MUTATIONS Are they good or bad?

Vocab you should know… Mutation: change in the nucleotide-base sequence of a gene or DNA molecule Deletion: loss of a part of DNA from a chromosome Inversion: reversal in the order of genes, or of a chromosome segment, w/in a chromosome

More vocab… Translocation: movement of a segment of DNA from one chromosome to another, which results in a change in the position of the segment Nondisjunction: failure of homologous chromosomes to separate during meiosis I or the failure of sister chromatids to separate during mitosis or meiosis II

Mutation basics Mutations are any change/“error” in DNA replication DNA replication is very accurate The enzyme DNA polymerase “proofreads” the copied DNA & repairs most mutations Mutations can be harmful, beneficial or have no effect at all

More basics… Some mutations are caused by carcinogens i.e. uv light, radiation, toxins Mutations that affect genes that control cell division lead to cancer b/c cancer is a tumor in which the cells begin dividing at an uncontrolled rate & become invasive (they spread out)

Germ-Cell Mutations Occur in the gametes Don’t affect the organism itself Can be passed on to offspring during reproduction

Somatic-Cell Mutations Occur in the body cells Can affect the organism i.e. cancers Cannot be inherited b/c they are not found in the gametes

Lethal Mutations Often cause death, often before the organism is born Some can be beneficial – these are how natural selection occur (the organisms w/ beneficial mutations reproduce more often & spread that trait to their offspring)

Chromosome Mutations Deletion: loss of a piece of chromosome

Deletion Mutation – Rieger Syndrome

Chromosome Mutations Inversion: section of chromosome breaks off & reattaches backwards

Inversion Mutation – Hunter Syndrome

Chromosome Mutations Translocation: piece of chromosome breaks off & attaches to a nonhomologous chromosome

Chromosome Mutations Nondisjunction: chromosome fails to separate from its homologue during meiosis; resulting in one gamete receiving an extra copy of the chromosome (3 total) & another receiving none

Nondisjunction – Down Syndrome Trisomy 21

Down Syndrome cont’d

Mutation Quiz Any error in DNA replication is a/an _____. What enzyme proofreads DNA & fixes most errors? What type of mutation occurs in gametes? Why are somatic-cell mutations not inheritable? A _______ mutation is when a chromosome losses a piece of itself.

Mutation Quiz Cont’d When part of a chromosome breaks off & reattaches backwards it is a ____ mutation. When a part of a chromosome breaks off & attaches to another chromosome it is a ______ mutation. When a chromosome fails to separate from its homologue it is a _______ mutation.

Mutation Quiz Cont’d During nondisjunction one cell receives ___ copies of the chromosome, while another cell receives __. 10. Draw one of the phases of mitosis & label it.