{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Lecture.20.Fall.2013 - Mutation and DNA repair November 6...

Info icon This preview shows pages 1–13. Sign up to view the full content.

View Full Document Right Arrow Icon
Mutation and DNA repair November 6, 2013 Gene Mutations (Chapter 18) Categories of mutations Phenotypic effects of mutations Suppressor mutations Intragenic vs. intergenic suppression Mutations result from internal and external factors. spontaneous mutations
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Mutation and DNA repair November 6, 2013 Mutations result from internal and external factors. induced mutations Chemically induced mutations Radiation-induced mutations Radiation exposure in humans DNA repair Mismatch repair
Image of page 2
Expanding trinucleotide repeats Mutations in which the number of copies of a trinucleotide ( a set of three nucleotides) increases in number are called expanding trinucleotide repeats . First observed in 1991 in a gene called FMR-1 Mutation of FMR-1 causes Fragile-X Syndrome, the most common hereditary cause of metal retardation.
Image of page 3

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Expanding trinucleotide repeats Normal FMR-1 allele has < 60 copies of the trinucleotide repeat CGG. In people with fragile-X syndrome, the FMR-1 allele may have hundreds or even thousands of copies. Why might this matter?
Image of page 4
Expanding trinucleotide repeats
Image of page 5

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Trinucleotide expansion during replication
Image of page 6
Loss-of-function and Gain-of-function mutations Loss-of-function mutations cause the complete or partial absence of normal protein function. Alters the structure of the protein so that it no longer works correctly. Frequently caused by early nonsense mutations, which truncate the protein. Can also result from mutations in regulatory regions that affect transcription, translation, or splicing of the protein.
Image of page 7

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Loss-of-function mutations Frequently recessive , so that an individual diploid organism must be homozygous to exhibit the mutant phenotype. Hypomorphic: mutations that reduce but do not eliminate gene function “Null” or “complete loss of function”: mutations that completely eliminate gene function “Haploinsufficient” - null mutations that are dominant, due to a requirement for two copies of the mutated gene
Image of page 8
Loss-of-function and Gain-of-function mutations Gain-of-function mutations: result in a new function, or cause gene expression in an inappropriate tissue or at an inappropriate time in development or under inappropriate cellular conditions.
Image of page 9

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Gain-of-function mutations Example: a mutation might occur in a gene that encodes a receptor for a growth factor that changes the protein such that it is active in the absence of the growth factor Would stimulate growth/cell division regardless of conditions = dominant
Image of page 10
Loss-of-function and Gain-of-function mutations Gain-of-function mutations e.g. 2: The lac superrepressor mutation Usually dominant , as the protein is now doing something it did not previously do.
Image of page 11

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Other types of mutations Dominant negative: mutant protein interferes with the function of the wild type protein, leading to a dominant loss-of-function phenotype • Regulatory: disrupts the regulation of a gene’s expression (promoter or enhancers) – May be lof or gof mutations, dominant or recessive
Image of page 12
Image of page 13
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern