Exam 3 Flashcards
Does a mutation have to be inherited?
Yes!
What is a somatic mutation?
A mutation in a non-reproductive cell
What does a somatic mutation do?
It generates a mosaic because some cells have the mutation and some don’t. Only descendants of the original mutation carry the mutation
What is a germline mutation?
A mutation in reproductive cells. The parent does not show a mutation but the offspring either show or do not show mutation
What is a codon?
3 nucleotide sequence that codes for a specific amino acid
What is a reading frame?
The series of codons that code for amino acids, starts at the start codon (AUG) that codes for Met
What is a transition mutation?
Mutation that changes pyrimidine to pyrimidine or purine to purine
What is a transversion mutation?
A mutation that changes purine (A/G) to pyrimidine (T (U)/C or vice-versa
What is a missense mutation?
A mutation that results in a different amino acid. This may or may not effect the phenotype
What is a nonsense mutation?
A mutation that results in a stop codon. Results in translation ending prematurely, severe phenotype effect
What is a silent mutation?
A mutation that does not alter the amino acid sequence, it has no phenotype effect
What is a forward mutation?
A mutation that alters the wild-type phenotype, a new mutation
What is a reverse mutation?
A mutation that reverses a forward mutation to go back to the wild-type. This is very rare.
What is a suppressor mutation?
2 different mutations occur on different genes. The combination of the two mutations causes the phenotype to go back to the original. This is for intergenic
What about a intragenic suppressor mutation?
The 2 mutations that reverse the first mutation occur at different sites on the same gene
What are the 3 main causes of mutation?
1) DNA replication errors, 2) DNA damage after replication, 3) Transposons or viral insertions after replication
How do DNA replication errors work?
If all of the review techniques do not catch the mutation, the mutation is fixed. This occurs during replication. This could be with point mutations or expanding trinucleotide repeats where mispairing occurs and extra repeats are formed
What happens in tautomeric shifts?
A proton shifts and the base is converted from the common form to the rare form. This causes incorrect base pairing. The base usually shifts back but the mutation is already recorded.
What happens with base analogs?
Chemicals with structures similar to bases can get ionized and pair wrong to cause a mutation
What happens with chemically induced mutations?
Mutagenic agents modify bases and cause misspairing
What happens in radiation induced mutations (X-rays, gamma rays, cosmic rays)
The radiation causes DNA damage either by altering the structure of bases, breaking bonds, and introducing double stranded DNA breaks
What happens with UV radiation caused mutation
This causes thymine dimers which distort the DNA and block replication.
What is a transposon?
Mobile genetic information that moves semi-autonomously and inserts randomly into the genome
What is the general structure of transposons?
A middle, inverted repeats
What is replicative transposition?
copy and paste, the transposon replicates itself and the 2nd copy inserts into the genome
What is non-replicative transposition?
cut and paste, the original transposon cuts itself out and inserts into genome
What is retrotransposition?
It is where a transposon is transcribed to RNA and then reverse transcriptase turns the RNA to DNA and a 2nd DNA strand is synthesized then the full transposon now double stranded is inserted in the genome
What are the 2 types of mutagenic effects of transposons?
Gene disruption and chromosome rearrangement
What happens with gene disruption and what is an example of this?
The transposon inserts and disrupts gene. Color in grapes- black without transposon, green with transposition, red with partial removal of transposon
What happens with chromosome rearrangement?
2 transposons insert and they pair during mitosis, they cause a deletion or a duplication
What are the 3 types of bacterial transposons?
Insertion sequence, composite, and non-composite
What is an insertion sequence transposon?
The simplest bacterial transposon that only has an insertion sequence and info for movement
What is a composite transposon?
A transposon made up of 2 insertion sequences that can mobilize independently or together, when they move together they can carry the gene between the insertion sequences with them.
What is the non-composite transposon?
A transposon that doesn’t require an insertion sequence. It is just many genes and transposase. The most complex
What are the 2 types of eukaryotic transposons?
Ac=fully functional, Ds=fractured not fully functional can not move without Ac provided transposase
How does variegation happen?
Ac causes Ds to go into gene and disrupt gene. Then Ds is removed at some point during development causing pigmentation. Depending on which point during development Ds is removed, amount of pigmentation is different
What are the 3 hypothesis of evolution of transposons?
Cellular function hypothesis. genetic variation hypothesis, and selfish gene hypothesis