chapter 15

Question 1

Mutation

Answer 1

a change in the nucleotide sequence that can be passed on from one cell or organism to another

Question 2

Somatic Mutations

Answer 2

occur in the body cells; passed to daughter cells in mitosis but not to offspring

Question 3

Germ line mutations

Answer 3

occur in cells that give rise to gametes; passed to offspring at fertilization

Question 4

loss of function mutations

Answer 4

gene is not expressed at all, or protein does not function; nearly always recessive

Question 5

gain of function mutation

Answer 5

produces a protein with altered function; usually dominant

Question 6

common in cancer

Answer 6

new proteins stimulate cell division

Question 7

conditional mutation

Answer 7

phenotype is altered only under certain (restrictive) conditions (example: protein may be unstable at high temperatures)

the mutation is not detectable under permissive conditions

Ex: point restriction phenotype in Siamese cats

Question 8

reversion mutation

Answer 8

the gene is mutated a second time and DNA reverts to the original sequence or to a different sequence that results in the non-mutant phenotype
many mutations occur in nonfunctional regions of DNA and don’t affect phenotype

Question 9

Point mutation

Answer 9

insertion or deletion of a single base pair, or substitution of one base pair for another
2 types of subs
- transition - the purine is replaced by the other purine
- transversion - the purine is replaced by a pyrimidine or vice versa

Question 10

silent mutation

Answer 10

substitution that results in a codon a codon that codes for the same amino acid

Question 11

missense mutation

Answer 11

substitution resulting in a codon for a different amino acid
often have no effect on protein function

Question 12

nonsense mutaion

Answer 12

substitution results in a stop codon somewhere in the mRNA
Results in a shortened protein, usually not functional

Question 13

Loss of stop mutation

Answer 13

base pair substitution that changes a stop codon to a sense codon; extra amino acids are added to the polypeptide

Question 14

Frame shift mutation

Answer 14

insertion or deletion of a base pair
Alters the mRNA reading frame (consecutive triplets) during translation; produces nonfunctional proteins

Question 15

mutations outside coding regions can have no effect or significant effects

Answer 15

• promoter mutations may alter the rate of transcription of the gene
• mutations at RNA splicing sites may lead to abnormal mRNA

Question 16

chromosomal rearrangements

Answer 16

result in extensive changes in DNA
Break and rejoin
Can be caused by damage to chromosomes by mutagens or by errors in chromosome replication

Question 17

deletion

Answer 17

chromosome breaks in two places and rejoins, leaving out part of the DNA

Question 18

duplication

Answer 18

homologous chromosomes break at different positions and reconnect to the wrong partners. Can also be caused by inappropriate followed by crossing over

Question 19

inversion

Answer 19

chromosome breaks and rejoins with one segment flipped

Question 20

translocation

Answer 20

segment of DNA breaks off and attaches to another chromosome; can cause duplications and deletions
Downs Syndrome is caused by translocation of chromosome 21

Question 21

retroviruses

Answer 21

inset their DNA into the host genome, viral DNA can remain there

Question 22

Transposons

Answer 22

aka transposable elements, insert themselves into genes and cause mutations

Question 23

spontaneous mutations

Answer 23

happen with no outside influence by many mechanisms

Question 24

mistakes during replication

Answer 24

more likely if the template base has undergone spontaneous chem arrangement

Question 25

bases can exist in diff forms

Answer 25

one form is rare (tautomers)
if base forms rare tautomer, can pair w wrong base resulting in mismatch pair
if mismatch repaired incorrectly or replicated before repair, causes point mutation

Question 26

chem reactions can alter bases

Answer 26

ex: loss amino group (deamination)

Question 27

meiotic errors

Answer 27

nondisjunction & random breaking and rejoining of chromosomes

Question 28

induced mutation

Answer 28

agent from outside cell causing change in DNA

Question 29

Mechanisms of induced mutation

Answer 29

chem mutagens can alter bases
some chemicals add other groups to bases
Radiation damages DNA

Question 30

about 80% DNA damage can be repaired

Question 31

some bases pairs more vulnerable than others

Answer 31

cytosine often methylated at 5’ position. If 5 meth loses amino acid, becomes thymine

Question 32

mutations have benefits

Answer 32

provide genetic diversity for nat selection
mutations in somatic cells may benefit an organism immediately
mutations in germ lines may cause advantageous change in offspring’s phenotype

Question 33

Gene duplication through transposons not always bad, is a source of genetic variation

Answer 33

one gene may continue in its og role and other my get a gain of function mutation

Question 34

in genes whose products are needed for normal cell processes, mutations are often deleterious esp in germ line cells

Answer 34

somatic cell mutations can also be harmful

Question 35

mutations can be expressed phenotypically as proteins

Question 36

things implicated in genetic diseases

Answer 36

abnormalities in: enzymes, receptor, transport, and structural proteins

Question 37

Loss of enzyme function: phenylketonuria

Answer 37

results from abnormal enzyme, phenylalanine hydroxylase which normally catalyzes the conversion of dietary phenylalanine to tyrosine
loss of enzyme function causes accumulation of phenylalanine phenylpyruvic

Question 38

sickle-cell disease

Answer 38

one amino acid in the beta-globin polypeptide is abnormal
The abnormal protein results in sickle-shaped cells that block capillaries and impair the ability to carry oxygen

Question 39

large deletions

Answer 39

deletions in the X chromosome that include the gene for the muscle protein dystrophin result in Duchenne muscular dystrophy
sometimes only part of gene is missing leading to partly functional protein

Question 40

Chromosomal abnormalities

Answer 40

Gain / loss of complete chromosomes (aka aneuploidy) or segments
Fragile X syndrome is the Restriction in tip of X chromosome resulting in intellectual disability

Question 41

Expanding triplet repeats

Answer 41

gene responsible for fragile X syndrome has repeated triplet, CGG, in promoter region
Usually repeat 6 to 54 times in normal people, 200 to 2,000 times in people with fragile X

Question 42

Somatic cells and cancer

Answer 42

Mutations in them can lead to cancer, more than two are usually needed
Three tumor suppressor genes and one oncogene must be mutated in sequence

Question 43

Many phenotypes are multifactorial

Answer 43

Caused by interactions of many genes and proteins with one or more factors in environment

Question 44

Molecular genetic methods for detecting mutations

Answer 44

Restriction enzymes are when bacteriophages inject DNA into host bacteria cell causing cell to produce more virus particles
Bacteria defenses include restriction enzymes cutting DNA into smaller non-infectious fragments

Question 45

More on restriction enzymes

Answer 45

Each type of restriction enzyme Cuts DNA at specific sequence: restriction site or recognition sequence
Bacterial restriction enzymes can be isolated and used to identify DNA sequences of other organisms

Question 46

Restriction sites

Answer 46

If DNA from any organism is incubated into with restriction enzyme, DNA will be cut wherever restriction site occurs
DNA fragments must be separated to identify where cuts made
Reaction sites are not at regular intervals, so fragments are different sizes and can be separated by gel electrophoresis

Question 47

Gel electrophoresis gives 3 types of info

Answer 47

Number of fragments, how many times recognition sequence occurs in Sample
sizes of fragments
relative abundance of fragments

Question 48

DNA fingerprinting

Answer 48

Uses restriction digestion and gel electrophoresis to identify individuals based on differences in DNA sequences

Question 49

Types of polymorphisms used #1: Single nucleotide polymorphisms

Answer 49

inherited variations in a single base (point mutation)

If SNP occurs in restriction enzyme recognition site, and enzymes don’t recognize one variant, individuals can be distinguished

Question 50

Types of polymorphisms used #2: Short tandem repeats

Answer 50

Short repetitive sequences, usually a non-coding regions that are inherited

Polymerase chain reactions are used to amplify fragments containing short tandem repeats. fragment lengths are different and can be separated by gel electrophoresis

FBI uses 13 of these repeats loci and combined DNA index system, probability that people have the same of these 13 is small

Question 51

Genetic markers

Answer 51

Reference points for Gene isolation. Linkage analysis allows genes to be identified
STRs & SNPs are types

Question 52

Genetic screening

Answer 52

Test to determine if person has genetic disease, predisposed, or is a carrier
Ex: Prenatal screening, screening of newborns, screening of asymptomatic people who have relatives with genetic diseases
Screening may involve analysis for abnormal protein function

Question 53

DNA testing

Answer 53

Direct analysis of DNA for mutations, the most accurate way to detect abnormal alleles
Any cell and body can be analyzed and PCR amplification means only few cells are needed
Testing can be done on cells from embryos or various fetal stages

Question 54

DNA hybridization

Answer 54

Used to detect mutations
PCR amplifies regions where sequence might occur
A short synthetic DNA strand called oligonucleotide probe labeled and hybridized with denatured PCR products