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Understanding Mutations: Types, Effects, and Causes

This article explains the different types of mutations, their effects on genes and chromosomes, and the factors that cause them. It also discusses how mutations can impact an organism's phenotype and create genetic variation.

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Understanding Mutations: Types, Effects, and Causes

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  1. Warm-Up • Write the amino acid and mRNA sequence that would go along with the incomplete tRNA molecules • What other part of a cell would be directly involved with the tRNA? UAC GGU AAA CGU

  2. 8.7 Mutations

  3. Mutations can effect a single gene or an entire chromosome • Mutation- a change in an organism’s DNA • Usually mutations that affect a single gene happen during replication while one that affects many genes or an entire chromosome happen during meiosis (replication of gametes- eggs and sperm)

  4. Gene Mutations • 2 types: • Point mutation • One nucleotide gets substituted for another • Most often mistake is caught by DNA Polymerase but if not, it will continue to be replicated • Frameshift mutation • Insertion or deletion of a nucleotide • Generally has a worse effect on the protein than point because it shifts the whole sequence

  5. Example of Frameshift Mutations • From page 252 • Consider this DNA nucleotide sequence: THE CAT ATE THE RAT • Now if you had a deletion of the E in the first THE, look what happens: THC ATA TET HER AT… • What has happened to the reading frame? How would this effect the mRNA strand (and therefore the sequence of amino acids)?

  6. Chromosomal Mutations • Can result in duplicate or missing copies of entire genes gene duplication/deletion • Can result in a piece of one chromosome connecting to a piece of a nonhomologous chromosomes (a different chromosome, the wrong one) gene translocation *we will discuss chromosomal mutations in more detail after we talk about meiosis

  7. Mutations may or may not affect phenotype • Phenotype- physical characteristics • Whether it affects it or not depends on number of genes involved, location of the mutation, function of gene etc • Mutations that occur in body cells ONLY affect that organism • Mutations that occur in germ cells (eggs and sperm) can affect offspring • This is what creates genetic variation, the basis of natural selection

  8. What Causes Mutations? • Natural replication errors missed by DNA replication • These accumulate over time (one major cause of aging) • Mutagens • Agents in the environment that can change DNA • Can break DNA strands • Can speed up the rate of replication errors • Natural sources (like UV light) and chemicals (like cigarettes)

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