1. Mutations

2. What is a Mutation? A mutation is a change in an organism’s DNA
May or may not affect the phenotype

3. Types of Mutations Gene Mutations Chromosomal Mutations Point mutation
Frameshift mutation
Chromosomal Mutations
Gene duplication
Translocation
Nondisjunction

4. Gene Mutations Point Mutation Frameshift Mutation
One nucleotide is substituted for another during DNA replication
Also called substitution
Ex: GCGAT changed to GCGTT
Nonsense (early stop codon), missense (changes the amino acid produced), or silent (no effect on phenotype)
Frameshift Mutation
A nucleotide is inserted or deleted
Shift the entire sequence of codons
Also called insertion or deletion

5. Frameshift Mutation Imagine a sentence of three-letter “codons”
Remember the process of translation?
THE CAT ATE THE RAT
If the letter E is deleted from the first “THE,” all the letters that follow shift to the left. The sentence now reads:
THC ATA TET HER AT…
Think about the effect this would have on the protein built during translation.
Which mutation is worse: point or frameshift? Why?

6. Chromosomal Mutations
Gene duplication
During crossing over in prophase I, homologous chromosomes may not be properly aligned
When they exchange pieces of DNA, these segments could be different sizes
One chromosome could have two copies of a gene while the other has none

7. Chromosomal Mutations
Translocation
Nonhomologous chromosomes exchange segments of DNA
Like crossing over, but this is not a good thing!

8. Chromosomal Mutations
Nondisjunction
Chromosomes do not separate after crossing over
Results in offspring that are missing or have extra chromosomes
“Trisomy”
Ex: Down’s Syndrome

9. Genetic Disorders We can use karyotypes to diagnose genetic disorders
The most common example is Down’s Syndrome
Caused by having three copies of the 21st chromosome
Also known as Trisomy 21

10. Chromosomal Mutations
Trisomies
Down’s Syndrome (trisomy 21)
Edward’s Syndrome (trisomy 18)
Strong physical defects
Patau Syndrome (trisomy 13)
polydactly
Sex Chromosomes
Turner’s Syndrome (XO)
Short stature, undeveloped bodies, infertility
Klinefelter’s Syndrome (XXY)
Tall, decreased testosterone, infertility
XYY Syndrome
Low effect on phenotype
Tall, sometimes reduced IQ

11. Impact of Mutations
Chromosomal mutations affect many genes, so have a bigger impact on an organism than single gene mutations
Gene mutations may or may not have an effect
Frameshift mutations are worse
Point mutations may not effect the amino acid sequence at all
Mutations in body cells affect only the individual, while mutations in germ cells, or gametes, will also be passed on to offspring

12. Causes of Mutations Replication errors
Mutagens: environmental causes of DNA mutation
These include UV rays and chemicals

13. Cancer
Cancer occurs when cells are mutated so that they grow uncontrollably
They do not follow the normal cell cycle pattern of growth and division
Carcinogens: factors known to cause cancer