8.7 Mutations KEY CONCEPT Mutations are changes in DNA that may or may not affect phenotype.

8.7 Mutations A mutation is a change in an organism’s DNA. Many kinds of mutations can occur, especially during replication. Most mutations are repaired by organism’s enzymes and have no effect. If not repaired, the altered gene/chromosome will be passed to daughter cells.

8.7 Mutations Mutations in body (somatic) cells verses gametes. In a somatic cell, daughter cells are affected by the DNA but not the offspring of the organism. –Body cell mutations contribute to aging or the development of cancer. If the mutant is a gamete (sex cell), the altered DNA will be transmitted to the embryo and may be passed on from generation to generation. These cause genetic disorders. If the mutation affects a gene, then it’s a gene mutation. If the mutation affects a chromosome or multiple genes it’s a chromosomal mutation.

8.7 Mutations Gene Mutation Examples A point mutation substitutes one nucleotide for another. Example disorders: Tay-Sachs disease, Sickle Cell mutated base

8.7 Mutations –A frameshift mutation inserts (insertion) or deletes (deletion) a nucleotide in the DNA sequence. Frameshift Mutation

8.7 Mutations –Gene duplication results from unequal crossing over. Chromosomal mutations may occur during crossing over Chromosomal Mutations

8.7 Mutations Translocation results from the exchange of DNA segments between nonhomologous chromosomes.

8.7 Mutations Deletion Duplication Inversion Translocation Figure 12–20 Chromosomal Mutations Section 12-4

8.7 Mutations Nondisjunction Usually occurs during meiosis and can cause gametes to lack a chromosome or have an extra chromosome. –Example: An egg may have 22 or 24 chromosomes. If a zygote has only 45 chromosomes then one pair has only one chromosome (monosomy). If a zygote has 47 chromosomes then there are 3 copies of one chromosome (trisomy). –Example disorders: Down syndrome, klinefelter’s syndrome and Turner’s syndrome

8.7 Mutations Turner Syndrome Nondisjunction

8.7 Mutations Mutations can be caused by several factors. Replication errors can cause mutations. Mutagens, such as UV ray and chemicals (carcinogens), can cause mutations. Some cancer drugs use mutagenic properties to kill cancer cells.

8.7 Mutations Mutations in body cells do not affect offspring. Mutations in sex cells can be harmful or beneficial to offspring. Natural selection often removes mutant alleles from a population when they are less adaptive. Beneficial mutations may be useful to organisms in changing environments. These mutations may be favored by natural selection.