Genetic Change

I. Review

• The Genetic Code

• What is a Gene?

-protein (may have more than 1 polypeptide chain)

-rRNA

-tRNA

-introns

II. Mutation

A. Definition-change in sequence or number of nucleotides in DNA

-somatic; sex cells

-source of variation for natural selection (species diversity)

B. Types of Mutations

1. point mutations

• substitutions (missense and nonsense)
• deletions (frameshift)
• example: hemoglobin S (missense mutation) & sickle cell anemia

2. transposons

• discovered by Barbara McClintock (Nobel Prize 1983)
• move as DNA
• "Jumping Genes" in Corn mechanism

from: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/Transposons1.gif

3. chromosomal mutations

• chromosomal breakage
• chromosomal fusion

C. The Causes of Mutations

1. What are mutagens? -agents that increase natural rate of mutation

2. Types of Mutagens: Radiation

a. ionizing radiation

-x-rays, gamma rays

-electrons in atom absorb energy as ionizing radiation passes through matter causing free radicals

-Ionizing Radiation; Free Radicals

-Free radicals can cause base damage, DNA strand breaks

-Damage is typically repaired/sometimes mistakes are made leading to mutation

b. UV radiation

-lower energy

-component of sunlight

-no free radicals

-only certain molecules absorb UV

-effects of UV:

-thymine dimers

-photolyase

• Xeroderma pigmentosum treatment

from: http://www.zdf.de/ZDFde/img/7/0,1886,2396551,00.jpg

3. Types of Mutagens: Chemicals

• What do chemical mutagens look like?

-Base modifiers (alters pairing properties of bases)

-Intercalating agents (inserts between bases of DNA causing a frameshift)

• The Ames Test

from: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/AmesTest.html

4. Mutation and Cancer