromosome and the mobilization of the element to other locations on the chromosome.
transposons
is the simplest transposable element found in bacteria ______
IS (insertion sequence)
The transposition of an IS element requires an enzyme encoded by the IS element called ______
transposase
There are two types of transposons which are
- Composite transposons
2. NonComposite transposons
was awarded the nobel prize in 1983 in physiology or medicine and her discovery of mobile genetics
Barbara McMclintock
worked with corn maize in the 1940’s and 1950’s
Barbara McClintock
Hypothesized the existence of “controlling elements”
Barbara McClintock
TE that functions independently is called
autonomous element
TE that does not function independently but needs help to activate it
non-autonomous element
Both prokaryote and eukaryote have TE’s that encode proteins that allow them to “jump” to another part of the genome or copy and then insert it elsewhere
non-homologous recombinations
Only ______ have a second type of TE that uses reverse transcriptase to make ______ copies of _______ transcripts and insert into the genome.
eukaryotes, DNA, mRNA
TE’s can jump any place randomly into the genome with the following effects:
- if inserted into a coding gene can destroy genes function (null mutation)
- if inserted in a non-coding region (majority) has a neutral effect.
- if inserted into a regulatory region can enhance or destroy it.
- can cause chromosome mutation-inserstion, deletion, or breakage.
why are TE’s in general rare?
because frequent TE activity would likely kill the cell
