Linkage and Mapping
If there is 200 children in a generation, what would the distances between genes A and B be if there is 50 recombinant children?
25 map units
Do members of a complementation group have mutations in the same gene or different genes?
What is the same gene?
The Meselson and Stahl experiment pointed to DNA having which type of replication model?
What is the semi-conservative model?
What is the difference between a forward vs. reverse mutation?
Forward mutations are when a wild-type allele is changed into a different allele. Reverse mutations are when a mutant allele reverts into a wild-type allele.
Forward mutations are much more prominent than reverse.
If there is a distance of 70 map units between gene A and gene B on the same chromosome, what is the expected recombination frequency for the filial generation?
50%
What do the + and - symbols mean in a complementation table?
+ means mutations are in different genes and different complementation groups
- means mutations are in same gene and same complementation groups
List the correct order of enzymes used in DNA replication.
1. RNA primase
2. DNA polymerase
3. Helicase
4. DNA ligase
3, 1, 2, 4
What type of mutation are transition and transversions? Describe what a transition and transversion mutation is.
These are point-substitution mutations. Transition mutations- when a purine is substituted for a purine or pyrimidine for a pyrimidine.
Transversion mutations- when a purine is substituted for a pyrimidine or vice versa.
A plant of genotype AB/ab is back-crossed to ab/ab, and 30% of the progeny obtained is ab/ab. What is the
genetic distance between A and B genes?
40 map units
https://docs.google.com/document/d/1Ei26m0nl5qW2PqRbcYjVF-oq0hoLXZNCI01FaVPjufI/edit?usp=sharing
Which mutations are grouped together?
3, 5, 8
2, 6, 7
1, 4
If 20% of bases in a region of the frog genome are adenine, what percent of bases in that region are cytosine?
30%
What kind of mutations arise from X-rays vs. UV light?
X-rays create double-stranded breaks and UV light creates thymine-thymine dimers.
Genotypes: Number of progeny
a B C: 50
a b C: 328
a B c: 115
a b c: 20
A B C: 10
A b C: 115
A B c: 312
A b c: 50
Draw a genetic map, including genetic distances.
Parents: a b C and A B c
DCOs: a b c and A B C
C is middle gene and total map units is 39 mu.
A - 26 mu - C - 13 mu - B
https://docs.google.com/document/d/1Ei26m0nl5qW2PqRbcYjVF-oq0hoLXZNCI01FaVPjufI/edit?usp=sharing
Draw the biochemical pathway.
B --> D --> C -->A --> His
M4 M2 M6 M8
What two cuts can be made at Holliday junctions that don't result in crossing over? Name all of them.
Two horizontal cuts or two vertical cuts
Describe what the 2 mechanisms of double-strand break repair are.
Homologous recombination is when the exonuclease chews back the damaged DNA and strand invasion promotes repair (sister chromatid is the template).
Nonhomologous end joining is when the proteins bind to exposed ends to protect them from nucleases and DNA ligase glues everything together.
You perform a dihybrid cross with two F1 generation plants containing yellow, round seeds (heterozygotes). From this cross, you obtained 600 yellow, round progeny, 155 yellow, wrinkled progeny, 160 green, round progeny, and 85 green, wrinkled progeny. Perform a chi-squared analysis to determine if the genes are linked and explain your results. (You can look up the chi-square value table)
Null hypothesis rejected. Genes are linked.
Crick and Brenner treated T4 phage with the mutagen proflavine and then isolated two rIIB
mutant strains (those that give large, mutant plaques), which they named FC4 and FC5. Describe the results of an experiment where they co-infect with both FC4 and FC5 and what the results mean.
If they see only mutant plaques, then they would know the mutants are of the same type. If they see mostly mutant plaques but a few wildtype plaques, then they would know that these strains
carry different types of mutation.
https://docs.google.com/document/d/1E6UJqOAgXTgyuA5yU6yGuk78PinbSYeKFDqDNcnSOyg/edit?usp=sharing
In a recombination event, if Holliday junctions are cut in the pattern below, how would the resulting DNA strands look? Assume any gene conversion returns nucleotides to their original pairing.
https://docs.google.com/document/d/1yMh3S6Zt_N0hRZZEk1FuhAUgMwLJq_cGSvUS05prBxQ/edit?usp=sharing
The blue and red overlap on chromatid 2 and chromatid 3 are the heteroduplexes that are formed when homologous DNA strands pair up. Since it says that gene conversion returns nucleotides to their original pairing, the heteroduplex on chromatid 2 becomes b and the heteroduplex on chromatid 3 becomes B.
What are the purpose, components, and expected results of the Ames Test?
The Ames test is used to identify potential carcinogens. The potential mutagen, His-mutant bacteria, and rat liver enzymes (which mimic human metabolic processes) are mixed and plated on a histidine-free medium. If there are many bacterial colonies present that displays many His- to His + revertants and confirms that the potential mutagen is a mutagen.