GENETICS EXAM 2

What are the types of mutations generally

small scale and large scale

How many bases do small scale and large scale mutations affect

small = 1-100

large = 1000+

What type of mutation is a single nucleotide polymorphism (SNP) and what does it do

small scale mutation (most common)

• switches a T for an A

What is a transition and transversion, what is more common and why ?

transition = same type of nucleotide makes a base switch (ex. purine and purine)

transversion = different nucleotide types make a base switch (ex. purine x pyrimadine)

transitions are more common since you are using bases from the same nucleotide family

Purine: A → G, G → A

Pyrimidine: A → T, T → A

How many genomes do SNP’s account for if humans have 6 million genomes

about 3-5 million, or 0.1%

Why we are so identical

In this SNP comparison, which are the rare mutations and which are the common

Why?

the 12 X’s to the left are the rare and 6 X’s to the right are common

• rare mutations are more recently found in time not affecting a large population

• common mutations have been around in the population for awhile

What type of mutations comprise of majority of human genetic variation 

rare variants because there are more sites spread across the genome compared to common variants were there are less positions at more common site 

Where is most of the variation in an INDIVIDUAL genome found

at the common sites

What are SNP’s function

unsure

What are the types of small scale mutations

• insertions/deletions - of small # of bases

• variable number of tandem repeats (VNTR) - repeating sequences of multiple bases

What causes small scale mutations

• spontaneous

• environmental factors (chemical, UV light, radiation)

What are the specific types of spontaneous small scale mutation examples

• altered base pairing 

• tri-nucleotide repeats causing slippage 

• deamination

Explain how altered base pairing causes mutations

• G will pair w/ T instead of C

• A will pair with C instead of T

If G or T is in enol form it will pair with eachother 

If A or C is in imino form it will mispair with each other 

Explain how tri-nucleotide repeats causes mutations (and what are the common sequences)

CAG, CGG, GAA

• expanded trinucleotide repeats get confused by the polymerase adding complimentary bases during DNA replication

• it will add bases to these repeats and sometimes the new nucleotides will slip out causing the polymerase to go and add new bases back to it (expansion)

• If the template loops and the polymerase misses the sequence, new bases will not be added to the new template strand (contraction)

Explain deamination causes mutations

cytidine deaminase will remove an amino group from a nitrogenous base ex. cytosine causeing it to turn into uracil which will bond to adenine instead of guanine

What chemical process causes small scale mutations

alkylating agents chemically altering base structure by donating an alkyl group

causes G to pair with T 

guanine exposed to EMS will add an alkyl group to oxygen chemically messing up the structure and bonding it to T

How does UV light cause small scale mutations

when DNA is exposed to UV light it induces thymine dimers (covalently linked T’s next to each other) 

causes distortions of DNA structure and errors during DNA replication (body able to reverse it though)

How does ionizing radiation induce small scale mutations

• both strands or single strand of DNA breaks causing loss of a base structure

How many mutations do your parents contribute to the next generation

30

What is a mismatch repair

1. mismatched pair is identified

2. the original strand is identified

3. the mismatch pair complex identifies the region with mutation

4. the exonuclease removes newly replicated nucleotides

5. the DNA polymerase will then synthesize new DNA and ligase will join the fragments

What is a direct repair and how common is it 

an enzyme repairs the molecule 

What is a base excision repair

1. deaminated C or other types of damaged bases are recognized by diff. DNA glycosylases 

2. DNA glycosylases will remove base from the DNA 

3. the endonuclease will remove the ribose sugar

4. the DNA polymerase will add a new nucleotide and ligase will join the nucleotides