Genetics

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Mutation

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hertible changes in base sequence that affect phenotype

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A forward mutation

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a mutation that changes a wild type allele of a gene to a different allele

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Reverse mutation or reversion

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mutation that can turn a novel mutant allele back to a wild type

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Transition mutation

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is a type of substitution (mutation occrs when a base at a certain position in one strand of the dna molecule is replaced by one of the other three bases) which ibe ourine replaces another purine or pyrimidine replacecs a pyrimidine

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Transversion mutation

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a mutation in which in which a purine changes into a pyrmaidine

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Deletion mutation

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occurs when a block of one or more nucleotide pairs is lost from a DNA molecule

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Insertion

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is the addition of one or more nucleotide pairs

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Inversions

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are 180 degree rotationas of segments of DNA molecule

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Reciprocal translocations

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parts of two non homologous chromosomes change places

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Depurination

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the hydrolysis of a purine base a or g from the deoxyribose phosphate backbone

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deaminoation

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is the removal of an amino NH2 group that may modify DNA's information this can sometime change cytosine to uracil

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un equal crossing over

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two closely related DNA sequences located in different places on two homologous chromosomes can pair with each other during meiosis
Figure 5.5 Unequal crossing over generates gene families. The left side illustrates an unequal crossing over event and the two products that are generated. One product is deleted and the other is duplicated for the same region. In this example, the duplicated region contains a second complete copy of a single gene (B). The right side illustrates a second round of unequal crossing over that can occur in a genome that is homozygous of the original duplicated chromosome. In this case, the crossover event has occurred between the two copies of the original gene. Only the duplicated product generated by this event is shown. Over time, the three copies of the B gene can diverge into three distinct functional units (B1, B2, and B3) of a gene family cluster.

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Transposable elements TES

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are DNA segements several hundred to several thousand base pairs long that move or (Transpose or jump) from place to plave in the genome

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Mutagen

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any physical or chemical agent that raises the frequency of mutations above the spontaneous rate

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Base analogs

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they are so similar in chemical structure to the normal nitrogenous bases that the replication machinery can incorporate them into DNA in place of nitrogenous bases since a base analog can have pairing properties different from those of the baseit replaces it can cause base substitutions on the complementary strand synthesized in the next round of dna replication

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Intercalators

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flat planar molecules that can sandwich themselves between successive base pairs and disrupt the machinery for replication recombination and repair

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Homology dependent repair

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a general strategy where a repair system will first cut out the small region of the dna strand that contains the the altered nucleotidw and then use the other strand to act as a template to resynthesize the region types include Base excision repair and nuclotide excision repair

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nonhomologous end joining

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mechanism for stitching back together ends formed by double strand breaks it relies on proteins that bind to the end of the broken DNA strands and bring them close together overhanging ends are often trimmed during non homologous end joining resulting in deletion

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Point mutation

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a mutation of one base pair

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Cistron

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a term used as a synonoym for complementation group or gene

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Hot spots

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sites within a gene that mutate more frequently than others either spontaneously or after treatment with a particular mutagen

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Pleiotropy

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phenonmenon in which a single gene determines a number of distinct and seemingly unrealted characteristics

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Alkaptonuria

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Alkaptonuria is an inherited condition that causes urine to turn black when exposed to air. Ochronosis, a buildup of dark pigment in connective tissues such as cartilage and skin, is also characteristic of the disorder. This blue-black pigmentation usually appears after age 30. People with alkaptonuria typically develop arthritis, particularly in the spine and large joints, beginning in early adulthood. Other features of this condition can include heart problems, kidney stones, and prostate stones.

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Auxotroph

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a mutant microorganism that can grow on minimal medium only if it has been supplemented with one or motr growth factors not required by wild type strains

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Peptide bond

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a covalent bond that joins amino acids during protein synthesis

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Lysis

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(Greek λύσις, lysis from lyein = to separate) refers to the death of a cell by breaking of the cellular membrane, often by viral or osmotic mechanisms that compromise its integrity.[citation needed] A solution containing the contents of lysed cells is called a "lysate".

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Complementation

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process in which hetereozygosity for chromosomes bearing mutant recessive alleles for two different genes produces a normal phenotype

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Base excision repair

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1) DNA Glycosylase remove wrong base leaving an AP site
2)Enzyme AP endonuclease makes a nick in DNA backbone at AP site
3)DNA exonuclease attack the nick and remove nucleotides from its vicinity to create a gap
4) DNA polymerase fills in the gap
5) DNA ligase seals up the backbone

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Nuclear Excision repair

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involved in the removal of a variety of bulky DNA lesions such as UV induced cyclobutane pyrimidine dimers (CPD) and pyrimidine 6-4 pyrimidone photoproducts (6-4PP).
(i) recognition of a DNA lesion;
(ii) separation of the double helix at the DNA lesion site;
(iii) single strand incision at both sides of the lesion;
(iv) excision of the lesion-containing single stranded DNA fragment;
(v) DNA repair synthesis to replace the gap and
(vi) ligation of the remaining single stranded nick

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Enzymes that repair

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1) Alkyltransferase- enzymes that can remove added methyl or ethyl groups from guanine
2) photolyase- recognize thimine dimers but is a photorepair

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Mismatch repair

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Mismatch repair deals with correcting mismatches of the normal bases; that is, failures to maintain normal Watson-Crick base pairing (A•T, C•G)
It can enlist the aid of enzymes involved in both base-excision repair (BER) and nucleotide-excision repair (NER) as well as using enzymes specialized for this function.

Recognition of a mismatch requires several different proteins including one encoded by MSH2.
Cutting the mismatch out also requires several proteins, including one encoded by MLH1.
Mutations in either of these genes predisposes the person to an inherited form of colon cancer. So these genes qualify as tumor suppressor genes.

Question: How does the MMR system know which is the incorrect nucleotide? In E. coli, certain adenines become methylated shortly after the new strand of DNA has been synthesized. The MMR system works more rapidly, and if it detects a mismatch, it assumes that the nucleotide on the already-methylated (parental) strand is the correct one and removes the nucleotide on the freshly-synthesized daughter strand. How such recognition occurs in mammals is not yet known.