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?  What does each letter represent?

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 wet rat. What changed? E changed to T

What does this represent (description)?Change in one nucleotide in a codonHow would this type of change affect the protein (significance)? May or may not Change the amino acid

Deletion

The fat cat ate the wee rat.The fat cat att hew eer at. What changed? The e was taken off “ate”

What does this represent?one nucleotide is taken out and everything shifts to the leftHow would this type of change affect the protein? The remaining codons have changed. This may shorten protein or make it ineffective.

Insertion

The fat cat ate the wee rat.The fab tca tat eth ewe era t. What changed? Inserted a nucleotide and everthing shifted to the right

How would this type of change affect the protein? Make protein shorter or ineffective

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?

Which has the most significant impact on the protein? Why?

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? Last portion of sentence was reversed

How would this type of change affect the protein? It will invert the amino acid sequence so it may result in an ineffective protein

Chromosomal Mutations

•What changed?portion of chromosome duplicated

•How would this type of change affect the protein? Amino acid is duplicated

Chromosomal Mutations

•What changed? Portion of chromosome is deleted

•How would this type of change affect the protein? Fatal, genetic disorders, muscular atrophy

Chromosomal Mutations

•What changed?Chromosomes are rearranged

•How would this type of change affect the protein?destroys gene function causing abnormal number of chromosomes

Non-DisjunctionEx: 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?

causes an abnormal number of chromosomes

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