Mechanisms of Genetic Variation

Question 1

What are the 2 ways genetic change can occur?

Answer 1

mutations and homologous genetic recombination

Question 2

what are mutations?

Answer 2

Stable, heritable changes of sequence of bases in DNA (or RNA in RNA viruses)

Question 3

what are point mutations (3)

Answer 3

• most common type of mutations
• mutation due to the alteration of single pairs of nucleotide
• due to the addition or deletion of a few nucleotide pairs

Question 4

larger mutations are less common and more severe. Name some (5)

Answer 4

insertions, deletions, inversions, duplication, and translocation of nucleotide sequences

Question 5

are mutations usually detrimental or beneficial

Answer 5

usually detrimental, very rarely beneficial

Question 6

what are the two mutations?

Answer 6

induced and spontaneous

Question 7

describe spontaneous mutations (4)

Answer 7

1. ) arise without exposure to external agents
2. ) may results from errors in DNA replication
   - due to base isomerization resulting in base-pair substitution mutations
   - due to insertion or deletion of nucleotides
3. ) many result in errors in the repair of DNA or homologous recombination
4. ) May also result from the action of mobile genetic elements such as transposons

Question 8

describe induced mutations (3)

Answer 8

• Arise from the exposure to certain chemical or physical agents called mutagens
• May result from direct damage of mutagens to DNA which might cause mispairing errors in DNA replication
• May results from errors in the repair of damaged DNA

Question 9

what are the 3 types of mutations? describe

Answer 9

-Base-pair substitution Mutation – change of one base-pair to a different base pair
-Base insertions or deletions – addition or deletion of one or a few base-pairs
-Frameshift mutations – addition or deletion of one or a few base-pairs which shifts the translational reading frame in mRNA and produces an incorrect polypeptide
(slides 8-11)

Question 10

slides 12-16

Answer 10

Definitely look at 12. Others are pictures and videos

Question 11

in relation to point mutations, in protein-coding sequences genes can affect protein structure in a variety of ways. What are these different ways?

Answer 11

1. ) Have no effect on protein structure or function
2. ) Change protein structure but no effect on function
3. ) Change structure and function
   - enhance function
   - abolish function
   - change to new function

Question 12

What are the different types of point mutations? describe (4)

Answer 12

1.) Silent mutation – change nucleoside sequence of codon – but not the encoded amino acid
2.) Missense mutation – a single base substitution that changes codon for one amino acid into codon for another amino acid
3.) Nonsense mutation – converts a sense codon to a stop codon
4.) Frameshift mutation – results from insertion or deletion of one or two base pairs in the coding region of the gene
(slides 20-21?)

Question 13

describe mutations in regulatory sequences

Answer 13

• do not affect protein structure, but might affect its regulation
• might increase transcription, decrease transcription, abolish transcription

Question 14

mutations in tRNA and rRNA genes disrupt what?

Answer 14

protein synthesis

Question 15

describe proofreading during replication (2)

Answer 15

-correction of errors in base pairing made during replication by DNA polymerase
-mismatch repair enzymes
(slide 25)

Question 16

describe excision repair (3)

Answer 16

-Corrects damage that causes distortions in double helix
-Two types of repair systems are known
1. nucleotide excision repair
2. base excision repair
-both remove the damaged portion of the DNA strand and use the intact complementary strand as a template to synthesize new DNA
(slide 26-28)

Question 17

describe error prone repair (5)

Answer 17

• When DNA damage is large scale the cell may need to use a different type of repair system (i.e., damage interferes with DNA replication)
• This system is more error prone – IT CAN LEAD TO MUTATIONS
• Allows replication to proceed and cell to replicate, but errors are more likely
• Mechanism called the SOS regulatory system in E. coli
• Translesion synthesis allows DNA to be synthesized with no template

Question 18

each mutant form that survives becomes an _____, an alternate form of a gene

Answer 18

allele

Question 19

_______is the process in which one or more nucleic acids are rearranged or combined to produce a new nucleotide sequence (recombinants)

Answer 19

Recombination

Question 20

what is vertical gene transfer?

Answer 20

transfer of genes from parents to progeny

Question 21

In eukaryotes
sexual reproduction is accompanied by genetic recombination due to
(2 things)

Answer 21

• crossing over between sister chromatids during meiosis

- fusion of gametes

Question 22

Horizontal Gene Transfer (HGT) in Bacteria and Archaea differs from vertical gene transfer

Answer 22

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