Chapter 14 GENETIC VARIATION

Overview Normal genetic variation: due to the alleles and the characteristics that they code for (ex: flower color) Abnormal genetic variation: when genes are altered from their normal sequence Mutation: a process, condition, or event which alters a gene or segment of DNA

Normal Genetic Variance Critical for the survival of a population Arises during meiosis Occurs by independent assortment and crossing over (see figure 14.2.2)

Abnormal Genetic Variants Mutations are a change (from parent to offspring) in the normal sequence of a gene. Usually cause severe problems, usually results in death On rare occasions mutation can be the source of a normal genetic variation

DNA Molecule Review Only 1% of DNA is made up of genes that code for protein production. See picture on page 248 The rest is made up of RNA genes, tandem repeats, and pseudogenes

Mutation Errors in the normal sequence of DNA Copying errors: during mitosis or meiosis a base is replicated incorrectly. Proteins need the correct sequence of amino acids in order to work properly; altering just one nucleotide base can result in the death of the organism. Mutations, once they occur, are permanent.

Germ cell mutation: are transmitted to gametes; passed to every cell in the organism formed from a mutated gamete. Somatic mutation: occurs after the organism is formed; not passed between generations. ie. cancer cells

Point mutation: alters a single base (nucleotide) Types: Substitutions: one base is substituted for another. a. Missense mutation: changes one of the amino acids in the protein b. Silent mutation: does not change the amino acid; least harmful c. Nonsense mutation: changes the amino acid to a stop code.

2. Deletions: a nucleotide is left out of its proper sequence; a base is lost. May cause a reading frame shift. 3. Additions (insertions): when a single nucleotide is added during replication.

Chromosomal mutations: changes in large segments of DNA Crossing over: occurs when homologous chromosomes exchange pieces during meiosis 2. Deletion: when an entire segment of the chromosome is deleted, or removed during DNA replication 3. Inversion: a piece of chromosome breaks off, turns upside down, and reattaches at a different place.

4. Duplication: a piece of broken off 4. Duplication: a piece of broken off chromosome inserts into the homologous chromosome. 5. Translocation: the chromosomal material breaks off and insert into a non- homologous chromosome. 6. Nondisjunction chromosomal mutation: the homologous chromosomes do not separate during Meiosis I. (one gamete receives too many chromosomes) 7. Mutagens: environmental conditions cause changes in the normal DNA structure

Mutation in Somatic vs. Germ cells Germ cell mutations are passed from parent to offspring. Somatic cell mutations are not.