Turner College & Career High School  2016 Mutations Turner College & Career High School  2016

What Are Mutations? Changes in the nucleotide sequence of DNA. May occur in somatic cells (body, not egg or sperm) and are not usually passed to offspring. May occur in gametes (eggs & sperm) and be passed to offspring.

Are Mutations Helpful or Harmful? Mutations happen regularly. Almost all mutations are neutral. Chemicals & UV radiation cause mutations. Many mutations are repaired by enzymes.

Are Mutations Helpful or Harmful? Some type of skin cancers and leukemia result from somatic mutations. Some mutations may improve an organism’s survival (beneficial)

2 Types of Mutations

1 Chromosome Mutations Caused by variations in: The structure of a chromosome. The loss or gain of part of a chromosome. The number of chromosomes.

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

1 Duplication Occurs when a gene sequence is repeated.

1 Translocation Involves two chromosomes that aren’t homologous. Part of one chromosome is transferred to another chromosome.

1 Nondisjunction Failure of chromosomes to separate during meiosis. Causes gamete to have too many or too few chromosomes. Some Disorders: Down Syndrome: three 21st chromosomes. Turner Syndrome: single X chromosome.

Gene Mutations

2 Gene Mutations Change in the nucleotide sequence of a gene. May only involve a single nucleotide. May be due to copying errors, chemicals, viruses, etc.

2 Mutation Types Missense Nonsense Insertion Deletion Duplication Frameshift Repeat Expansion

2 Missense Mutation This type of mutation is a change in one DNA base pair that results in the substitution of one amino acid for another in the protein made by a gene.

2 Missense Mutation Sickle Cell disease is the result of one nucleotide substitution. Occurs in the hemoglobin gene.

2 Nonsense Mutation A nonsense mutation is also a change in one DNA base pair. Instead of substituting one amino acid for another, however, the altered DNA sequence prematurely signals the cell to stop building a protein. This type of mutation results in a shortened protein that may function improperly or not at all.

2 Nonsense Mutation

2 Insertion An insertion changes the number of DNA bases in a gene by adding a piece of DNA. As a result, the protein made by the gene may not function properly.

2 Deletion A deletion changes the number of DNA bases by removing a piece of DNA. Small deletions may remove one or a few base pairs within a gene, while larger deletions can remove an entire gene or several neighboring genes. The deleted DNA may alter the function of the resulting protein(s).

2 Deletion

2 Duplication A duplication consists of a piece of DNA that is abnormally copied one or more times. This type of mutation may alter the function of the resulting protein.

2 Frameshift Mutation This type of mutation occurs when the addition or loss of DNA bases changes a gene's reading frame. A reading frame consists of groups of 3 bases that each code for one amino acid. A frameshift mutation shifts the grouping of these bases and changes the code for amino acids. The resulting protein is usually nonfunctional. Insertions, deletions, and duplications can all be frameshift mutations.

2 Frameshift Mutation

2 Frameshift Mutation Inserting or deleting one or more nucleotides. Changes the “reading frame” like changing a sentence. Proteins built incorrectly. Original: The fat cat ate the wee rat. Frame Shift (“a” inserted): The fat caa tat eth ewe era t. Frame Shift (“a” deleted): The fat cta tet hew eer at.

2 Repeat Expansion Nucleotide repeats are short DNA sequences that are repeated a number of times in a row. For example, a trinucleotide repeat is made up of 3-base-pair sequences, and a tetranucleotide repeat is made up of 4-base-pair sequences. A repeat expansion is a mutation that increases the number of times that the short DNA sequence is repeated. This type of mutation can cause the resulting protein to function improperly.

2 Repeat Expansion

Significance of Genetic Mutations A mutation can allow for an individual to have an advantage over other members of the species. A mutation could make an individual more camouflaged to avoid predators, faster to catch prey, or even better equipped to utilize nutrients. At the same time, some mutations can be a harmful to individuals, as is the case with genetic disorders Mutations in an individual organism can either help or hurt the chance that the individuals' genes will be passed on to offspring.

Mutation Classifications Gene mutations can be classified in two major ways: Hereditary mutations are inherited from a parent and are present throughout a person’s life in virtually every cell in the body. If the parent DNA has a mutation, the child that grows from the fertilized egg will have the mutation in each of his or her cells. Somatic mutations occur at some time during a person’s life and are present only in certain cells, not in every cell in the body. These changes can be caused by environmental factors such as ultraviolet radiation from the sun, or can occur if an error is made as DNA copies itself during cell division. Acquired mutations are not usually passed to the next generation.