Gene Mutations

Question 1

How do mutations occur?

Answer 1

randomly

Question 2

How often do mutations occur?

Answer 2

rarely

Question 3

How do spontaneous mutations occur?

Answer 3

mutations that arise mainly through errors in DNA replication (without exposure to mutagens)

Question 4

How do induced mutations arise?

Answer 4

through the exposure to mutagens (often called carcinogens)

Question 5

When are mutations heritable?

Answer 5

When they occur in germ-line cells they will end up in sperm or egg and be passed on

Question 6

When are mutations not heritable?

Answer 6

when they occur in somatic cells

Question 7

How do mutations change the DNA?

Answer 7

Substitute
add
delete
one or more DNA base pairs

Question 8

Where do point mutations occur?

Answer 8

at specific, identifiable position in a gene
or
a specific location in the genome

Question 9

Describe base-pair substitution mutations

Answer 9

the replacement of one nucleotide base pair by another

Question 10

What are the 3 types of base-pair substitution mutations?

Answer 10

synonymous
missense
nonsense

Question 11

Describe synonymous mutations

Answer 11

a base-pair change that does not alter the result of the amino acid

Question 12

Why do synonymous mutations occur?

Answer 12

because of the redundancy of the genetic code and the wobble position

Question 13

Describe missense mutations

Answer 13

a base-pair change that results in an amino acid change in the protein

Question 14

Describe nonsense mutations

Answer 14

base-pair change that creates a stop codon instead of a regular codon for an amino acid

Question 15

Describe frameshift mutations

Answer 15

when there is an insertion or deletion of one or more base pairs in the coding region of a gene that changes the reading frame of the message

Question 16

Where does the frameshift mutation occur? What does this change cause?

Answer 16

in the mRNA

it alters the reading frame of the message

Question 17

What are the consequences of frameshift mutations?

Answer 17

premature stop codons can be produced

the wrong amino acid sequence can be produced starting from the point of mutation

Question 18

Describe mutations in regulatory regions/noncoding regions

Answer 18

mutations that change the amount of protein produced by a gene but not the amino acid sequence

Question 19

T or F: regulatory mutations change the amino acid sequence

Answer 19

false! they change the amount of protein produced by a gene

Question 20

What regions can regulatory mutations affect?

Answer 20

promoters
introns
regions that code for 5’-UTR and 3’-UTR

Question 21

Describe promoter mutations

Answer 21

mutations that alter consensus sequence nucleotides of promoters

Question 22

What are the consequences of promoter mutations?

Answer 22

interference of transcription initiation:

mild-moderate reductions in transcription levels

stopping transcription

Question 23

Describe splicing mutations

Answer 23

alterations of nucleotides (specific sequences) at either end of an intron

Question 24

What are the consequences of splicing mutations?

Answer 24

Splicing errors

production of mutant proteins because introns aren’t spliced

Question 25

What are the consequences of splice site mutations?

Answer 25

can dramatically change mRNA transcript can cause large insertion or deletions in mature mRNA that may or may not be in frame result in non-functioning proteins

Question 26

What do splicing mutations often result in?

Answer 26

non-functioning proteins

Question 27

Describe cryptic splice sites and how they form

Answer 27

new splice sites that can replace or compete with authentic splice sites formed by base-pair substitution during mRNA processing

Question 28

Give an example of cryptic splice sites

Answer 28

A base-pair substitution that changes G to A at position 110 of human beta-globin intron 1 creates an AG splice site which leaves 19 additional nucleotides in the mature mRNA

Question 29

Describe polyadenylation mutations

Answer 29

alteration of the signal sequence for the addition of the Poly-A tail at the 3' end of eukaryotic mRNA which causes blocking of 3' processing of mRNA

Question 30

What consequences do polyadenylation mutations have?

Answer 30

they reduce the amount of protein produced: reduce ability of mRNA to leave nucleus for translation make mRNA more vulnerable to degradation before translation (parts of mRNA may be lost)

Question 31

Describe a null mutation

Answer 31

When a mutation within a gene causes loss of function and produces no functional gene product

Question 32

Describe leaky mutations

Answer 32

A mutation within a gene that causes partial loss of function and produces a partially functional gene product

Question 33

Describe a silent mutation

Answer 33

a mutation within a gene that produces a normally functioning gene product

Question 34

What does the severity of the phenotype of a leaky mutation depend on?

Answer 34

the level of activity of the gene product

Question 35

What type of mutations will result in a null mutation product?

Answer 35

``` promoter mutations frameshift mutations nonsense mutations splicing mutations missense mutations (less common) ```

Question 36

What type of mutation will cause leaky mutations?

Answer 36

missense mutations

Question 37

What type of mutation will cause silent mutations?

Answer 37

synonymous mutations

Question 38

What are the terms dominant and recessive based on?

Answer 38

phenotypes

Question 39

What determines the dominance of one allele over another?

Answer 39

the protein product of the alleles

Question 40

What are phenotypes the result of?

Answer 40

the activities of the protein products of the alleles of a gene

Question 41

Are mutations of haplosufficient genes dominant or recessive?

Answer 41

recessive

Question 42

What does a wild-type allele (R) produce in haplosufficient genes?

Answer 42

an active enzyme (50 units)

Question 43

How many units does an active enzyme produced by a wild-type allele (R) in haplosufficient genes have?

Answer 43

50

Question 44

What does a mutant allele (r) in haplosufficient genes produce?

Answer 44

no active enzyme (0 units)

Question 45

How many units does an inactive enzyme produced by a mutant allele (r) in haplosufficient genes have?

Answer 45

0

Question 46

How many units of enzyme activity are required to produce a wild-type phenotype in haplosufficient genes?

Answer 46

40+

Question 47

How many functional copies of a gene is enough for normal function in heterozygotes with haplosufficient genes?

Answer 47

one remember that Rr will display the dominant phenotype - only required one functional copy (R)

Question 48

Are mutations of haploINsufficient genes dominant or recessive?

Answer 48

dominant

Question 49

What does allele T1 in haploinsufficient genes produce?

Answer 49

an active enzyme (10 units)

Question 50

How many units does an active enzyme from T1 allele in haploinsufficient genes produce?

Answer 50

10 units

Question 51

What does the mutant allele T12 in haploinsufficient genes produce?

Answer 51

a less active enzyme (5 units)

Question 52

How many units does the less active enzyme produced by mutant allele T2 in haploinsufficient genes have?

Answer 52

5 units

Question 53

How many units of enzyme activity is required to produce the wild-type phenotype in haploinsufficient genes?

Answer 53

18+ (only T1T1 individuals are WT)

Question 54

Using the T1 and T2 key, what genotype would individuals with haploinsufficient genes have to have to express the WT phenotype?

Answer 54

T1T1 (homozygous) because the mutation (T2) is dominant in haploinsufficient genes

Question 55

Using the T1 and T2 key, what genotype would individuals with haploinsufficient genes have to have to express the mutant phenotype?

Answer 55

either T1T2 or T2T2 because neither produces enough enzyme to make the WT phenotype

Question 56

In haploinsufficient genes, how many functional copies of a gene are required for normal functioning (the production of the WT phenotype)?

Answer 56

More than 1