SC.912.L.16.4 Explain how mutations in the DNA sequence may or may not result in phenotypic change. Explain how mutations in gametes may result in phenotypic changes in offspring.

Bellringer Mutations are random changes in the genetic code of an organism that may occur in any of the cells of an organism. The altered code may have no effect on the organism. However, it may produce a trait that is harmful or helpful to the individual. Which cells can have a mutation that could be passed on to offspring? Egg cells of an animal Leaf cells of a plant Skin cells of an animal Blood cells of an animal

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

A mutation is a change in an organism’s DNA. Some mutations affect a single gene, while others affect an entire chromosome. Many kinds of mutations can occur, especially during replication. The two most common types of gene mutations are 1.) point and 2.) frameshift.

A mutation is a change in an organism’s DNA. A point mutation substitutes one nucleotide for another and could change the amino acid. mutated base

A mutation is a change in an organism’s DNA. A frameshift mutation inserts or deletes a nucleotide and always changes the amino acid.

A mutation is a change in an organism’s DNA.

Chromosomal mutations These mutations affect many genes. They often occur during crossing over. Ex.: Gene duplication and translocation Teacher note: Depending on your student population, their data, and previously taught content, you may need to review the distinctions between gene duplication and translocation. On this slide (duplication), point out that the resulting chromosome on the right would have 2 copies of certain genes: (1) its original “green” version of the gene and (2) the new purple version of the same gene that was transferred from the purple chromosome (duplication is also on the next slide). Translocation will be noted on the following slide (#12).

Chromosomal mutations – Gene duplication Occurs due to unequal crossing over. Teacher note (as mentioned on the last slide): Depending, on your student population, their data, and previously taught content, you may need to review the distinctions between gene duplication and translocation. On this slide (duplication cont’d), point out that the resulting chromosome on the right would have 2 copies of certain genes: (1) its original “green” version of the gene and (2) the new purple version of the same gene that was transferred from the purple chromosome (duplication was also on the previous slide). Translocation will be noted on the next slide (#12).

Chromosomal mutations - Translocation Occurs when two non-homologous chromosomes exchange DNA segments. Teacher note: This figure, which is very similar to the one seen on slides 10 & 11, can be used to explain translocation, the general condition of having a DNA exchange of two non-homologous chromosomes. This translocation is reciprocal (one of two common versions of translocations), and the new combinations of DNA are likely to result in mutation.

Mutations may or may not affect the phenotype of an organism. Review: What is the phenotype of an organism? Chromosomal mutations tend to have a big effect because they are affecting a large amount of DNA and almost always change the phenotype.

Mutations may or may not affect the phenotype of an organism. Gene mutations affect a small area of DNA and may change the phenotype. When the phenotype is not changed, it is called a silent mutation. Ex: If a gene mutation occurs in a non- coding region, it would not change the phenotype. Teacher note: the next slide is an optional one that can be used/revealed (if needed) to explain a silent mutation.

Mutations may or may not affect the phenotype of an organism. Mutations in somatic (body) cells are not passed on and do not affect offspring. Mutations in gametes (sex cells) are passed on (if that gamete is the egg or sperm that forms the zygote).

Mutations may or may not affect the phenotype of an organism. Mutations are not always negative. They can be harmful or beneficial. Natural selection often removes mutant alleles from a population when they are less adaptive.

Causes of Mutations Errors during DNA replication or crossing over. Mutagens – physical or chemical agents that change the DNA and cause an increase in the likelihood of mutations. Ex: UV Rays, toxic chemicals Some cancer drugs use mutagenic properties to kill cancer cells.

We Do - Practice Test your knowledge of mutations by reviewing information sheet and then answering the questions on the Mutations Worksheet.

RE-TRY Mutations are random changes in the genetic code of an organism that may occur in any of the cells of an organism. The altered code may have no effect on the organism. However, it may produce a trait that is harmful or helpful to the individual. Which cells can have a mutation that could be passed on to offspring? Egg cells of an animal Leaf cells of a plant Skin cells of an animal Blood cells of an animal

Re-TRY Mutations are random changes in the genetic code of an organism that may occur in any of the cells of an organism. The altered code may have no effect on the organism. However, it may produce a trait that is harmful or helpful to the individual. Which cells can have a mutation that could be passed on to offspring? Egg cells of an animal – Why? Leaf cells of a plant Skin cells of an animal Blood cells of an animal

You Do (exit slip) Questions The following questions can be projected when an instructor reaches the “You Do” portion of the lesson or the handout can be used.

Exit slip questions A chemical spill from a manufacturing plant into the local water supply is found to contain a known mutagen that produces deletions in mammalian DNA. Which description in the chart below most accurately describes what occurs when a DNA nucleotide is deleted from a gene? Gene… Trait controlled by the original DNA… A is not changed is never changed B could be changed C is changed D Answer: D

Exit slip questions Choose the answer choice that correctly fills in both blanks in the sentence below. Sometimes when a point mutation happens, it changes the nucleotide in the DNA, but it doesn’t change the amino acid in the protein. This type of mutation is referred to as a ________________ mutation because it _________________ cause a change in the phenotype. A. deletion / does not B. silent / does not C. frameshift / does D. nonsense / does Answer: B

Exit slip questions 3. In a person who has Tay-Sachs disease, there is a mutation in the DNA caused by the addition of 4 nucleotides? Using the provided genetic code chart, what type of mutation is illustrated here and why would there be a change in the amino acid sequence? silent mutation; the extra bases would not affect the translated protein frameshift mutation; generation of similar codons would produce the same protein silent mutation; one amino acid would be different but the rest would remain unaltered D. Frameshift mutation; the inserted bases would result in an abnormal protein after the insertion point Answer: D

Genetic Code Chart