The number of events that produce mutated alleles per locus per generation.
If 4 of 100,000 births show a mutation from a recessive to a dominant allele, we've ctually sampled 200,000 genes because we have two copies of each gene. So the mutation rate would be 4/200,000 or 2/100,000.
To ensure that the mutant phenotype can be measured, it must:
Never be produced by recessie alleles
Always be fully expressed and completely penetrant so that mutant individuals can be indentified
Have clearly established paternity
Never be produced by nongeneric agents such as drus or infection and be produced by a dominantly inherited mutation of only one gene
Focused on environmental causes of mutations
Ames and his test
Identified mutagenic agents but the disadvantage to this test was that he used bacteria, which is a different metabolic pathway than is found in rats or humans. Sonce the bacteria doesn't have that metabolic product, just abecause a chemical passes the Ames test, doesn't necessarily mean that it is not a mutanogen
Mutations that cause the substitution of one amino acied for another in a protein.
Mutations that change a termination codon into one that codes for an amino acid. Such mutations produce elongated protiens.
UAA-->AAA (removal of termination codon
Mutations that change an amino acid specifying a codon to one of the three termination codons. This shortens the protein product.
AAA-->UAA (termination codon)
Mutational events in which a number of bases (other than multiples of three) are added to or removed from DNA, causing a shift in the codon reading frame.
Insertion: CAT CAT CAT GCA T
Deletion: CAT CAT CAC AT
A form of mutation associated with the expansion in copy number of a nucleotide triplet in or near a gene
How many trinucleotide repeats are there in Fragile X syndrome?
CGC - 230
How many trinucleotide repeats are there in Myotonic Dystrophy?
CTG - 50 to 2,000 repeats
How many trinucleotide repeats are there in Huntington's Disease?
CAG - 42 to 100
Onset of a generic disorder at earlier ages and with increasing severity in successive generations
Examples of DNA repair genes
UV damage - thymine dimers (excision repair)
Xeroderma Pigmentosum - thymine dimer defect
Bloom Syndrome - DNA ligase defect
Genomic Imprinting: Reversible alterations to the genome
Activate certain genes and deactivate other genes. Sometimes, genes that are not necessary are activated and start influencing changes. This results in chance for mutations and an increase in the chance for cancer.
Fetal tissue mutations
A cell when it has the ability to give rise to an entire organism. Occurs during the 16 cell stage.
Genetically identical molecules, cells, or organisms all derived from a single ancestor.
Reproductive cloning and therapeutic cloning
The two types of stem cell cloning
Why stem cell clones are not exact replicas
1. telomeres of chromosomes of donor nuclei are shorter
2. genomic imprinting when chromosomes are passed via germ line
3. somatic cells accumulate mutations
4. X-inactivation pattern
5. mitochondria is from recipient cell not donor cell
6. coat color differences-pigmented cells move about differently
7. environmental factors during embryonic/fetal development: nutrition (methylation) stress, exposure to environmental diseases
Why stem cell cloning fails
1. Meiosis not involved (meiosis in the female completes fertilization)
2. Diploid nucleus is plunked into oocyte cytoplasm where signals direct it to do what a female secondary oocyte tends to do (a.) shed half of chromosomes as polar body--hapoid--lethal and (b.) replicates DNA--tetraploid--lethal
Bioethical issues of stem cell cloning
1. Violation of rights of early-stage embryos versus violation of rights of individuals who might benefit from such therapy
2. 2001 USA legislation outlaw creating or selling "any embryo produced by human cloning"
Steps of cloning genes
1. isolate plasmid DNA and human DNA
2. cut both DNA's with the same restriction endonuclease--resulting in DNA fragments
3. combine both DNA's--cut ends re-associate or anneal
4. seal gaps with DNA ligase
5. creates recombinant DNA molecules composed of human DNA and vector DNA
6. transfer vector into bacteria
7. at each bacterial cell division, the plasmid is replicated resulting in many copies or clones of the DNA insert
8. lyse bacteria--extract recombinant plasmids
9. cloned human DNA can be released from plasmid with same restriction enzyme used for cloning
10. cloned DNA can be used directly, put in expression vector and transfected into cells
Human genomic library
1. A collection of clones that contain all of the genetic information in an individual--cut all DNA of donor cell--put in cloning vector (bacteriophage as an example)
2. Retrieve gene of interest ("needle in hay stack") by using DNA probe
3. DNA probe--a synthetic piece of labeled DNA that is complementary to part of gene of interest
Extract mRNA from cells, reverse transcribe to single stranded cDNA. DNA polymerase to give double-stranded cDNA, cut, put in cloning vector
Polymerase Chain Reaction (PCR)--1986
A method for amplifying DNA segments using cycles of denaturation, annealing to primers, and DNA-polymerase-directed DNA synthesis.
1. DNA amplified by heating to break hydrogen bonds, yielding single strnded DNA
2. Short nucleotide sequences act as primers for DNA replication added
3. Enzyme, DNA polymerase, begins t primers and synthesizes a DNA strand complementary to the region between the primers, a proces called "primer extension"