Genetics

Question 1

wild type vs mutant

Answer 1

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

Question 2

genotype and phenotype

Answer 2

Genotype = genetic makeup of an organism

Phenotype = the appearance of an organism

Can have same phenotype but a different genotype**

Question 3

homozygotes and heterzygotes

Answer 3

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

Question 4

what is locus

Answer 4

IT IS A LOCATION**

Question 5

monohybrid cross

Answer 5

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

Question 6

dihybrid cross

Answer 6

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

Question 7

generation nomenclature

Answer 7

P = parental generation

F1 = first filial generation

F2 = second filial generation (progeny of F1 intercross)

Question 8

dominant and recessive alleles

Answer 8

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)

Question 9

genes, alleles and loci

Answer 9

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

Question 10

dihybrid cross cont. 2

Answer 10

9:3:3:1

these represent ratio of phenotypes for a dihybrid cross!

Question 11

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)

Answer 11

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

Question 12

testcross

Answer 12

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!!!

Question 13

backcross

Answer 13

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

Question 14

gene linkage

Answer 14

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)

Question 15

gene linkage 2

Answer 15

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

Question 16

gene linkage example

Answer 16

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

Question 17

incomplete dominance

Answer 17

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

Question 18

double crossovers/recombinants

Answer 18

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

Question 19

codominance

Answer 19

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

Question 20

lethal alleles

Answer 20

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**

Question 21

human chromosomal number

Answer 21

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)

Question 22

sex determination

Answer 22

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

Question 23

x chromosomal inactivation

Answer 23

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

Question 24

X chromosomal inactivation 2

Answer 24

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

Question 25

Y chromosome

Answer 25

Males receive Y chromosome from father

Presence of Y chromosome determines maleness

Y chromosome is tiny and has very few genes

Question 26

Kleinfelter’s and Turner’s

(talked about this also in reproduction chapter)

Answer 26

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

Question 27

x- linked recessive

Answer 27

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****

Question 28

autosomal and x-linked inheritance

Answer 28

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

Question 29

Cytoplasmic inheritance of mitochondria

Answer 29

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*

Question 30

penetrance

Answer 30

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

Question 31

Expressivity

Answer 31

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

Question 32

leaky and null mutations

Answer 32

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

Question 33

nature of mutations

Answer 33

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!

Question 34

temporary mutations

Answer 34

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**

Question 35

translocations and inversions

Answer 35

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*

Question 36

definition of an inversion

Answer 36

Inversions flip the direction of a chromosomal segment

Question 37

translocations definition

Answer 37

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

Question 38

mutagens and carcinogens

Answer 38

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

Question 39

Somatic mutation →

Answer 39

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

Question 40

Germline mutation →

Answer 40

Germline mutation → mutation in gonad, passed to progeny

Question 41

Ames test

Answer 41

• 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

Question 42

Common inborn errors of metabolism

Answer 42

• 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

Question 43

Phenylketonuria (PKU)

Answer 43

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

Question 44

Cystic fibrosis

Answer 44

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

Question 45

Sickle cell anemia

Answer 45

Missense mutation Val6 → Glu6, causes hemoglobin crystallization

Sickle-cell shaped RBC blocks vessels, has shorter lifespan

Question 46

Tay-Sachs

Answer 46

Lysosomal storage disease: can’t break down certain lipids, accumulation is toxic

Severe defects in nervous system, retardation

Question 47

Huntington’s disease

Answer 47

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*

Question 48

polygenic/non-mendelian inheritance

Answer 48

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

Question 49

epigentics

Answer 49

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

Question 50

1st Mendelian law: segregation of alleles

Answer 50

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

Question 51

2nd Mendelian Law: Independent Assortment

Answer 51

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

Question 52

recombination frequency

Answer 52

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

Question 53

Pedigrees

Answer 53

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

Question 54

X-linked dominant

Answer 54

From affected father (X_AY), 100% of daughters affected, 0% of sons affected

From heterozygous mother (X_AX_a), 50% of daughters and sons affected

From homozygous mother, (X_AX_A), 100% of daughters and sons affected

Question 55

General Rules for Solving Pedigrees

Answer 55

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

Question 56

Autosomal dominant

Answer 56

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

Question 57

Autosomal recessive

Answer 57

• 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

Question 58

Probability

Answer 58

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

Question 59

leaky and null mutations 2

Answer 59

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*

Question 60

nature mutations 2

Answer 60

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**

Question 61

tip mcat

Answer 61

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

Question 62

some sponagenous mutaitons

Answer 62

can be good and great for natural selection!

Question 63

tay sachs 2

Answer 63

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

Question 64

Imprinting

Answer 64

= 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

Question 65

consanguienous

Answer 65

means inbreeding

Question 66

what penentrance means….. ex

Answer 66

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

Question 67

For probability punnet squares

Answer 67

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**

Question 68

Q28. two parents are carriers for an autosomal recessive mutation that is 50% penetrant. What is hte probability that their child is healthy?

Answer 68

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

Question 69

Gene linkage 4

Answer 69

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*

Question 70

recombinaton 3 explained

Answer 70

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*

Question 71

linkage explained

Answer 71

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

Question 72

Linkage clearly defined cont.

Answer 72

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