Genetics Exam Ii

Front 1

What violates Mendel's first law of segregation?

Back 1

non-disjunction

Front 2

What violates Mendel's second law of independent assortment?

Back 2

recombination

Front 3

Human leukocyte antigen is an example of which concept?

Back 3

multiple alleles

Front 4

partial (or incomplete) dominance

Back 4

the condition resulting when one allele is not completely dominant to another allele so that the heterozygote has a phenotype between that shown in individuals homozygous for either individual allele involved

Front 5

codominance

Back 5

the situation in which the heterozygote exhibits the phenotypes of both homozygotes

Front 6

expressivity

Back 6

the degree to which a particular genotype is expressed in the phenotype (i.e. polydactylism in cats)

Front 7

penetrance

Back 7

the frequency with which a dominant or homozygous recessive gene manifests itself in the phenotype of an individual (i.e. hemochromatosis)

Front 8

pleiotropy

Back 8

multiple phenotypic effects resulting from a single mutant gene (i.e. cystic fibrosis)

Front 9

polygenic traits

Back 9

traits encoded by many loci

Front 10

epistasis

Back 10

one gene “masks” or alters the expression of another

Front 11

recessive epistasis

Back 11

conceptually, one enzyme’s function leads to the formation of another enzyme’s substrate (i.e. flower color, 9:3:4)

Front 12

duplicate recessive epistasis

Back 12

homozygous recessives at either of two genes produce the same phenotype as the homozygous recessive for both genes (i.e. flower color in sweet peas, 9:7)

Front 13

duplicate dominant epistasis

Back 13

both genes need to be mutant for recessive phenotype (i.e. ovoid or triangular leaf shape, 15:1)

Front 14

dominant epistasis

Back 14

the dominant allele at one trait is sufficient to produce the dominant phenotype (i.e. color in squash, 12:3:1)

Front 15

lethal allele

Back 15

an allele that results in the death of an organism (i.e. yellow gene in mice, 2:1)

Front 16

conditional mutant

Back 16

a mutant organism that is normal under one set of conditions but becomes seriously impaired or dies under other conditions (i.e. neurotransmitter gene in flies and colors in Himalayan rabbits)

Front 17

central dogma of molecular biology

Back 17

DNA replicates and is transcribed into RNA, which is translated into protein

Front 18

gene

Back 18

a region of DNA that is necessary to encode an RNA molecule and is passed from parent to offspring and is capable of change (mutation- recombination)

Front 19

transcription

Back 19

the transfer of information from a double-stranded DNA molecule to a single-stranded RNA molecule

Front 20

promoter

Back 20

a specific regulatory nucleotide sequence in the DNA to which RNA polymerase binds for the initiation of transcription

Front 21

What are the two sites in bacterial transcription initiation promoter?

Back 21

-35 and -10

Front 22

-35 consensus sequence

Back 22

TTGACA

Front 23

-10 Pribnow box consensus sequence

Back 23

TATAAT

Front 24

What is the RNA holoenzyme made up of?

Back 24

RNA polymerase (two a, a b and a b’ subunits) + sigma factor

Front 25

Which species of eukaryotic RNA do these polymerases transcribe?
RNA polymerase I
RNA polymerase II
RNA polymerase III

Back 25

RNA polymerase I- rRNA
RNA polymerase II- mRNA and snRNA
RNA polymerase III- tRNA

Front 26

Which box is located in the eukaryotic promoter region at approximately -25?

Back 26

TATA box (TATAAA consensus sequence)

Front 27

Which eukaryotic promoter consensus sequence is located at about -75?

Back 27

CAAT box

Front 28

Which eukaryotic promoter consensus sequence is located at about -90?

Back 28

GC box (consensus sequence GGGCGG)

Front 29

What are three structural motifs of transcription factors?

Back 29

basic helix loop helix (BHLH), leucine zipper, zinc finger

Front 30

What are the events that occur during the initiation of transcription in eukaryotes?

Back 30

TBP binds to TATA box. TAF binds to TBP to become TFIID. Dimer of TFIIA and TFIIB binds. RNA polymerase can then bind. TFIIF, TFIIE, TFIIH, and probably many others stabilize this.

Front 31

elongation

Back 31

RNA polymerase “reads” the template strand and puts in the corresponding rNTP

Front 32

prokaryotic rho dependent termination

Back 32

rho is a protein that unwinds the DNA-RNA heteroduplex; it finally catches up to the polymerase and when it does, it destabilizes the RNA polymerase holoenzyme

Front 33

prokaryotic rho independent termination

Back 33

usually a secondary structure called a hairpin in the RNA destabilizes the RNA polymerase binding

Front 34

What is a 5' cap?

Back 34

When eukaryotic pre-mRNA is 20 to 30 nucleotides long, a capping enzyme adds 7-methyl guanosine to the 5' end, forming a 5'-5' linkage.

Front 35

What is the purpose of the 5' cap and 3' polyadenylation?

Back 35

They are recognition factors for nuclear export, and they increase the longevity of the molecule by protecting against RNAses.

Front 36

How is eukaryotic pre-mRNA trascription terminated?

Back 36

Elongation continues thousands of base pairs past a polyadenylation site, which is a consensus sequence of AAUAAA. CPSF (cleavage and polyadenylation specificity factor) binds to AAUAAA sequence. CstF binds to a GU/U region as well as to CPSF, forming loop in pre-mRNA. CFI and CFII bind to and cleave RNA. Once RNA is cut, PAP (poly A polymerase) puts in a variable length of adenine.

Front 37

What is the consensus sequence that defines a splice site?

Back 37

5' GU......YNCURAY......AG 3'
(Y=pyrimidine, R=purine, N=any nucleotide)

Front 38

What is a snRNP?

Back 38

small nuclear ribonucleoprotein

Front 39

What are the events involved in splicing?

Back 39

U1 binds to 5' splice site. U2 binds to A in branch point sequence. U4/U6 binds to U5, which binds to U1 and U2, forming a loop. U4 leaves. This is an active spliceosome and splicing occurs. Intron released in lariet shape with snRNPs.

Front 40

What's the purpose of splicing?

Back 40

Different forms of the same/similar protein can be formed with the same gene. Specific biochemical properties of proteins can be regulated.

Front 41

What is the benefit of RNA editing?

Back 41

It is a mechanism to increase the number of different proteins available without the need to increase the number of genes in the genome. It may protect the genome against some viruses. It also may allow for intramolecular base pairing to form double-stranded RNA.

Front 42

How many different amino acids are there?

Back 42

20

Front 43

What is the basic structure of an amino acid?

Back 43

An amino group, an R group, and a carboxyl group.

Front 44

zwitterion

Back 44

an ion that has both a positive and negative charge

Front 45

What kind of bonds to amino acids form to each other?

Back 45

peptide bonds

Front 46

What are the four levels of structural arrangments in proteins?

Back 46

primary- amino acid sequence
secondary- regular folding and twisting of single polypeptide chain like a-helices and b-pleated sheets
tertiary- three-dimensional structure caused by folding
quaternary- complex of polypeptide chains in a multisubunit protein

Front 47

molecular chaperones

Back 47

proteins which function to keep other proteins in the correct conformation/structure

Front 48

Where are ribosomes located?

Back 48

in the cytoplasm or associated with the endoplasmic reticulum

Front 49

aminoacyl-tRNA synthetase

Back 49

charges amino acid with tRNA

Front 50

How many different aminoacyl-tRNA synthetases are there?

Back 50

20

Front 51

What are the events of protein synthethis in prokaryotes?

Back 51

Initiation factors bind to 30S ribosomal subunit. 30S binds to Shine-Dalgarno sequence and AUG initiation codon. Initiator tRNA binds to start codon. Initiation factors dissociate, and GTP is hydrolyzed. 50S subunit is attached.

Front 52

elongation in translation

Back 52

addition of amino acids to the growing polypeptide chain

Front 53

p site

Back 53

peptidyl site of the ribosome where start codon-anticodon is bound

Front 54

Ef-Tu

Back 54

elongation factor Tu with GTP binds to next aminoacyl-tRNA molecule in the A (aminoacyl) site of the ribosome

Front 55

peptidyl transferase

Back 55

forms peptide bond between between freed peptide from P site and amino acid in A site

Front 56

translocation

Back 56

dissocation of Ef-Tu and GTP ratchets the ribosome forward, making the A site the P site

Front 57

What are the events of translation termination?

Back 57

Release factors and unspecified tRNAs recognize stop codon. Polypeptide is released from tRNA at P site, tRNA is released from ribosome, and ribosome dissociates.

Front 58

wobble hypothesis

Back 58

a theory proposed by Francis Crick which proposes that the base at the 5' end of the anticodon (3' end of the codon) is not as constrained as the other two bases; this feature allows for less exact base pairing so that the 5' end of the anticodon can potentially pair with one of three different bases at the 3' end of the codon

Front 59

somatic mutation

Back 59

mutation in a somatic cell that can harm the individual

Front 60

germline mutation

Back 60

mutation that occurs in a germ cell, which won't really harm the individual but will be passed on to offspring

Front 61

point mutations

Back 61

a mutation caused by a substitution of one base pair for another

Front 62

transition mutation

Back 62

a specific type of base-pair substitution mutation that involves a change in the DNA from one purine-pyrimidine base pair to the other purine-pyrimidine base pair at a particular site (i.e. AT to GC)

Front 63

transversion mutation

Back 63

a specific type of base-pair substitution mutation that involves a change in the DNA from a purine-pyrimidine base pair to a pyrimidine-purine base pair at the same site (i.e. AT to TA or GC to TA)

Front 64

silent mutation

Back 64

substitution mutation that does not change the amino acid the codon is coding

Front 65

missense mutation

Back 65

changes the identity of a single amino acid; may or may not impact the function of the protein (conservative amino acid changes versus non-conservative amino acid changes)

Front 66

nonsense mutation

Back 66

changes an amino acid specifying codon into a stop codon; leads to premature termination of the protein

Front 67

frameshift

Back 67

addition or deletion of bases can alter the “reading” frame of the mRNA

Front 68

forward mutation

Back 68

a mutational change from a wild-type allele to a mutant allele

Front 69

reverse mutation

Back 69

a mutational change from a mutant allele back to a wild-type allele

Front 70

suppressor mutation

Back 70

diminishes effects of first mutation by acting at another site

Front 71

intragenic suppressor

Back 71

second mutation occurs within the same gene, could restore proper reading frame

Front 72

intergenic suppressor

Back 72

second mutation within another gene (i.e. Tyr-tRNA mutant reads stop codon in E. coli)

Front 73

spontaneous mutations

Back 73

mutations that occur without the use of chemical or physical mutagenic agents

Front 74

mutation rate

Back 74

probability of a specific type of mutation as a function of time

Front 75

mutation frequency

Back 75

number of occurrences of a mutation as a proportion of cells/individuals in a population

Front 76

tautomeric shift

Back 76

changing from base to tautomer of base allows for abnormal base pairing; tautomers will revert to original form unless bout of replication occurs

Front 77

strand slippage

Back 77

occurs at highly repetitive sequences of DNA, polymerase “slips” and either repeats or deletes bases, usually accompanied by intramolecular base pairing

Front 78

deamination

Back 78

removal of an amino group off a base (if C is methylated and then deaminated, it is converted to T)

Front 79

depurination

Back 79

bond between the purine and deoxyribose breaks; if not repaired prior to replication, no base is specified and a random base is inserted

Front 80

induced mutation

Back 80

mutation that results from treatment with mutagens

Front 81

ultraviolet radiation

Back 81

induces pyrimidine dimers, mostly TT, which are unable to base pair correctly

Front 82

base analogs

Back 82

compounds that are similar in structure to the normal complement of nitrogenous bases and so can be incorporated into the double helix; although they do not behave the same (i.e. 5-bromouracil acting like T)

Front 83

base modifying agent

Back 83

changes the chemistry/behavior of existing bases (i.e. nitrous acid as deaminating agent and EMS and DMS as alkylating agents)

Front 84

intercalatating agent

Back 84

compounds that insert themselves between adjacent nucleotides on the double helix, typically cause frameshifts

Front 85

mutator mutations

Back 85

mutations which increase the overall number of mutations within an organism, affect various DNA repair mechanisms (i.e. mutD affecting DNA Polymerase III, loss of exonuclease activity)

Front 86

photoreactivation

Back 86

one way by which thymine dimers can be repaired; the dimers are reverted directly to the original form by photolyase and exposure to visible light in the wavelength range 320–370 nm

Front 87

excision repair

Back 87

enzymes recognize distortion of helix, endonucleases excises 10-12 bases of helix surrounding distortion, glycosylases remove damaged bases leaving a hole, AP endonucleases cleave phosphodiester bond around missing base, DNA polymerase fills in the missing sequences, ligase reattaches adjacent bases

Front 88

mismatch repair

Back 88

mutS binds to mismatch, recognizing newly synthesized DNA; mutL and mutH excise new strand; DNA polymerase III fixes

Front 89

SOS response

Back 89

severe DNA damage induces this response in E. coli; if there's no damage, lexA represses transcription of about 17 gene involved in DNA repair; damage activates recA protein which cleaves lexA protein; DNA repair genes are transcribed

Front 90

Why isn't SOS response left on all the time?

Back 90

response itself is mutagenic; CG-TA transitions are most common with CC dimers

Front 91

unequal crossing over

Back 91

mechanism that leads to the addition or loss of chromosomal material

Front 92

aneuploidy

Back 92

abnormal condition in which one or more whole chromosomes of a normal set of chromosomes either are missing or are present in more than the usual number of copies

Front 93

What are the consequences of this loss/addition of genetic material?

Back 93

most homozygous deletions lead to lethality, heterozygotes "uncover" the other allele, can be used in deletion gene mapping

Front 94

cri-du-chat syndrome

Back 94

results from observable deletion of part of the short arm of chromosome 5

Front 95

Prader-Willi syndrome

Back 95

results from deletion of part of long arm of chromosome 15; infants weak because sucking reflex is poor, by 5 or 6 they become compulsive eaters and can eat themselves to death

Front 96

What can happen if two breaks occur on the same chromosome?

Back 96

inversions or small deletions

Front 97

inversion

Back 97

a change in the order of genes along a chromosome

Front 98

How does inversion affect alignment in meiosis?

Back 98

leads to the formation of a loop in the inverted chromosome

Front 99

paracentric inversion

Back 99

does not include centromere, forms inviable dicentric and acentric chromosomes

Front 100

pericentric inversion

Back 100

forms monocentric chromosomes, some inviable deletion/duplication products

Front 101

translocation

Back 101

exchange of genetic material between non-homologous chromosomes

Front 102

Robertsonian translocation

Back 102

not reciprocal, involves the fusion of two non-homologous acentric chromosomes

Front 103

mutational hotspots

Back 103

repetitive sequences, AT rich, C methylation, palindromic sequences, transcriptional active spots

Front 104

conditional mutation

Back 104

a mutation which changes a phenotype only under certain environmental conditions

Front 105

How can environmental conditions affect gene expression?

Back 105

Environmental conditions can affect what genes are expressed as well as the amount of expression.

Front 106

Where is the point of major gene expression control?

Back 106

transcriptional regulation- what genes, how many transcripts, where and when

Front 107

cis acting element

Back 107

"same," these are DNA sequences

Front 108

trans acting element

Back 108

"across," proteins encoded by different genes