genetics final exam Flashcards
gene linkage
when two or more genes located on the same chromosome are so close that their alleles are unable to assort independently
recombinant genes
different from parental genotypes; crossing over occurred
parental genes
same as parental genotype; no crossing over
how do you know if there is gene linkage?
if the parental genotypes are the most frequent in the progeny
how do you know if there is no genetic linkage?
if gametes occur in a 1:1:1:1 ratio.
complete genetic linkage vs incomplete genetic linkage?
Complete: ONLY parental gametes observed
Incomplete: parental and recombinant gametes are observed in the progeny
what increases the chances of crossing over?
greater length apart on a chromosome (further apart = increased chance of crossing over)
steps in constructing a gene map?
- identify the progeny classes (parental; most frequent, double cross overs; least frequent, single cross overs)
- determine gene order by comparing parental to double crossovers
- determine distance between each gene by calculating recombination frequency
- calculate coefficient of coincidence and interference
what kind of bonds are nucleotides joined by in DNA?
covalent phosphodiester bonds
what type of bonds are nucleotide pairs held together by?
How many bonds between each?
hydrogen bonds
-A to T: 2
-G to C: 3
what are the three components of nucleotides?
- A deoxyribose sugar
- one of four nitrogenous bases
- up to three phosphate groups
what are the two shapes of nitrogenous bases?
Pyrimidine, purine
Pyrimidine
Single ringed bases.
Includes cytosine and thymine (one six-ringed structure)
Purine
Double-ringed bases.
Included adenine and guanine (six ring and five ringed structure)
Meselson-Stahl experiment
Used to decipher the mechanism of DNA replication
Method to meselson-stahl experiment?
-tube is filled with CsCl and subjected to high ultracentrifuge speeds, separating them and creating a density gradient
-the parental strands contain N^15 nitrogen duplexes, which are mixed with an N^14 duplex.
-the density gradient shows how these isotopes are dispersed
what are the three models created by the meselson-stahl experiment? which one is accepted?
conservative, semiconservative, and dispersive replication
-semiconservative is accepted (each progeny retains one parental strand)
where is DNA replication initiated ?
at a DNA sequence called the replicator
-includes the origin of replication (region where double helix denatures)
how long does DNA replication take in humans?
over an hour (at 50 base pairs per second)
What are the enzymes involved in DNA replication? (8)
-histones
-DNA topisomerase
-DNA helicase
-single stranded binding protein (SSB)
-primase
-DNA polymerase III
-DNA polymerase I
-DNA ligase
histones
responsible for supercoiling of DNA
DNA topoisomerase
relaxes supercoiling of DNA during replication
DNA helicase
unwinds the double helix during replication
-recruits DNA primase
single standed binding protein (SSB)
binds to single stranded DNA to stabilize it and prevent re-annealing
primase
synthesizes RNA primers (substrates for DNA polymerase III)
DNA polymerase III
synthesizes daughter strands (adds new nucleotides)
-complete in leading strand, incomplete in lagging
DNA polymerase I
removes + replaces RNA primer with DNA
DNA ligase
joins the Okazaki fragments
which direction is DNA synthesized in?
5’ to 3’
-template strand is 3’ to 5’
End replication problem (telomeres)
-linear chromosomes are unable to replicate right to their ends. Therefore, they get progressively shorter with each replication cycle
-issue is resolved by the presence of hundreds to thousands of telomeres at the end of chromosomes
-telomeres do not contain protein-coding genes
-chromosome shorting occurs in most somatic cells but not germ cells
Polymerase chain reaction (PCR)
automated version of DNA replication
-also known as “amplification”; product known as “amplified DNA”
what does PCR require?
- double stranded DNA template (to be copied)
- DNA nucleotides (dNTPs)
- DNA polymerase (heat stable; called Taq polymerase)
- DNA primers (single stranded)
- a buffer solution
how many cycles is ran during PCR?
-30-35 cycles
-each double the number of copies of the targeted DNA sequence
what are the steps of PCR?
- denaturation (mixture is heated to 94ºC, causing DNA to denature into single strands. Takes roughly 1 minute)
- Annealing: temp is reduced to 54ºC to allow for primer annealing. Takes roughly 45 seconds.
- Extension: temp is raised to 72ºC to allow for primer extension, during which Taq polymerase synthesizes the DNA. Takes roughly 2 minutes.
automated DNA sequencing
each nucleotide is labelled with a fluorescent marker
-then used with gel electrophoresis to separate DNA fragments
Agarose gel electrophoresis
method for separating different protein/nucleic acid molecules/fragments from one another using an electric field
-charge is applied which separate the molecules based on charge, shape, and size.
what are the steps of gel electrophoresis?
- pour agarose gel into the plastic casting tray
- allow gel to solidify
- remove comb; wells are left in the gel
- remove gel from casting tray, place in a buffered solution with electrodes
- add biological samples to wells, apply currents. Samples migrate towards the positive charge.
Sanger sequencing
-also known as dideoxynucleotide DNA sequencing
-used to determine DNA sequences
process of sanger sequencing?
-small amounts of dideoxynucleotide triphosphate (ddNTP) is added to large amounts of the four standard dexoynucleotides (dNTP) of DNA (A,T,G,C)
-after the reactions, the components of each reaction are loaded into separate lanes of a DNA gel electrophoresis gel
-components are separated by length
-DNA fragments towards bottom of gel are shorter than those higher up
how is the product of sanger sequencing read?
Read from the bottom (5’) to the top (3’).
how is RNA different from DNA?
- has a ribose sugar instead of deoxyribose
- usually single stranded
- Uracil instead of Thymine
what are the five types of RNA?
- messenger RNA (mRNA)
- Transfer RNA (tRNA)
- Ribosomal RNA (rRNA)
- Small nuclear RNA (snRNA)
- Micro RNA (miRNA)
messenger RNA
encodes amino acid sequence
-short lived, intermediary between DNA and protein
-only type of RNA that undergoes translation
ribosomal RNA
makes up ribosomes with ribosomal proteins
transfer RNA
brings amino acids to ribosomes during translation
-each bind to a specific aa
-at 3’ ends, all have: 5’—–
small nuclear RNA
makes complexes (and proteins) that are used in RNA processing
micro RNA
involved in post-transcriptional regulation of DNA
small interacting RNA (siRNA)
protects plants and animals from production of viruses and movement of transposons
what are the two steps of protein coding?
- transcription (DNA –> RNA)
- translation (RNA –> protein)
transcription
transfer of genetic information from double stranded DNA template into single stranded RNA
translation
conversion of RNA base sequence info into amino acid sequence of a polypeptide
gene expression
the base pair sequences that are being transcribed (only some DNA transcribed at a time)
gene regulatory elements
base pair sequences associated with each gene that are involved with its expression
template, RNA, and nontemplate strands of RNA synthesis
template stand: 3’ to 5’ DNA strand
RNA: 5’ to 3’ RNA strand made from template DNA
nontemplate: 5’ to 3’ complementary DNA strand. Same polarity as RNA.
steps of transcription
- the RNA polymerase core enzyme and sigma subunit bind to -10 and -35 promoter consensus sequence
- DNA unwinds near the transcription site to form the open promoter complex
- RNA polymerase holoenzyme initiates transcription and begins RNA synthesis
- Core enzyme synthesizes until it reaches a termination sequence
- transcription terminates, the core enzyme + RNA transcript are released
where does transcription and translation occur in eukaryotes? Prokaryotes?
Eukaryotes: transcription in nucleus, translation in cytoplasm
Prokaryotes: both occur in cytoplasm
what are the three sequences protein coding genes are made up of?
- promoter: starting point for transcription
- RNA coding sequence: codes for single stranded mRNA
- Terminator: ending point of transcription
cloverleaf model of tRNA
-complementary base-pairing between different sections of the tRNA molecules form 4 base-pair stems separated by four loops (I, II, III, IV).
-loop II contains the anticodon which pairs with a codon during translation, and ensures correct amino acid sequencing
what are the three steps in translation?
- initiation
- elongation
- termination
what are the two main types of mutations?
- point/base pair mutations
- chromosomal mutations
point mutations
mutations which substitute, add, or delete one or more DNA base pairs
-occur at a specific, identifiable position in the gene or genome
types of point mutations?
- base-pair substitution mutations
- transition mutations
- transversion mutations
base pair substitution mutations
the replacement of one or more nucleotide base pairs
-three types: synonymous mutations, missense mutations, nonsense mutations
transition mutations
one purine replaces another, or one pyrimidine replaces another
transversion mutation
one pyrimidine replaces a purine, or vice versa
synonymous mutation
a base pair change that does not alter the resulting amino acid (codes for the same protein)
missense mutation
a base pair change that results in a different amino acid (new protein is made)
nonsense mutation
creates a pre-mature stop codon
frameshift mutation
insertion or deletion of one or more basepairs, causing the entire sequence to shift
chromosomal mutations
mutations which change the number or structure of chromosomes
types of chromosomal mutations
- structure (deletion, duplication, inversion, translocation)
- number (aneuploidy, euploidy)
structure chromosomal mutations
caused by one or more breaks in chromosomes
-types: deletions, duplications, inversions, translocations
deletion structural chromosomal mutations
involves the loss of a chromosomal segment
-causes: heat, radiation, viruses, chemicals
-consequences depend on which genes/parts are lost
-may cause recessive disorders to be expressed if the dominant allele is lost
duplication structural chromosomal mutations
involves the doubling of a segment of chromosome
inversion structural chromosomal mutations
no change in the amount of DNA, but changes the arrangement of a chromosomal segment
-two types: pericentric inversion, paracentric inversion
Piericentric inversion vs Paracentric inversion
Piericentric: includes centromere
Paracentric: does not include centromere
translocation structural chromosomal mutations
change in the location of one or more DNA segments
-sometimes the cause of tumours
number chromosomal mutations types
aneuploidy, euploidy
Aneuploidy
one or more chromosomes added/removed from a normal set
-usually lethal in animals
Trisomy, example
A form of aneuploidy when an n+1 gamete is fertilized by an n gamete
-ex: trisomy 21 (3 copies of chromosome 21)
euploidy
involves changes in complete sets of chromosomes
-results from nondisjunction during meiosis
-lethal for most animals
polyploids
organisms with more than two basic sets of chromosomes
-3x: triploid
-4x: tetraploid
-5x: pentaploid
-6x: hexaploid
-ex: wheat. x=7, 2n=6x=42.
monoploids
arise spontaneously in natural populations
-found in males of some wasps, bees, ants, etc.
how many lethal gametes does nondisjunction of meiosis I result in? meiosis II?
meiosis I: two lethal gametes
meiosis II: one lethal gamete
what are the types of polyploidy in plants?
- autopolyploids
- allopolyploids
autopolyploid
composed of multiple sets of chromosomes from ONE species
-arise from duplication of existing genomes within the organism
allopolyploid
composed of multiple sets of chromosomes from DIFFERENT species (inbreds)
-organism with one haploid (n) set of each parent’s chromosomes, then doubled
