Changes in DNA

Analogy  We will be using a sentence as an analogy representing a strand of DNA.  Our sentence is: The fat cat ate the wee rat.  If this sentence represents a strand of DNA, what does each word represent? (Each word represents a Codon for an Amino Acid)  What does each letter represent? (Each letter represents a Nitrogen Base in DNA.)

Mutations?!?  Now, we’re going to look at mutations in the DNA.  When you hear about mutations, you may think about some teenage turtles or growing an extra arm, but the word mutate just means change. Let’s look at what happens when we change the sentence/DNA.

Substitution The fat cat ate the wee rat. The fat cat ate the we t rat.  What changed? (Which letter is in bold?)  What does this represent? (What happened to the codon of wee?)  How would this type of change affect the protein? (How could this affect the shape? Think of the wires we used last week)

Deletion The fat cat ate the wee rat. The fat cat att hew eer at.  What changed? (Which letter is missing)  What does this represent? (How did it change everything?)  How would this type of change affect the protein? (How does that change the protein?)

Insertion The fat cat ate the wee rat. The fa b tca tat eth ewe era t.  What changed? (What was added?)  How would this type of change affect the protein? (How severe is the change in the code?)

Point Mutations vs. Frameshift Mutations  The substitution example was a point mutation.  These last two examples of deletion and insertion were frameshift mutations.  What’s the difference between a point mutation and frameshift mutation? (What code has the least severe change?)  Which has the most significant impact on the protein? Why? (Which two mutations have the most severe change in sequence?)

Synonymous (“Silent”) Point Mutations  What do you think a synonymous (“silent”) point mutation is?  Do not cause a change in the amino acid sequence  Generally, do not cause a change in the protein— however, can reduce the amount of a specific protein the cell makes or cause the structure of the protein to be changed in a manner that disrupts its functioning in the body  Example:  TAT changed to TAC—both still code from Tyrosine  CTC changed to CTA—both still code for Leucine

Inversion The fat cat ate the wee rat. The fat tar eew eht eta tac.  What changed? (Try reading the bold backwards)  How would this type of change affect the protein? (What does this do to the codon sequence?)

Chromosomal Mutations What changed? (Look at the blue part) How would this type of change affect the protein? (If you have the same code twice, how many proteins do you make?

Chromosomal Mutations What changed? (Compare the after to the before) How would this type of change affect the protein? (Same instructions twice mean what?)

Chromosomal Mutations What changed? (look at the lengths) How would this type of change affect the protein? (imagine 4 is for blood, 20 is for hair)

Non-Disjunction Ex: Trisomy 21 or Down Syndrome  Sometimes, there is an error in meiosis when egg or sperm cells divide resulting in too many or too few chromosomes.  How do you think this type of change would impact an organism?

Down Syndrome – Trisomy 21  Many people with Down syndrome have poor strength, poor muscle mass, and high body fat percentage and so are disposed to cardiovascular health problems. Although physical fitness has been suggested to improve physical and psychosocial health for a variety of healthy patient populations, information about the safety and effectiveness of aerobic exercise for adults with Down syndrome is lacking. This review identified only three small randomized trials. The results showed that only aspects of work performance (for example, maximal test time, maximal distance at the end of the exercise test) were improved after aerobic exercise training programs. Further well ‐ designed research on larger population samples is required to evaluate potential benefits for psychosocial aspects in adults with Down syndrome.

Mutation Impact  The impact of a mutation on an individual also depends on where and when it occurs.  If there was a mutation in the DNA of a zygote, how would that impact the individual?  How might a mutation in a skin cell affect an individual?

Pedigree Charts  Pedigree charts are like a genetic family tree.  They can use family information to trace genetic conditions that have been passed along in the family ( genetic conditions caused by mutations ).  Genetic counselors use them to help people analyze their family history and determine the probability of them having or passing on a particular condition ( mutation ).

Pedigree Chart Symbols  Empty Square = male  Empty Circle = female  Filled/Darkened Square = affected male  Filled/Darkened Circle = affected female  Square/Circle with Slash through = deceased individual

Pedigree Chart Example