Genetics Flashcards
wild type vs mutant
Wild-type allele predominates in the natural population, the common one
Mutant alleles are changes from wild-type allele
Mutation can change gene back (revert) to wild-type allele
genotype and phenotype
Genotype = genetic makeup of an organism
Phenotype = the appearance of an organism
Can have same phenotype but a different genotype**
homozygotes and heterzygotes
Humans are diploid (have two copies of each chromosome and each gene) we are diploids meaning we come in pairs! they can be the same as each other or different we can be homo or heterozygous for particular gene
If alleles of a given gene are identical, individual is homozygous (2 of the same alleles)
If alleles of a given gene are different, individual is heterozygous (2 differnet alleles at genetic locus)
Homozygous lines are true-breeding, give rise to identical progeny
what is locus
IT IS A LOCATION**
monohybrid cross
Monohybrid cross = parents are heterozygous for a single gene
mono= one genetic locus capital A, and hybrid because both parents are hetero Aa crossed with Aa
• Example: Aa × Aa
genotype ratio
1: 2:1
1: AA
2: Aa
1: aa
phenotype ratio: 3:1 assuming that big A is completely dominant over little a
dihybrid cross
looking at two different genetic loci, is a dihybrid cross
- Dihybrid cross = parents are heterozygous for two genes
- Example: AaBb × AaBb
to do pend. square 16 cross, each inherited possible gametes from parent number 1 are AB, Ab, aB and ab look on image!
possible gametes from parent number two are the same
square represents all genotypes related to A and B for this organism, in terms of the phenotypes it is possible for the offspring to be dominant for A dominant for B, recessive A dominant for B, domina A recessive b or recessive for both!
so question is if looking at these 16 options how many out of 16 represent dominant of A and dominant for B
generation nomenclature
P = parental generation
F1 = first filial generation
F2 = second filial generation (progeny of F1 intercross)
dominant and recessive alleles
Dominant allele is indicated by capital letters
One copy of a dominant allele is sufficient for phenotype
AA homozygotes and Aa heterozygotes have the same phenotype
Dominant allele masks presence of recessive allele in heterozygote
Recessive allele indicated by lowercase letters
Recessive phenotype only observed in homozygotes (i.e., aa)
genes, alleles and loci
A gene is the unit of biological function
One gene typically produces one protein
Locus is the location of gene on the chromosome
Alleles are variants of a gene
dihybrid cross cont. 2
9:3:3:1
these represent ratio of phenotypes for a dihybrid cross!
if had the question what is the probability that a child will be homozgous recessive have for both traits? parets are heterozygote for both
dihybrid cross 3
(for probablity)
then break it down into different, mnuch smarter when doing problems to break down probability for A then for B
get this 9:3:3:1 when not linked! either on different chromosomes OR very far apart on differnt chromosomes, can conclude there will be a 9:3:3:1 ratio of phenotypes, if observe 9:3:3:1 of phenotype ratios provides evidence that the genes are not linked another way of saying that is they assort indedendently… version allele of A is independent from version of B that gets passed down those are two independent random events
testcross
testcross means organism with dominant phenotype and do not know what its genotype is could be AA or Aa and you want to know which one so cross with homozgous recessive, and then from the results you can see you would be making two possible P squares
Often, one does not know genotype of an organism
Use a test cross to a recessive tester strain
Example: strain has A phenotype, but could be Aa or AA genotype
Test cross to aa strain
If 100% progeny are A phenotype, then parent was AA
If 50% progeny are A phenotype, 50% a phenotype, then parent was Aa
Based on results can figure out if original dominant organism was homoz dominant or heterozygous dominant- results tell you genotype of original dominant organism!!!
backcross
Backcross is crossing progeny to one parent (P × F1)
Repeated backcrossing generates pure inbred lines (e.g., for mice and plants)
Procedure to make a group of homozgous recessive individuals! you keep crossing one of the progeny to one of the parents and take away anything that is not homzogous recessive, keep inbreeding and crossing and crossing until you have pure homozgous recessive
gene linkage
Genes on different chromosomes are unlinked
Genes far apart on same chromosome are unlinked
Genes close together on the same chromosome are linked
Linked tend to be inherited together (do not follow independent assortment)
Linked genes can be separated by a recombination event (crossover)
gene linkage 2
ex. pair heterzgous for A and B and that parent makes gametes, if A and B totally independent of eachother and not linked then what we have been saying before all the different options here are equally likely so you would have 25% of the time the gamete would be AB, 25% ab, …. etc linkage means stays together more than percentage would indicate
parental chromosomes= exactly same combo of A and B,
recombinants= recombination occuring, recombination of alleles A and B found on parental chromosome are different, like aB combination is not found on any parental chromosome
so 50% recominbinant and 50% parental totally chance*
but linkage parentals are greater than 50%**** MEANS LINKAGE
Recombinance <50% MEANS LINKAGE
gene linkage example
this would tell us GENES DEFINTELY LINKED close to each other on chrosome, 10% recombination means the genes are 10 map units or 10 centimorgans apart
what allows recombinatin to occur, crossing over molecular scissors cross btw A and B to allow alleles to swap! closer they are to eachother hte less liekly it is the little scissors will hit right inbetwen them and the less likely you are to have recomibination** chance of them moving togehter way higher, chance of them having a tiny little cut bettween them is less likely can use recombination frequency to estimate how physically close two genes are to each other on chromosome
incomplete dominance
also called blending! when heterzgous also has its own phenotype; big example is the flowers, if you have red AA, pink Aa, white aa; for complete dominance Aa should be red also, but this is a case where heterzgote doesnt have dominant phenotype has a blended phenotype in this case pink is a color blend between red and white*
In incomplete dominance, phenotype of dominant heterozygote ≠ dominant homozygote
Instead, heterozygote has an intermediate phenotype
Example: 4’o clock plants. AA is red, Aa is pink, aa is white
Aa × Aa cross produces F1 with 25% red AA, 50% pink Aa, 25% white aa
Need both A alleles to provide full redness, one A allele is not enough
double crossovers/recombinants
Can have more than one crossover between genes
ABC/abc with one crossover gives Abc, aBC
ABC/abc with two crossovers can give AbC, aBc
When counting RF, double crossovers are counted twice
If double crossovers are only counted once, this will underestimate map distance
Example: if no marker between A and C, can’t distinguish WT and double crossovers
- when try to determine recombination fq know how many recombination events happened, double cross over means cross over and cross back source of error doesn’t look like anything has happened but you the key is it did and so it is an error
codominance
Codominance: no one allele is dominant
Each allele contributes to phenotype
Typically due to production of distinct proteins by different alleles of a gene
ABO blood groups = codominance, Ia Ib codominant, have blood type AB have and express A and B on surface of red blood cells and have it
A allele produces A surface antigen, B allele produces B surface antigen
O allele produces no surface antigen
AA or AO yields only A antigen
AB yields both A and B surface antigens
lethal alleles
Lethal alleles kill organism
Can be dominant or recessive
For a recessive lethal, aa is lethal, so only AA and Aa survive
Recessive lethal has an altered 1:2 genotype ratio, instead of 1:2:1
ex. monohybrid cross Aa and Aa, expect genotype ratio of 1:2:1, lethal allele gives you 1:2 so what we are saying here is that everythign with that genotype dies** examples in nature where something in nature homoxgous recessive phenotype is embryonic letahl an embyro with that genotype will not survive, do not see all boxes on a punnet square only see the other three not the homozgous recessive box* be aware of that as pattern if see homoz recessive indivdiuals totally missing, could be because maybe homozgous recessive genotype is embryonic lethal**
human chromosomal number
Humans have 46 total chromosomes (23 pairs)
22 pairs autosomes
1 pair sex chromosomes
Humans are normally diploid
Aneuploidy = aberration from normal diploid state
we should have 2 copies of each chromosome, 3 copies is=
3 copies of a chromosome = trisomy, 2n+1=47
1 copy of a chromosome = monosomy, 2n-1=45
We normally have 46 chromosome adn 23 pairs in somatic cells (not egg and sperm)
sex determination
In humans, sex is determined genetically by sex chromosomes
XX = female, XY = male
Presence of Y yields maleness
Random assortment of X and Y in gametes gives 50% daughters, 50% sons
x chromosomal inactivation
females have two copies of X chromosome, in any given cell only one Xs expressed other one is turned into really condensed heterochromatic form (condenses chromatin) refered to as barr body also called x inactivation** and it is random so in any one of your skin cells one of you X chromosomes will be randomly inactivated, in the next skin cell the other X may be randomly inactivated should be about 50/50 through our bodies but in every one of our cells only oen of our x chromosomes in inactive
explains why having extra X chromosome in aneuploid individual not serious, can make Barr body out of it; doses of X chromosomes is already unusual**** during replication and cell division x made into bar body (X inactivated chromosome) one of the last chromosomes to replicate takes a while to replicate bar body and take it apart**** has to be decondensed so just takes a second, can’t go into replication quite as easily as other chromosomes not in super crunched state
X chromosomal inactivation 2
Females are XX, but only one X is expressed
One X chromosome is turned OFF in each cell = Barr body
X inactivation is random and leads to mosaics in female (e.g., calico cat)
Explains why sex-chromosome aneuploidy is less severe than autosomal aneuploidy
During normal cell cycle in females, inactivated X chromosome is one of the last to replicate
Y chromosome
Males receive Y chromosome from father
Presence of Y chromosome determines maleness
Y chromosome is tiny and has very few genes
Kleinfelter’s and Turner’s
(talked about this also in reproduction chapter)
XXY = Kleinfelter’s male
XO = Turner’s female
Both Kleinfelter’s and Turner’s individuals are sterile
Both result from nondisjunction of sex chromosomes in meiosis
Instead of carrying X or Y only, sperm will carry XX, XY, or O (nothing)
Instead of carrying X, egg will carry XX or O
Can also get XYY males and XXX females via nondisjunction
x- linked recessive
Tends to affects only males, females are generally carriers
From carrier mother (XAXa), 50% of males affected
From affected mother (XaXa), 100% of males affected
Daughters may be affected if both mother and father have the allele
More males than females are affected! because in a male****
autosomal and x-linked inheritance
Autosomal genes have same inheritance pattern irrespective of sex
X-linked genes show distinct pattern of inheritance
Females get one X from their mother, one X from father
Males get their X from their mother
If males have an X-linked recessive mutation, they will be affected
Cytoplasmic inheritance of mitochondria
Sperm has little cytoplasm, contributes few to no mitochondria to zygote
Egg has large cytoplasm, contributes most or all mitochondria to zygote
All mitochondria and their DNA are maternally inherited
Where trait always inherited /passed from mother to child! think about mitochondrial dna there is this other thing totally different from nuclear dna, mitochondria DNA has a totally differnt pattern they throw in to shake that up!
get all mitonchondria dna from mother* NEVER passed from father to child ever, egg contributes all mitonchondira, sperm contributes no mitochondria** ALWAYS MOTHER TO CHILD*
penetrance
Incomplete penetrance: genotype may not always cause effect
100% penetrance = every individual will be affected
75% penetrance = 3/4 of people with genotype display mutant phenotype
just because have genotype doesn’t mean will always express phenotype with it, like cystic fibrosis or hemophilia genotype translates very strongly into phenotype, assuming genotype is 100% penetrance if you have genotype you will have disease
but it is also possible for a disease to be 75% penetrance, means even if have genotype only 75% chance you will have phenotype
Expressivity
Expressivity: affected phenotype varies in its severity
Expressivity can influence age of onset, or range of affected tissues
high expressivity- very high severity, very bad symptoms
versus low symptoms low severity of symptoms is low expressivity
leaky and null mutations
Null mutant = total loss of function (e.g., gene deletion or nonsense mutation)
Leaky mutant = partial loss of function (e.g., enzyme loses some activity)
Consider gene A that makes enzyme catalyzing 1 → 2
Null mutant in A will block reaction completely
Leaky mutation will reduce level of 2
Leakage can alter expressivity or penetrance
nature of mutations
Mutation = error in DNA sequence
DNA replication mistakes, spontaneous chemical changes in bases
Chemical and environmental mutagens (e.g., UV, X-rays)
Mutations can affect transcription (e.g., promoter or enhancer)
Mutations can affect splicing (e.g., change splicing pattern)
Mutations in coding sequences (e.g., silent, missense, nonsense, frameshift)
Mutation can alter protein function (e.g., Tyr → Ala change blocks phosphorylation)
Many mutations are detrimental, but some are helpful (evolution)
promoter mutations- deletion no transcription of gene! if gene codes for an enzyme and nezyme is made but protein is nonfunctional wrong 3 structure or cannot show same level of activity normal protein would, then something about the gene itself is mutated! missense, nonsense some mutaitons. 2. if they talk about exons and introns in protein then problem si with splicing 3. Clue protein works normally but too much of it or too little of it then think abotu regulatory sites somethign wrong with transcription factor, promoter or enhancer, TF supposed to bind to thsoe sites dial turned up too high or low on transcription but when make the protein it is normal but too much. 4. sort out mutation in an enhancer vs a promoter, for a certain gene there may be an enhancer that is very mportant to expressing the gene in brain and not hte stomach if have problem tissue specific when protein is made it is normal, but not made in brain but it is made in the stomache then that is an ehnacer tissue specific form of regulation. 5. if protein isn’t made at all problem with promoter bc need promoter to turn on transcription everywhere!
temporary mutations
Can make a mistake in transcription (i.e., DNA → RNA)
Can make a mistake in translation (i.e., RNA → protein)
These errors are less important due to rapid RNA, protein turnover
In contrast, DNA alteration is permanent and heritable
*errors way less important, cna get bad patch of protein but less worse than error in dna which would be bad dna made forever in that person*
sometimes they will ask about what kind of error is the most serioius= obviously anything heritable will be the worst kind to have**
translocations and inversions
Mutation can be simple base substitutions, additions, or deletions
But, can have larger-scale effects on the chromosome (larger scale chromsome mutaiton huge deal, or translocation piece of one chromosome breaks off and re-attaches to another)
Large deletions may remove one or more genes
Inversions flip the direction of a chromosomal segment
Translocations break and re-attach one chromosome piece to another
Translocations can fuse genes together, fuse promoters and enhancers to wrong genes
Translocations often activate proto-oncogenes
REALLY MESSES UP REGULATION* have chunk of dna moving away from the nearby regulatory elements supposed to govern its expression, coming under the control of a different promoter somehwere else so many famous examples of this ascociated with cancer, proto-oncogones which normally help with cell growht become activated in an unregulated way so become oncogene genes*
definition of an inversion
Inversions flip the direction of a chromosomal segment
translocations definition
Translocations break and re-attach one chromosome piece to another
Translocations can fuse genes together, fuse promoters and enhancers to wrong genes
Translocations often activate proto-oncogenes
mutagens and carcinogens
External chemicals can mutate DNA
Mutagen = chemical that causes mutations in DNA
Somatic mutation → mutation in body tissues
Germline mutation → mutation in gonad, passed to progeny
Somatic mutations are not heritable, but may result in cancer
All mutagens are carcinogens
Some mutagens are “activated” by liver enzymes
Ames test: bacterial test to assay mutagenicity of a given compound
Somatic mutation →
Somatic mutation → mutation in body tissues
Somatic mutations are not heritable, but may result in cancer
somatic cells are anything not repdouction, not germline= serpmatocytes, spermatids, spermatozoa, precursor stem cells that give rise lots of stem cells in testies get to primary spermatocyte goes to …… anything involved in pathway of cells; for females it would be stem cells in ovary then primary ooctye, secondary oocyte and the ovum*
this is important becuase if at beach get UV damage to skin cells, maybe even get skin cancer that isnt’ heritable something that happened to them in lfietime but if get zapped by xray tested or ovaries mutaiton in germline that gets passed on, so much bigger deal to have germlien mutaitons, some mutations in every cell of body part of someone’s genome** distnction is have a mutaiton that underlines cancer in someone’s body but mutaiton arose during their lifetime not something they inherited not heritable or passed onto patients family
Germline mutation →
Germline mutation → mutation in gonad, passed to progeny
Ames test
- bacterial test to assay mutagenicity of a given compound
- bacteria incubated with some novel compound that compnay X wants to put into its detergent, bacteria cells are incubated with the compound and then the assay will usually tell whether their ability to use nutrients changes or whether there is some kidn of fundamental mutaiton in nutrient needs of bacteria, easiest thing to test for so if this chemicla is causing mutation then resason to not approve it for consumer use
- newer version of ames test, ltos of variations in hwo this can work- researches do everything I just mentioned but then also incubate new compound with liver cells* let the liver cells interct with teh chemical, liver cells try to detoxify compounds and novel compound and after they do that that produces new metabolites and downstream products of metabolizing compound- after liver tries to process it one of the downstream by products could be mutagenic, ames test 101 and ames test next generation tests not only original compound btu also metabolites produced when original compound is processed by liver cells*
Mutagen = chemical that causes mutations in DNA; assumption of public health anything that changes someone’s dna puts at higher risk for cancer* so anything that is a mutagen that is a basis for regulating it as a probably carcinogen**
big deal because allwoed companies to figure out if the chemicals had bad side effects of raising ppl’s risk for cancer
Common inborn errors of metabolism
- Many human diseases result from recessive mutations in metabolic pathways
- All below are autosomal recessives except for Huntington’s which is autosomal dominant*
- Phenylketonuria (PKU)
- Sickle cell anemia
- Cystic fibrosis
- Tay-Sachs
- Huntington’s disease
- EVERYTHING HERE IS AUTOSOMAL RECESSIVE
Phenylketonuria (PKU)
Phe → Tyr is blocked, accumulation is toxic and can cause retardation
Can alleviate with phenylalanine-poor diet
So we use phenylalanine to make tyrosine and then what that pathway is blocked we have a buildup of phenolalaynine which is toxic to cells especially neurons, sometimes with toxic byproducts buildign up in cells bad for all cells but see the effects especially quickly with neurons in brain very sensitive cells, presenting symptom would be a set of cognitive issues*
People who have PKU can try to eat a special diet that doesn’t have a lot of Phe
Cystic fibrosis
Abnormal mucus secretion, major respiratory defects
Can clear some mucus from airways by chest percussion
Also autosomal recessive, people get really really thick muscus secretions and this effects different areas of the body that have ducts, but the presenting symptoms often have to do with respiratory passages being very clogged by mucus
Little kids who have this have to be patted on the back
Sickle cell anemia
Missense mutation Val6 → Glu6, causes hemoglobin crystallization
Sickle-cell shaped RBC blocks vessels, has shorter lifespan
Tay-Sachs
Lysosomal storage disease: can’t break down certain lipids, accumulation is toxic
Severe defects in nervous system, retardation
Huntington’s disease
Autosomal dominant neurodegenerative condition
Late onset in 30s or 40s, eventually fatal- important to how disease allele is perpetuatd in population, no carriers when it comes to something autosomal dominant, if disease that killed ppl when babies expect disease allele to die out*
Obviously carry it and give it to your children, if you have one disease allele you will get the disease, if killed when baby or child you would not be able to pass the allel on so from an evolution point of view the allele would die out, so the fact that it has a late onset could think about that as a strategy for the allele to continue in the population* if it wasn’t that way hungtington’s disease would not exist* In terms of how it comes up in questions, they want you to know huntington’s disease as a representiative example of AUTOSOMAL DOMINANT INHERTIANCE*** that pedigree could be for which of the following* will give you examples know this one is autosomal dominant*
polygenic/non-mendelian inheritance
In polygenic inheritance, many genes influence phenotype
Inheritance pattern is complex = non-mendelian
Interplay of many alleles → increased risk for a disease
Much more common scenario
epigentics
Changes to gene expression can be caused by mechanisms other than changes to DNA sequence
Changes are heritable
Methylation of DNA or histones tends to inhibit gene expression
Imprinting means gene expression is influenced by which parent (mother or father) a gene variant is inherited from
Imprinting occurs during formation of gametes
Sometimes how an allele acts in someone actually depends who gave them the allele, if get the allele from dad for specific diseases get the diseases, if get hte identical sequence but happen to get the allele from your mom you do not get the diseaes certain genetic minds are obseessed with this, why is the gene comign from dad such a big deal
gene was imprinted by dad and that is how it is expressed differently** has to deal with some markings made based on parent who get a certain allele from and that has an influence on how allele is expressed**
Some change but not to dna sequence itself, to chemical group modifying dna or histones, these changes are heritable if you have a lot of methyl groups if you have them in certain portion of genome in the mom to some extent that can be passed onto offspring
1st Mendelian law: segregation of alleles
In a diploid organism, alleles segregate in meiosis → haploid gametes
Aa diploid produces 50% A gametes, 50% a gametes
Can visualize with a Punnett square
AA × aa yields 100% Aa progeny in F1
Aa × Aa yields F2 with 25% AA, 50% Aa, 25% aa (1:2:1 ratio)
1:2:1 genotype ratio = 3:1 phenotype ratio
2nd Mendelian Law: Independent Assortment
Alleles of different genes assort independently of one another
AaBb diploid produces AB, Ab, aB, ab gametes in equal proportions
AaBb × AaBb dihybrid cross yields a 9:3:3:1 phenotype ratio in F1 (AB:Ab:aB:ab)
A 3:1 phenotype ratio is observed for A
A 3:1 phenotype ratio is observed for B
Each gene sorts as in a monohybrid cross, independently of the other gene
Law is true for genes that are unlinked
recombination frequency
Recombination takes place between homologous chromosomes during meiosis
Example: A and B are linked, father is AB/ab. Gametes are mostly AB and ab
But, crossover between A and B yields recombinant gametes: Ab and aB
Recombination frequency (RF) is proportional to gene distance
RF = # recombinant gametes/# total gametes
1 % RF = 1 cM distance
Can use RF to map genes with respect to one another on chromosome
A is 4 cM from B; A 10 cM from C; B is 6 cM from C. Order = ABC
Pedigrees
Males are square, females are circles
Filled in square or circle = affected
Half-filled circle or square = carrier (if genotype is known)
1. Autosomal recessive
2. Autosomal dominant
3. X-linked recessive
4. X-linked dominant
X-linked dominant
From affected father (XAY), 100% of daughters affected, 0% of sons affected
From heterozygous mother (XAXa), 50% of daughters and sons affected
From homozygous mother, (XAXA), 100% of daughters and sons affected
General Rules for Solving Pedigrees
Males and females are equally affected → autosomal
Sex bias in inheritance (often, significantly more affected males) → X-linked
Phenotype “skips” generations → recessive
Phenotype affects each generation → dominant
Use Punnett squares and back-test your assumptions
Autosomal dominant
Affects males and females equally
An affected individual must have an affected parent
Homozygous parent: 100% of progeny are affected
Heterozygous parent: 50% of progeny are affected
Autosomal recessive
- Affects males and females equally
- Unaffected carrier parents (Aa) can have affected children (aa)
- Phenotype can “skip” generations, due to unaffected carriers (Aa)
- Inbreeding will increase frequency of affected children
- Inbreeding means mating between genetically-related parents
- Outbreeding, by contrast, means mating between genetically-unrelated parents
Probability
Probability of two combined events (A and B) = p(A) × p(B)
Probability of having two boys = 1/2 × 1/2 = 1/4
Probability of having affected girl from recessive carrier parents = 1/2 × 1/4 = 1/8
leaky and null mutations 2
basically a mutation can cause total loss of function for a protein or partial loss of function so a null mutation is the complete turning off of function, you do not get a protein at all or protein totally nonfunctional
leaky mutaiton- what is leakign through is some function, not as bad means the enzzyme protein product would lose some of its function but not a 100% so some normalcy that leaks through in a leaky mutation*
so which is worse= null*
nature mutations 2
can come from chemical compounds in environment, preserviatives in meat, things that have the capacaity to alter DNA
important to talk about all hte ways mutations can have an affect:
- you can ahve a mutaiton in the coding portion of a gene, meaning get an actual different pattern of amino acids
- mutations affect regulation of gene, like in promoter makes gene more or less likely to be expressed
- mutation in enahncer further away, more improtant to see if gene expressed in certain moment in certain cell
- mutaitons that affect splicing
- mutations that make it harder to phosphorlate proteind own the line, v important for enzymes that get activated through phosphorlyation, tyrosine supposed to be phosphoflrated but no tyrosine there then cannot turn onenzyme because if some other amino acid there cannot phosphorlate** very common mcat question- describe a scenario gives you choices for what the nature of the mutation is, if activity of a protien is the same, then coding regions like exons are probably fine, if you have the activity of the protein is fine but you have 5x as much as you are exposed to or 1/5 as much then it is probably an issue with regulation* if have extra section to protein supposed to be intron but didn’t get spliced out that is a problem with splicity so be able to speculate about where the issue is where the mutation is falling in the genome**
tip mcat
sometimes give you super super precise mutaiton in splice site donor, splice site acceptor, mutation in enhancer upstream of the gene…. and it is importnt to remember for those questions there is a problem with splicing something going on with splicing but I do not have enough information to knw what the issue is with splicing, but just pick any scenario they give you thta involvces splicing** could it be this, or if think problem has something to do with regulation* gives you scenario problem with promoter then yes pick that even if more specific then could have gotten to with information provided**
hyperspecific answer- is this plausible do i have anything that contradicts this? if so that is the answer you chose
some sponagenous mutaitons
can be good and great for natural selection!
tay sachs 2
Lysosome’s job is to be garbage disposal for cell break things down using acid hydrolayses so if one of those enzymes is missing or mutated and lysozomes cannot break down a certain macromolecule then that macromolecule accumulates! a few different diseases that are an issue with breaking down lipids, so certain lipids accumulate and are toxic to cell, another situation like PKU when something is building up in cells, type of cells most effected is neuron, same thing said about PKU
kids do not live very long
When lipids accumulate in neurons, what is accumulating in general neurons are senstitive cells, so symptoms are cognitive decline and deficiets in nervous system
Imprinting
= means a gene that is passed down so say you inherit a certaing gene from your mom or certain allele then you express that gene, but it is possible in certain cases if you inherited the exact same allele from your dad you would not express it
So imprinting refers to some marking on allele depends if get it from mom or dad, doesn’t matter if get it from mother or father; genetic diseases two ppl with same exact genotype one will have the disease and oen will not, one inherited disease allele from dad one from mom and that makes differetnce in terms of impriting if disease allele is expressed or not; some marking that relates to parents and where alleles came from
consanguienous
means inbreeding
what penentrance means….. ex
whether genes are penetrant does not have to do with their physical location on the chromosome** also not something you look at for genes in relationship to eachother just say this gene is incompletely penetrant… etc just pertains to a single gene really
For probability punnet squares
OR means ADD; if question said probablity of having an affected daughter and ADD it to probability of affected son**
AND means multiply, probability of having an affected daughter AND having an affected son, so when two events and link them in a situation with word AND means multiply**
Q28. two parents are carriers for an autosomal recessive mutation that is 50% penetrant. What is hte probability that their child is healthy?
7/8
great example of an OR statement, can have a healthy child becuase AA or Aa or healthy child because kid has disease genotype but not showingup becuase of penetrant issue, two ways to be healthy and you add them
Gene linkage 4
parentals= means combinations they have in A and B is the exact same as the ones at the top
the other two are the recomibants they have a different A and B arrangement*
so we said parentals are 50% and recombinants are 50% of all the gametes* that would be A and B assort independently*, are NOT LINKED* or other way we can say this is they have a recombination frequency of 50% but that means that they are far apart* on the same chromosome or are on different chromosomes*
recombinaton 3 explained
If do nto get the EbW or eBw then you get recombinatin not found on same chromosome in parent but in mitoic process they are found oggether so they are recombinatnt***
Linkage looks atfrequency of E and B will combined, so what is hte frequency of them switching, what is the % that this happens?!
centimorogans= unit describes lieklihood of things crossing over together versus separetly, what is the likelihood these things will recombine
srves as an indicator at how likel these will swtich over, vs original alleles staying where they are, say 93 to 7% recombination event those are the things happen 7% of time- serves as an indicator of how likely these pieces are to stich over without both moving together, get percent value to tell you the genetic distance or gene map distance
7% means 7% of time they will not be inherited together they will be recombined
greater comibination frequency correspond with greater distance along chromosome,ti will never ever be greater than 50% for recomination, if genes are on completely separate chromosomes hten their recombinationf requnecy will be 50% just as much a chance of being inherited tgoether or combining and inherited separately with new combination of things
with alleles on new chromosome can come up with new concept known as linkage way of looking at likelighood two alleles will be inherited together*
linkage explained
with alleles on same chromosome can come up with new concept known as linkage way of looking at likelighood two alleles will be inherited together*
only look at if have alleles on same chromosome, say for ex the distance here is 7 cM and (centimorgans) and distance btw E and W is 35 cM tells us E and W are a lot further apart on chromosome than E and b and hte likelihood of them crossing over separately and beign recombied is inversely proportional to distance, E and b likely linked if odds of recombining are very very rlow like 7%
if odds of E and w recombine into something and eW recombine are 35%, much bigger distance and greater chance of them, much further apart on chromosome than E and B inversely proportional to distnace, highly linked if odds of recombining are very low
Linkage clearly defined cont.
less than 50% so yes on same chromosome but further along chromosome far greater distance of E and Ws recombining at that frequency basic rule is the more closely linked these alleles are they will be clsoer on the chromosome and less likely to recombine in process of meosis, only relevant for things on same chromosome, otherwise 50% hance due to chromosomes will allign differntl on metaphase plate and no desire of them to be on oen side or the other.
so closer they are more closely linked they are closer on chromosome and less liekly to recombine, only relevant for things on same chromosome
linkage=likelihood two alleles will be inherited together
