3.2-3.3, 4.2-4.4, 15.1 Flashcards

Question

spermatogeneiss in humans produces four spemr from each priamry spermatocyte

Answer 1

production of sperm or spermatogensis begins in testes in germ cells known as spermatogonia mitotic divison of spermatogonia produce many diploid cells, the primary spermatocytes unline primar oocytes, primary spermatocytyes undergo a symterical meisis 1 producing two secondary spermatocyes each of which undergo a symetrical meisiss 2 at the conclusionof meisis each orginal primary spermatocyte thus yeilds foru equivlent haploid spermatids these spermatides mature by developing a charcetric whipliek tail and by ocncnetratng their chromsla materialin a head thereby becoming functional sperm a human sperm much smaller than the ovum it will fetrlize, contains 22 autsomes and either an X or Y chromsome the timing if spemr production differs radically from that of an egg formation the meitic divisons that convert primary spermatotctes to spermatids begin only at puberty but emsis then continues throughhout a males life the entire process of spermatogenis takes abt 48-60 days: 16-20 for meisis 1 the same for meisis 2 and 16-20 for the maturatrion of spermatids inyo fully functional sperm within each tesis after puberty, millions of sperm are always in prodcution and a single ejaculate can contain up to 300 million over a lifetime a human male can rpoduce hunders of billions of sperm almost equally divided between those bearing an x and those y chromose

Answer 2

Sutton first psited the idea that genes are contained on chromsomes- chromsome tehroy of inehrtiance Sutton disocvered tha the behaviour of chomsomes during emsisi correlates with and can explain emdnels alws of inehrtance the events of mitsisi and meisis and gemotgensis ensure a constant number of chromsomes in teh somatic cells of memebrnes of species over time as you woudl expect for genetic amteria Nettie Stevens showed that sexual morpholgy is associated with the inehrtance of partcualr chromsomes, the sex chrosmomes stevens results were the first to demontrate that a trait (sex) is correlated with the inhertance of a partcular type of chromsome from a sperm- the S or Y many sicetntsist werent willing to accept the chorsome tehroy as fact they argued that sex might be a unique trait fundamentally diff than otehr phenotypes geneticsts at the time wanted to etst whetehr the trastnsmission of charcertci other than sex could be corelated with teh trasnmisison of a specific chrosmome that could be ID's in the micriscope

Answer 3

Morgan headed the research group whose finding s established a firm base for chromsome tehory morgan chose to work with Drosophila bc its short gen time and high preoridyction in 1910 a hwite eye maled appeared - mutation apprently altered a gene detrmining eye colour changing it from wild type allele red to new allele white when white eyed male crosses with red females all flies of f1 were red - red dom to white establishing a pattern of nomecualtrue for drophila genetics - normal wild type of white gene is w+ for red and mutant is w (lowercase shows receissve to wild type w+)

Answer 4

morgan tehn crosses the red eyes males of f1 gen with their red eyes sisters and obtained an f2 gen with 3:1 ratio of red to white among the red two females were present for every one male and all white were male resulst are diff than equal tarmssion to both sexes of mendialin traits the fruit flies ratio was unequal in genders by mating f2 red female white whoet brothers, tehre were some whit efemales white female with red male gave all red eey duaghetrs and white eyes sons crisscross inehrtance bc males inerti coloru from tehir mothers while the daughters inherit their eye colour from their fathers from the data, morgan rewaosned tah the white gene for eye coloru is x linked - carried by x chromsome the Y chromsome carries no alelel of this gene for eye colour mles only have one copy of the gene which tehy get from mom along with the x chrosmome - the y coems from dad males are hemizygous for eye colour genes bc diplodi cells have half number fo alleles carried by females on tehri two x chromsomes if the single whit egene on X chrosmome of male is wild type w_ - he has red eye but a hemizygous male would have white eyes w females with two x can be three types of genetypes c chromeoms in sons of white eyes mother (ww) must carry w allele so sons are white but bc duaghters of red eye fatehr (w+Y) msyt receive w_ bearing x chromsome from dad so they haev red eyes

Answer 5

although morgans work stringly supported the hyoetsjsi that teh white gene lies on the x chromsome, he himself continue dto quetsion the valdity of the chrosome tehroy until Bridges found evdience Bridges repeated experment between white eyed females and red eyes male but this time on larger scale - progeny was mostly red eye female and whit eey emale but tehre was 1 in 200 of red eye male and white eye female bridges hypoethsized tah these exceptions arose throughr are events in whci the x chrosmome fails to seprate during emisis in females he called the failure in chrosmome segregaton nondisjunction mistakes leading to nondijsution would result in some eggs with two x and otehrs with non so there could be zygotes of : XXY, XXX, XO (x from dad) and OY (y from dad) when bridges examined teh sex chrosmome of rare white eye female produced in teh cross he fond that tehy were XXY indivduals who receiced X with ww alelel from motehrs and exceptuonal red eye male from XO - tehy got their x from their dad showed behaviour of x chromsome during mistakes indicating that x chrosme carrie gene of eye collour suggest zygotes with two other avnroal sex chromome akrytotes expected from nondisunction (XXX and OY) die in development bc XXY white females have trhee sex chrosmomes, bridges reasoned they would rpoduce 4 kinds of eggs: XY, X or XX and Y bridges imagined that during emisis 1 eiehr the two x chromoems pair leaving y on its own or x and y pair leavin x on its own in first scenarion, one x migrates to each pole and y migrates to one or the otehrs reuslting in XY oand X gametes in second scenari the x and Y migrate to opp sides and X goes to either pole giving XX and Y or XY and X gametes bridges next predicted that fetrlizatin of tehse foru kinds of eges from XXY female by normal sperm would genrrate an array of sex chrosmome karyotes associated with specific eye colorus in rpjgeny bridges verified all rpeidction when aanlzing the colours and sex chrosmomes he showed cytologically that all white eye female emegring from cross has two x and one y whike one half of whit eeye males has a single x and two Y bridges paisntaking osbervatin provided evdience tah sepcif genes do reside on specifi chromsomes

Answer 6

mendel had assumed that geens are located in cells the chrosmome theory assignemed the genes to specific kind of strcuture within cells and explained alternative allels as phsycially matching parts of homolgous chromsomes theroy provided an eplantion of mendels laws the mechnaism of meisis ensures tha the two chromsomes in a homolhosu pair segrgate to diff gametes (unless nondisjunction) acocuntng for teh segrgatuon of alleles predicted by mendels first law bc each homolgosu chromes pair aligns idnepdnetly of all otehr at mesisi 1, genes carired on diff cormoesm assort indepdently as predicted by emdnels second law the chrosmome tehroy is also able to epxlan the creation of new alleles through muattion, a spontanosu change in partucalr gene if mutatin occurs in germ line, it can be trasmitted to subsqeunet generations finlaly through mitic cell divisons in teh embryo and after birth each cell in a multicellualr organism receives the same chromsomes and thus the same maternal and patenral alleles of each gene as teh zygote reied from the egg and spemr at fetrliztaon in this way the chrosmems and genes making up an idnivsuals genome remain constan throughout life

Answer 7

red green coloir blindness is a receive condition that runs in fmailies and affect mostly males Wilson combined family studies of inehrtance of colour blidnness withr ecent knwoeldge of rles of X and Y chrosmomes in sex determination to make the first assignment of a human gene to a partciualr chrosome the geen for red green colourblindness he said lies ofn X chrosmome bc conditon is usually passed from maternal grandfather through an unaffeccted carrier mother to half grandosns Wilson reseaosned that males have only one copy, they are hemizygous, for all x linked genes bc males only need one recessive allele from their mother to be afefcted it makes sense that codnitions caused by receisve x linked allele would be mroe fequement in males such conditions, like colour blindess, usually skip a generatuon bc an affected male would pass an x linked colour blindness alelel only to his duaghetrs who would be unaffected but could pass the colour blidnness allele to tehri sons several years after wildosn made geen assignemnt, pedigree analsys established that avrious forms of hemophilia reuslt from muattions on x chromsome that giev rise to rare recessive trait

Answer 8

x linked reccsive: - appears more in males than females bc female needs two copies whereas hemizygosu amle with only one copy has the trait - muatnt alelle never passes from fatehr to son - an afefcetd male passes muatton to all daughters whcih are carriers and agrandons have half chance - trait often skisp a gen - trait appear in sucesive gens when sister of an afeftced male is a carrier - w/ rare affected female all sons are affect ed and all duaghetrs are carriers x linked dom: - more females than male show - trait seen in most gen - all duaghetr but no sone of affected male has - sons and duaghetr of affected male have half chance of being affected - for incompete domiant x linked, carrier female may show trait in less extreem form y lnked: only in males all male decsnde of male have it females cant transmit or show in rare cases mustations on x are dom to the wild - then more females have it - ex. vitamin d resistant rickets

Answer 9

xx and xy present probelm taht requires dosage compensation x chromse has many genes and proetisn they speccy need to be present in same amounts in meale and female cells to compensaet for females having two x, one is inactavted most egenes on the inacted x are turned off x inactavtin hapepns two weeks after fetrlization each cell chosses one x chrosmome at random to condense into barr body and inactiavte it (dark chromsomes) x chrosmome inactivation is also kwnon as lyonization each embrynic cell decides indepdntly which x chrosome is inacted - the maternal or patenral gievn then the decisin is clnally perpetatted so all million cells decended by mitsisi from partcualr embrynoic cell condese the same x chromsome into barr body human females are aptchwork of cells conating a materanlly derived x active chrosme and other active patenral x the phneoemmn of x chosme inactiavtion may have inetresting effects on the traits controlled by x-linked genes when females are heetroyzgous at an x-linked gene, some parts of tehri bodies are in efefct hemizygous for one allele and the otehr are hemizygous for otehr allee in terms of gene function moreoevr hwich body parts are funatioanlly hemizgous for one allele or otehr is random (even in diendctal twisn its random) females hetrozygous for x-linked recieve of dysplasia have patches of skin taht lack swat glands interspred with nromal skin; depnd on which x hcromosme is inactieved each patch is a clone of skin cells derievd from a single embrynoic cell that amde teh decison to inactivate one of teh x chrosmomes anotehr ex. female hertozygous for x linke recesisve hemophilia may have symptoms of ehmophilia even if only carriers of alelle sevritu depdns on the random pattenr of inactvation of disease and normal cell the two tips of x chrosmome have pseudoauatosmal regions (PARs) contain geens also present at the tips of the Y chromsome to equalize the dosages of these genes in XX and XY cells, the APr genes on the BArr body X chromsome escape inactivation this featur eof doage comepsnation may explain why XXY males (klinfelter) and XO females (turner) have atypical mropholhical features x chrosme inactivatiin is common among mammals some organsims compensate for sex chrosmome difference in diff ways fruit flies hyperactiavte the single x chromse in XY male cells so that most X chrome genes produce twice as much proetin product as each x chrosme in female elegans ratchets down teh elevl of gene atcivty on each x in XX hermpahridets relatijve to single x in XO males

Answer 10

charcetrcis due to mauatton in SMY of Y chromosome (y linked) should also be dienficbale by pedigree trait would pass from fatehr to all sosn and to all furture male descents female wouldnt exhibit or transmit this hwoever besides dtermination of malesness and contirbutions to spemr formation and male viability, no clar cut y linked visible trait have turned up MSY region of y chrome contains few genes

Answer 11

not all genes that produce sexual dimophism reside on X or Y chromsomes some autsomal genes detrmine traits taht apepar in one sex not the otehr or with differnet extents sex limuted traits affect strcutrue or process found in one sex not the other muatton in geens for sex limted tarits inlfuence phontype of only sex with those strcyrues or processes ex. stuck is drosophilia males (female dont have strctrue so no imapct on them) sex-infleucned traits show up in both sexes but teh charcter ofssuch tarts may differ bc of hromaonal differences patenr baldness usually seen in males but hertozygous female dont show any hair loss homozygotes in both become bald but its late onset in females so its dom in males and reciesve in females

Answer 12

all chromomes in haploid gametes of diploid organism differ from one another - non homologous indivduals whose chrosmome number isnt exact multiple of haploid number for the species are aneuploids monosomic (2n-1) and trisimic (2n+1) most aneuplodyy create a gentic imabalnce taht is deletrous to the orgnism

Answer 13

in humans, monosmy for any autosome is geenrally lethal but medical egenticsts have reported a few cases of monomsy for chormsome 21 (smallest one) although with abnromalties the monosmic indivduals survievd for a short time beyond birth - simsilar with trsisomies idnivduals with trsimy for large chrosmomes immedly abrot in pregancy and trismy 19. 13 can survive a few months most freq observed human autsomal trismy is trsismy 21 as shortes human autsome, chromsome 21 conatin sonly abt 1.5% of the DNA in the human genome roughly 75% of trismy 21 do resul in miscarrage, some die in first year bc of heart defect or infection althrough consideable phenotypic vairation exists among ppl born with down syndrome, triats like intelcuatl disability and skeltanl abronamtlies are associated some ppl withdown syndrome have three copies of only one part rather than whole chrosmome extra copy of part if inherted through a robertsonian translocation

Answer 14

although the x chromsome is one of the longest human chrosmomes and contain 5% of dna in the genome, those with x aneuplody (XXY, XO and XXX) surive well explanation is the x chromsome inactivation equalizes expression of most x linked genes x chromsome inactviationsilences expression of most geens on one of two x chromsomes; the genes that escape x inactiavtion are mainly in the pseudoaudtomal regions of the x and y in the x aneuploids, all but one x is inactavted so the protein generated by x linked gene in auenplodi is same as typcial sexes human x chromsome anueplodies arent without consequence - xxy have klinelfter while xo have truner aneuploid have inferlity and skeletabl abnormalties - xxy male talla nd xo female short morpholhical abnromamlities are due to at leats abornal dosage in somatic cells of the 30 par genes = XO females have one copy fewer of each of these genes than typical female while xxy males have one copy more than males do one par egne shox (short stature homebox) encodes a proetin imprtant for bone dvelopment and is likely to play a leding role in the short stature of females with turner syndrome and the tallness of males with klinefleter interfilty of ndivual with the sydromes is likely for diff reason: abronal dosage in germ line cells of x-linke dgenes outside the pars germ line cells udnergo reverse x inactiaon - x chrosoome REactivation in females, x reactiavtion occurs in oogonia, germ line that divide mitotcally and whose duaghters devlop into oocytes that ndergo meisisi reactviation of inactvated x in oogonia ensure that every mature ovum receives an active x - if it dindt occur, half of females eggs would contain inactive x and would be incapable of suprpiting dvelopment afetr fertlization with x reactivation, oogonia in xx females have two fnctional doses of x chrosmome genes but corresponding cells XO females with turner syndrom have only one dose of the same genes and may undergo defective oogensiss in XXY males, x reactvtaon in spermatogonia, germ line that divide mitically and dvelop into spemratocytes that udnegro emisis to produce sperm, results in twice normal dose of x linked genes so they usually make no sperm

Answer 15

mistakes in chrosome segrgation during meisisi produces anueplodi of diff types if homolgosu chrosme sodnt seprate in meisisi 1 the two of teh resulting gametes will carry both homolhos adn two will cary neither uninion of the anueplodi gametes with nroaml one would produce aneploid zygote: half trsimic and half monosmic by contast if meiotic nondisjuction occurs during meisis 2 olnly two of the four resulting gametes are aneuploid aneuploid gamets produced by eitehr kind of mistake are also called unbalanced gametes bc not all teh geens are present in their nromal doses abrnoaml n+1 gametes resulting from nondisjunction in a cell that is hertozygous for alelles of genes close to the centroemre on the nondisjoining chromsome will be heteroyzgous if teh nondisjunction happens in the first meistic division but are homozygous if nondisjunction takes place in the second meistic disivison u can use this distnction to detrmine when and in which parent a aprtcualr nondisjunctin occured the nondisjnction veents that giev rise to down syndrome usually happen in mothers and during first emitic divison (if in fatehr then sually in second) molecualr studies have shown that many meitic nondisjunction events in humans result from probelms in meitic by tracking dna markers you can estalbish whetehr recomb took place along chrosme 21 dring meusisi that created n+1 gametes in many cases no recomb happened between homologous chromsomes - makes sense bc crossovers would hold maternal and paternal toegtehr in bivalent - ina sbence of recomb no mehcnsim exists to esnure that the chrosmes will go to opp poles at anaaphase 1 meitic recomb decereases in womans age

Answer 16

mistakes in chrosome segrgation in early mitotic division of zygote result in issues in mitotic nondisjunction failure of two sister chromatdis to ssperate during mitotic anaphase generates reciprocal trisomic and monosmic duaghter cells other types of mistakes like lagging chromatid not pulled to eiethr spndle pole at mitotic anaphase reuslt in a chrosmome loss that produces one monosmic and one diploid dughter cell in mutlciellaulr rogansi, aneuplodu cells from mitotic nonjdisnction or chroosme loss may survive and undergo furtehr rounds of cell divison producing clones of cells with abnormal chrosmome count nondisjunction or chrosome loss ocuring in ealry develop generate larger aneuplodi clones existence of aneuplodi and nromal tissues results in mosaic organism whose pheontype depnds on what tissue bears anueploid, number of anueplod cells and speific alleles on the genes on anueploid many exmaples of msocisicm involve sex chrosomes if an XX drophilia zygote loses one x during mititic divisin, result is a gynandormph composed of equal male ad female tissues many huamn females with tunrder ysdrome are mosiacs carryin some xx and some xo these induvdlas begin dveelopment as xx zygotes but with loss of x during early mitic divisons tehy aquire clones of xo cells simialr mosaicism involing autsomes also happens tehres midl down syndrome ariisng from mosicism of trismy 21 -soem nromal tissue amelriaets condition with the indivduals pheontype dpending on the partucalr distrbin of diploid vs anueplodi cells