1. KEY CONCEPT Mutations are changes in DNA that may or may not affect phenotype.
May occur in somatic cells (aren‘t passed to offspring)
May occur in gametes (eggs & sperm) and be passed to offspring
Mutations lead to genetic variation because they randomly change an organisms genetic code.

2. Types of Mutations

3. A gene mutation affects a single gene.
Some mutations affect a single gene, while others affect an entire chromosome.
A gene mutation affects a single gene.
Many kinds of mutations can occur, especially during replication.
Types of Gene Mutations:
A point mutation substitutes one nucleotide for another. Ex: Sickle Cell Anemia
mutated
base

4. Results in a premature stop codon and usually a nonfunctional protein
Nonsense Mutation
Type of point mutation
Results in a premature stop codon and usually a nonfunctional protein

5. A frame-shift mutation inserts or deletes a nucleotide in the DNA sequence. Throws off the reading frame.
THE CAT ATE THE RAT
THC ATA TET HER AT
What would an insertion look like? (draw in notes)

6. Gene Mutation Animation
Draw & explain an inversion mutation.
Skip to silent mutations

7. Chromosomal mutations affect many genes and an entire chromosome
Chromosomal mutations affect many genes and an entire chromosome. Chromosomal mutations may occur during crossing over/meiosis.

8. Crossing over is a normal process (NOT A MUTATION)
Exchange of chromosome segments between homologous chromosomes
Increases genetic diversity
Occurs during Prophase I of Meiosis I
Results in new combinations of genes (chromosomes have a combination of genes from each parent)

9. Chromosome Mutations Five types exist: Deletion Inversion
Translocation
Nondisjunction
Duplication

10. Deletion Due to breakage A piece of a chromosome is lost
Example: cri du chat – chromosome 5

11. Inversion Chromosome segment breaks off Segment flips around backwards
Segment reattaches

12. Translocation results from the exchange of DNA (piece of one chromosome) segments between non-homologous chromosomes. Sometimes chromosomes can fuse onto another chromosome.

13. Nondisjunction Failure of chromosomes to separate during meiosis
Causes gamete to have too many or too few chromosomes (Ex: 3 chromosomes instead of 2 for any given set, or 1 instead of 2)
Examples: Klinefelter’s Syndrome (XXY), Turner Syndrome (X_)

14. Trisomy 21 (Down syndrome)
Nondisjunction
Can cause “Trisomy” (three copies of the same chromosome in an egg or sperm)
Trisomy 21 (Down syndrome)

15. Gene duplication results from unequal exchange of segments crossing over. Results in one chromosome having 2 copies of some genes and the other chromosomes having no copies of those genes.

16. Chromosome Mutation Animation

18. Mutations may or may not affect phenotype.
1. Chromosomal mutations tend to have a big effect.
2. Some gene mutations change phenotype by:
causing a premature stop codon.
causing a change in protein shape or the active site.
causing a change in gene regulation.
blockage
no blockage

19. 3. Some gene mutations do not affect phenotype.
A mutation may be silent because….
It occurs in a non-coding region.
It may not affect protein folding or the active site.

20. Some mutations have no effect and are called “silent”
Silent Mutations
Some mutations have no effect and are called “silent”
Example:
GUC changed to GUG
Both code for the amino acid valine
This would not affect the protein being made in any way

21. Mutations can be caused by several factors.
1. Replication errors can cause mutations.
2. Mutagens, such as UV rays and chemicals, can cause mutations.
3. Some cancer drugs use mutagenic properties to kill cancer cells.
4. Mutations happen regularly
5. Almost all mutations are neutral
6. Many mutations are repaired by enzymes.
7. Some types of skin cancers and leukemia result from somatic mutations
8. Some mutations may improve an organism’s survival (beneficial)

22. Several methods help map human chromosomes.
A karyotype is a picture of all chromosomes in a cell.
X Y

23. Karyotypes can show changes in chromosomes.
deletion of part of a chromosome or loss of a chromosome
large changes in chromosomes
extra chromosomes or duplication of part of a chromosome