Genetics Flashcards
Sex linked recessive :
color blind, hemophilia, muscular dystrophy
autosomal dominant disease
huntington’s
Autosomal dominant tipoff
affected individual has affected parent.
’failure of penetrance’
dominant gene does not express. often happens with syndactyly in parents and then it expresses in child
X-linked dominant example
CGH- hypertrichosis- lots of extra hair on your face- expresses in all the females.
- Characteristic feature of x-linked recessive; expressed more frequently in boys b/c they are____ meaning that _____
hemizygous. if they had a copy of the bad gene, it is not masked by Y, always expressed
atavistic trait
ancestral trait. ex: hair on face, tails
only possibly Y-linked trait
hairy ears.
If more males in a pedigree, the gene inheritance pattern is probably ___ , and recessive. More females- probably ___. Same: probably autosomal
sex-linked
x-linked dominant
if individuals do NOT have affected parents, disease is :
Autosomal recessive
Linked genes
on the same chromosomes. Linkage group: all these genes located on the same chromosomes. affected in crossing over.
phenylketonuria:
missing the enzyme that normally converts phenylalanine to tyrosine- > autosomal recessive disorder -> damage to developing brain-> metabolites spill over into urine. Infants severely mentally retarded ,often die. If you catch it early enough , put them on a phenylalanine free diet, they develop normally. After their brain finishes developing as an adult, they can eat anything. all newborns in the US are screened for PKU.
Achondroplastic dwarfism
- achondroplastic dwarfism is dominant and the most common types of dwarfism.
Primordial dwarfism
7 lb woman
give examples of common dominant genetic traits you’ll see around the classroom
- Widow’s peak: dominant
- Freckles: dominant
- Dimples: dominant
- Brachydactyly:
short stubby fingers + intellectual challenges. Autosomal dominant
Polydactyly:
more than 5 fingers. Classic 6th finger pointing off of pinky.
Marfan syndrome
connective tissue problem. Causes problems with collagen deposits in cells, connective tissue in aorta wall. If you have it, aorta will become really stretched out, so sometimes the walls of your aorta burst unexpectedly.
People normally tall, thin, super long fingers.
When genes are found on different chromosomes or far apart on the same chromosome, they assort independently and are said to be ___
unlinked
When genes are close together on the same chromosome, they are said to be linked. That means that:
the alleles, or gene versions, already together on one chromosome will be inherited as a unit more frequently than not.
how can recombination frequency be useful to us?
shows us if genes are linked
linkage maps
show the order and relative distances of the genes on the chromosome.
When genes are linked, genetic crosses involving those genes will lead to:
ratios of gametes (egg and sperm) and offspring types that are not what we’d predict from Mendel’s law of independent assortment.
When genes are on the same chromosome but very far apart, they assort independently due to
crossing over (homologous recombination).
what exactly does the linkage mean during crossing over?
Instead of assorting independently, the genes tend to “stick together” during meiosis.
Recombinant
new formation of genes that was not present in the original parents
Parental type
combinations of genes that are identical to what one of the parents were
Why are the recombinant gamete types rare?
crossovers between two genes that are close together are not very common
which will happen more frequently: crossovers between genes close together or spaced further apart?
further apart
T/F: recombination frequency is a direct measure of distane apt on the gene
false. we can say that a pair of genes with a larger recombination frequency are likely farther apart, while a pair with a smaller recombination frequency are likely closer together together.
at what recombination frequency can we say genes are not linked?
50%
does protein carry any genetic information?
no- only DNA does
what experiment was Acetabularia?
exchanged caps between individuals from two species, A. mediterranea and A. crenulata.
After the exchange, each transplanted cap gradually changed from its original form to the form typical for the species of the base it was now attached to. This showed that the nucleus controlled the form of the cap.
Griffith-Avery experiment
- 2 types of bacteria. One ‘s’ strain kills mice. R strain does not.
- Took some S strain, heat it up and kill it- mice live.
- Some heat killed smooth ones + rough ones: mice die! Some factor that comes from the heat killed ones and transforms the R’s into S’s.
- Griffith coined the term ‘the transforming factor.’ Some bacteria can take up naked DNA (transformation in bacteria!)
Avery, MacLeod & McCarty
took cultures of heat-killed S cells and progressively purified the transforming principle by washing away, separating out, or enzymatically destroying the other cellular components.
hypothesis: genetic material of cell is either protein or DNA
conclusion: transformation requires DNA therefore it is genetic material of cell
Hershey and Chase experiment
used bacteriophage, or viruses that attack bacteria, inject cells.
- S35 to label proteins (only found in meth, cysteine)
- P32 Phosphorous to label DNA (only found in DNA)
concluded that DNA, not protein, was injected into host cells- only see phosphorus in pellet- and made up the genetic material of the phage.
to which end of DNA is the new strand added?
Nucleotides ALWAYS ADDED AT 3’ end of original strand
T/F: eukaryotes have more than one replication origin?
True
draw a replication DNA strand. label ends and bubble.
leading strand 5’- 3’
lagging strand 3’-5’
2 bidirectional ORI’s at replication fork
how did the 2nd avery validate the work of griffith avery?
proved that the transforming factor = DNA
what happens in S phase?
synthesizing strands of dna, bidirectionally. eventually these bubbles fuse and separate giving u 2 new strands
are dna visible in s phase
no! only in prophase
Semi conservative model
each parental strand becomes a new strand
Meselson + Stahl experiment to prove semi conservative
incorporate heavy nitrogen into DNA. use cesium chloride to create a density gradient, and centrifuge. know that light DNA will float on top (Cs on bottom) , ‘intermediate’ DNA floats in middle, pure heavy DNA sinks to bottom . F1 generation floats in middle- proves 1 heavy strand 1 light strand DNA aka semiconservative
Replication origin- how does this initiate the process of replication?
A specific DNA sequence (usually rich in ?) which is recognized by proteins involved in initiating DNA replication
Typically, this process begins with the binding of an “initiator” protein to a specific DNA sequence or “replicator.” In response to the appropriate cellular signals, the initiator directs a local unwinding of the DNA double helix and recruits additional factors to initiate the process of DNA replication
Replicon:
The length of DNA replicated from a single origin
DNA Polymerase
enzymes that create DNA molecules by assembling nucleotides, the building blocks of DNA. These enzymes are essential to DNA replication and usually work in pairs to create two identical DNA strands from one original DNA molecule.
what 4 things do dna polymerases require?
- Unpaired base in DNA template strand
- Free 3’ end on growing strand – i.e. a “primer”
- A deoxynucleoside triphosphate (dCTP)
- Mg++ ions
deoxyribonucleoside triphosphate’
nucleotide precursor
where do you obtain the energy to assemble DNA for dna polymerase to use?
2 Phosphates in double form: pyrophosphate. Tends to fall apart into 2 inorganic phosphates. Helps to keep equilibrium constant further to synthesis side of the equation. High energy linkage between 2 phosphates at 3’ end of primer strand is what is used to make rxn happen.
Describe DNA polymerase enzyme proofreading activity
proofreads 3’->5’ :
- if DNA messes up and polymerase adds an incorrect nucleotide, cuts it out throws it away and tries again. ‘high fidelity’ aka hardly makes any mistakes.
- ‘3-5’ exonuclease’
what are the 2 separate domains of DNA polymerase
- Polymerization domain
- Editing domain
recall that domains are functional regions
how is the DNA helix opened to begin replication?
initiator proteins
Genes D, E, F, and G are located on the same chromosome. The distances between the genes are below:
Relationship Map Unit Distance
G - D 11
G - E 7
G - F 22
E - F 15
D - E 4
What is the order of the genes on the chromosome?
GEDF
pseudoautosomal regions
area of Y chromosome that recombines
adrenal hyperplasia
cortisol synthesis defect .
Symptoms in infants may include ambiguous genitalia in girls and an enlarged penis in boys.
Turner syndrome
XO in females
Gart gene
leads to high level of blood purines, many think this can cause mental retardation esp in down syndrome
aneuploidy
excess of multiple chromosomes
non-disjunction
chromosomes fail 2 separate during meiosis. if sex chromosomes, could have huge results (sex chromes have thousands of genes) - kid often dies
non-disjunction on autosome examples
down syndrome, patav syndrome. still born, huge defects
triploid
3 copies of ALL genes
non disjunction in sex chromosomes leads to what diseases?
XO (turners) XXX, XYY, XXY (klinefleter)
give an example of a deoxyribonucleoside triphosphate group
- : dCTP, dATP, dGTP, dTTP
what does the dehydration synthesis on the DNA polymerase with the incoming phosphate group?
the free 3’ hydroxyl group
describe lagging strand synthesis
lagging strand runs 3’ to 5’; because of this, DNA polymerase requires there to be an RNA primer so it has a 3’ end to hook onto. it builds slower and has okazaki fragments
what does it mean when we say DNA polymerase III cannot start de novo?
cant start putting in bases if there’s no 3’ end to hook it to.
how does the DNA keep building when faced with lagging strand
- enzye DNA primase creates RNA primer in 5’-3’ direction
- DNA polymerase adds to new RNA primer to start new okazaki fragment.
- DNA polymerase finishes fragment, old RNA primer erased and replaced by DNA.
- 2 new pieces of DNA Sealed together by DNA ligase
Okazaki fragments:
DNA strands with little bits of RNA attached to them
average length of okazaki fragments
5 nucleotides long
Initiator Proteins
Initiator proteins recognize origin sites and pulls the DNA strands apart to start the process of replication
DNA helicase
unzips genes
how long of a gap do you need on the parent strand to initiate replication?
a gap of 3,000 nucleotides
dna polymerase I
sees the rna and edits out the RNA . chews off and extends the end of the last piece of DNA, runs it to the new piece of DNA
DNA ligase
seals the gap between DNA strands during synthesis of new strand via lagging strand mechanism
Dna primase
synthesizes RNA primer
- “leading strand is extending the ___, lagging strand extends itself by ____’
3’ end, okazaki fragments
- DNA gyrase
relieves torque. aka, untangles things
T/F: humans have exactly the same enzymes as bacteria
true! serves as additional evidence of common ancestor
Telomere end replication:
Telomerase enzyme uses its RNA as a template to prime the synthesis of DNA back in the other direction. It adds additional repeating units to the template strand . Then, the DNA synthesis (using RNA primer) completes the lagging strand.
where would you expect to see telomerase
- Happens a lot in stem cells
- Not every cell has telomerase enzyme.
why can telomerase enzymes be considered a form of reverse transcriptase?
telomerase enzyme mirrors a dNA polymerase except that it uses rna as a template. its essentially the exact way dna forms RNA, just going in the reverse
Reverse transcriptase:
- A DNA polymerase that uses RNA as a template.
ex of reverse transcriptase
HIV virus:
- Virus enters into cell. Protein envelope falls off. Genomic material comes out (inside cell).
- polymerase copies the RNA sequence into a dna and then back the other way, to make a double stranded DNA out of the original RNA.
- Then that DNA it just copied gets inserted into genomic DNA of host cell, copied into RNA, makes proteins, makes new viruses- turns cell into virus production factory.
why is reverse transcriptase rare and unique
usually we go from DNA -> RNA, as DNA is more stable
normal flow of information in genetic material going to proteins:
- normal flow of info: DNA -> rna-> protein
transcription
copy info from DNA into an RNA copy. DNA is the master copy, RNA is ‘working copy
transcription vs translation
- Translation produces the proteins.
- Transcription produces RNA.
Messenger RNA
codes for protein- brings the message of what sequence is needed
Ribosomal rna
rRNA. help make up ribosomes. Come in various sizes- always a big one and a small one. 16S, 23S are the sizes in prokaryotes, and 18S, 28S in eukaryotes .
Transfer RNA:
Carries amino acids over to ribosomes when preparing to make proteins
how do prokaryotes differ in their varieties of rna?
use a single type of RNA polymerase to transcribe all types of RNA’s
Transcription
a segment of DNA is copied into RNA by the enzyme RNA polymerase
RNA polymerase vs DNA polymerase : 5 differences
RNA polymerase: no primer required, . NTP’s instead of deoxyntp’s. DNA is template instead of RNA. no helicase (unzips itself.) no editing function.
name some factors that cause allelic frequencies to change
non random mating. random gentic drift. migration. artificial selection (environement changes). mutation
