Gene Mutation and Transposable Elements

Question 1

Somatic mutations

Answer 1

affect only the individual in which they arise; are not transmitted to progeny; in diploid heterozygous individuals, only dominant somatic mutations will be expressed

Question 2

Germline mutations

Answer 2

alter gametes, affecting the next generation; transmitted to progeny

Question 3

Which has more effect, early somatic mutation or late somatic mutation?

Answer 3

Early somatic mutation because it affects a larger population

Question 4

Base substitutions

Answer 4

replaces one base w/ another; two types: transitions and transversions

Question 5

Transitions

Answer 5

converts purine to purine and pyrimidine to pyrimidine; Ex: A to G or T to C

Question 6

Transversions

Answer 6

converts a purine to pyrimidine or to a pyrimidine to purine; Ex: A to T or C to G

Question 7

Silent or synonymous mutations

Answer 7

encodes for same amino acid as in wild type gene, so that no change occurs in protein produced

Question 8

Nonsense mutations

Answer 8

encodes for a stop codon, resulting in premature termination of translation and often nonfunctional protein

Question 9

What are the 3 stop codons?

Answer 9

UGA, UAA, UAG

Question 10

Conservative (neutral) missense mutation

Answer 10

changes codon in ORF, but resulting amino acid is similar to one substituted producing no detectable change in protein function; Ex: AGA to AAA substitutes Arg for Lys which have the same properties, so protein function is not altered

Question 11

Non-conservative missense mutation

Answer 11

changes codon in ORF resulting in different amino acid to one substituted, producing change in protein fucntion; Ex; AGA to ATA substitutes Arg for Ile: amino acid’s have diff. properties, so protein function is altered

Question 12

Base insertions/deletions (InDels)

Answer 12

of base number not divisible by 3, can cause frameshift mutation

Question 13

frameshift mutation

Answer 13

can change reading frame of mRNA downstream of mutation; causes a shift due to an InDel

Question 14

Spontaneous

Answer 14

most mutations are spontaneous; most of them are corrected by cellular repair system

Question 15

Depurination

Answer 15

disconnection of G or A from DNA sugar phosphate backbone; usually repaired

Question 16

Deamination

Answer 16

removes an amino group from a base; Ex: NH2 removed from C -> becomes uracil; if not repaired, CG will convert to TA (transition)

Question 17

Induced

Answer 17

exposure to physical and chemical mutagens

Question 18

X-ray and other ionizing radiation

Answer 18

breakage of covalent bonds

Question 19

UV radiation

Answer 19

crosslinking between adjacent pyrimidine bases

Question 20

Base modifying agents

Answer 20

a chemical mutagen like ethyl methane sulfonate which causes a linkage from guanine to 6-ethylquanine and thymine

Question 21

Null mutation

Answer 21

loss of function mutation; eliminates crucial function of a gene; recessive mutations

Question 22

Leaky mutation

Answer 22

reduced function; inactivation is incomplete

Question 23

Gain of function

Answer 23

conifers a new function on the gene; dominant mutations

Question 24

Transposable elements

Answer 24

randomly insert themselves in chromosomes, causing genetic changes

Question 25

In prokaryotes, what are the types of transposable elements?

Answer 25

insertional sequences (IS) and transponsons

Question 26

Insertional sequences

Answer 26

have IRs at the ends and encode transposase required for transposition

Question 27

Transposons

Answer 27

similar to IS but have additional genes

Question 28

In eukaryotes, what are the types of TEs?

Answer 28

structure is similar to prokaryotic TEs; have genes for transposition (Ac element) and integration (Ds element)

Question 29

Ds element

Answer 29

results in colorless corn compared to the wild type (pigmented)

Question 30

Ac element

Answer 30

results in spotted kernels

Question 31

What are the possible effects of TEs in eukaryotes?

Answer 31

Disruption of genes to produce a null mutation

Activation or repression of adjacent genes by disrupting a cellular promoter or by action of transposon promoters

Chromosome mutations such as duplications, deletions, inversions, translocations, or breakage