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. https://www.youtube.com/watch?v=GieZ3pk9YVo

Types of Mutations

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

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

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)

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

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.

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) http://www.youtube.com/watch?v=5x_Rp1mwotQ

Chromosome Mutations Five types exist: Deletion Inversion Translocation Nondisjunction Duplication

Deletion Due to breakage A piece of a chromosome is lost Example: cri du chat – chromosome 5 http://www.youtube.com/watch?v=hJcPr3MyBww http://learn.genetics.utah.edu/content/chromosomes/diagnose/

Inversion Chromosome segment breaks off Segment flips around backwards Segment reattaches

Translocation results from the exchange of DNA (piece of one chromosome) segments between non-homologous chromosomes. Sometimes chromosomes can fuse onto another chromosome. http://learn.genetics.utah.edu/content/chromosomes/diagnose/

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_)

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

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.

Chromosome Mutation Animation

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

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.

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

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)

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

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