lecture 13- gene mutation and transposable elements

Question 1

mutations

Answer 1

a mutation could be as small as a change in a single DNA base pair and go up to large change in a chromosome structure

Question 2

somatic mutation

Answer 2

affect only the individual in which they arise (not transmitted to progeny)

Question 3

germline mutations

Answer 3

alter gametes, affecting the next generation. (transmitted to progeny)

Question 4

base substitution

Answer 4

replaces one base with another

Question 5

transitions

Answer 5

converts purine to purine and pyrimidine to pyrimidine ( A to G or T to C)

Question 6

transversions

Answer 6

convert purine to pyrimidine or to a pyrimidine to purine ( A to T or C to G)

Question 7

silent or synonymous mutations

Answer 7

occur when mutant codon encodes the same amino acid as in wild-type gene, so that no change occurs in protein produced ( AGA and AGC both encode arg)

Question 8

nonsense mutations

Answer 8

change codon in open reading frame (ORF) to stop codon, resulting in premature termination of translation and truncated (often nonfunctional) protein (AAG coding lys to stop codon TAG)

Question 9

conservative (neutral) missense mutation

Answer 9

change codon in ORF, but resulting a.a. is similar to one substituted, producing no detectable change in protein function (AGA to AAA substitutes Arg for Lys: a.a.’s have similar properties, so protein function may be altered)

Question 10

non-conservative missense mutation

Answer 10

change codon in ORF resulting in different a.a. to one substituted, producing change in protein function (AGA to ATA substitues for Arg for lle: a.a.’s have different properties, so protein function may well be altered)

Question 11

base insertions or deletions (InDels)

Answer 11

of base number not divisible by 3, can change reading frame of mRNA downstream of mutation: frameshift

Question 12

spontaneous

Answer 12

most mutations are spontaneous (DNA replication transposable elements). in eukaryotes the rate is 10^-4 t0 10^-6 per gene per generation

Question 13

depurination

Answer 13

deconnection of G or A from DNA sugar-P backbone usually is repaired

Question 14

deamination

Answer 14

removes an amino acid group from a base (NH2 removed from C will become uracil. if not repaired, CG will convert to TA (transition))

Question 15

induced

Answer 15

exposure to physical and chemical mutagens

Question 16

radiation

Answer 16

• x-ray and other ionizing radiation- breakage of covalent bonds
• UV irradiation- cross linkage between adjacent pyrimidine bases

Question 17

chemical mutagen

Answer 17

• base modifying agents- ethyl methanesulfonate

Question 18

loss of function

Answer 18

also known as null mutation. if eliminates crucial function of a gene- are in general recessive mutations

Question 19

leaky mutatiosn

Answer 19

reduced function; inactivation is incomplete

Question 20

gain of function

Answer 20

confers a new function on the gene- are in general dominant mutations