Txhua tus paub tias nrog kev sib deev, ib yam kabmob tshiab tshwm sim los ntawm kev sib xyaw ntawm ob gametes (sex cells). Gametogenesis, los yog tsim cov hlwb tsim, tshwm sim los ntawm ib qho kev faib hu ua meiosis. Dab tsi yog qhov tseem ceeb ntawm cov txheej txheem no, dab tsi yog nws theem, peb yuav qhia hauv kab lus no.
me ntsis kev paub
Rau feem ntau cov kab mob sib txawv ntawm peb lub ntiaj teb, kev sib deev yog yam ntxwv. Hauv qhov no, gametes muaj ib nrab chromosome teeb, uas yog hu ua haploid (n). Raws li qhov tshwm sim ntawm kev sib xyaw ntawm gametes, lub zygote yog tsim, nyob rau hauv uas diploidy yog rov qab los, thiab cov txheej txheem ntawm chromosomes raug xaiv 2n, uas yog cov ntsiab lus ntawm meiosis (luv luv).
Piv txwv li, Drosophila (fruit fly) tsuas muaj 4 chromosomes - qhov no yog diploid teeb. Gametes hauv nws cov nucleus tsuas muaj 2 chromosomes xwb. Hauv tib neeg, hauv txhua lub cell hauv lub nucleus muaj 46 chromosomes, thiab hauv gametes (qe thiab phev) - 23 txhua.
Tab sisKev kho dua ntawm diploidy thaum lub sij hawm kev sib deev yog ib feem me me ntawm qhov tseem ceeb ntawm meiosis.
Chromosomes thiab chromatids
Yuav kom nkag siab cov ntaub ntawv hauv qab no, nws yog ib qho tseem ceeb kom nkag siab qhov sib txawv ntawm ob.
Chromosomes (tus qauv n yog siv) yog hu ua cov khoom siv caj ces, tab sis tsuas yog cov no yog DNA molecules (deoxyribonucleic acid), muab spiralized thiab nyob rau hauv lub nucleus ntawm hlwb ntawm eukaryotic (muaj ib tug nucleus nrog ib daim nyias nyias.) cov kab mob. Nyob rau hauv daim ntawv uas peb tau siv los pom lawv nyob rau hauv cov phau ntawv thiab cov ntaub ntawv siv (daim duab saum toj no qhia tib neeg chromosomes), lawv ua pom tau tsuas yog thaum lub sij hawm interphase, ua ntej cell division, thaum lawv twb ob npaug.
Tab sis cov chromatids (suav nrog) - qhov no tsuas yog cov qauv ntawm cov chromosome, uas twb dhau los ntawm cov txheej txheem ntawm kev rov ua dua (ob npaug) hauv qhov cuam tshuam ua ntej ntawm tes faib. Ib chromatid yog ib qho ntawm ob daim ntawv theej ntawm DNA uas txuas nrog lub sijhawm no los ntawm qhov tshwj xeeb constriction (centromere).
Tsuav yog ob lub chromatids txuas nrog lub centromere, lawv hu ua tus muam chromatids. Thiab tsuas yog thaum lub sij hawm kev sib deev ntawm cov hlwb (meiosis) lawv cais thiab sawv cev ntawm cov khoom ywj pheej ntawm cov khoom siv, thiab yog tias hla tau tshwm sim ntawm lawv (ntxiv rau tom qab), ces lawv tau hloov pauv hauv cov noob kab ke.
Txhua tus chromosomes sib txawv hauv cov duab thiab qhov loj hauv ib khub (zoo tib yam) khub. Tag nrho cov txheej txheem ntawm chromosomes hauv cov hlwb ntawm tib hom yog hu ua karyotype. Yog li, hauv tib neeg, karyotype yog 46 chromosomes,ntawm 22 khub yog homologous lossis autosomes, thiab 23 khub yog poj niam txiv neej chromosomes (X thiab Y). Hauv tib neeg gametes (phev thiab qe) muaj ib nrab (haploid) teeb ntawm chromosomes - 23 autosomes thiab 1 chromosome txiv neej (X lossis Y).
Tsuas meiosis muab cov txheej txheem hauv gametes.
Special cell division
Kev faib tshwj xeeb nrog kev tsim cov kab mob - meiosis (los ntawm Greek lo lus Μείωσις, uas txhais tau tias txo qis) yog ib txheej ntawm ob qhov sib txuas ntawm tes, vim tias cov nucleus faib ob zaug, thiab cov chromosomes tsuas yog ib zaug xwb.. Vim qhov no, muaj qhov txo qis (txo) ntawm cov chromosome teeb tsa hauv gametes los ntawm ib nrab, uas, thaum lawv sib koom ua ke, rov ua dua lub diploidy ntawm zygote. Qhov no yog nws qhov tseem ceeb lom zem.
Meiosis (nws theem) hauv txhua yam kab mob muaj sia tshwm sim tib yam:
- Thawj qhov kev faib (txo), tom qab ntawd tus lej ntawm chromosomes yog halved.
- Kev faib thib ob (equational) tshwm sim raws li kev faib yooj yim (mitosis). Nws tseem hu ua leveling.
thawj meiotic division
Thaum lub sijhawm npaj cov cell rau kev faib (interphase) hauv lub nucleus, tus lej ntawm chromosomes ob npaug (muaj 4 n), uas yog ib qho zoo rau cov hlwb uas faib los ntawm kev faib yooj yim (mitosis). Nyob rau hauv lub hlwb ntawm lub precursors ntawm gametes (nyob rau hauv tib neeg, spermatocytes thiab oocytes), xws li ob zaug tsis tshwm sim nyob rau hauv lub interphase, thiab lub cell pib meiosis nrog ib tug txheej ntawm 2n chromosomes thiab hla.cov kauj ruam hauv qab no:
- Prophase I. Nyob rau theem no, cov chromosomes ua denser thiab nyob ze ua ke. Conjugation (adhesion) ntawm homologous chromosomes (ib khub) tshwm sim, thaum hla dhau tshwm sim. Cov txheej txheem no yog tus yam ntxwv nkaus xwb rau meiosis (dab tsi yog lub ntsiab lus, peb yuav piav qhia hauv qab no). Tom qab ntawd cov chromosomes raug sib cais, lub plhaub ntawm lub cell nucleus raug rhuav tshem, thiab kev faib spindle pib tsim.
- Metaphase I. Cov spindle fibers txuas mus rau centromeres ntawm chromosomes, thiab lawv tus kheej nyob rau hauv lub division equator opposite ib leeg, thiab tsis nyob rau tib kab (raws li nyob rau hauv mitosis).
- Anaphase I. Spindle threads ncab cov chromosomes rau cov ncej. Luv luv, lub ntsiab lus thiab qhov tseem ceeb ntawm meiosis nyob rau theem ntawm kev faib - cov ncej muaj n chromosomes.
- Telophase I. Nyob rau theem no, lub hnab ntawv nuclear raug tsim. Hauv cov tsiaj txhu thiab qee cov nroj tsuag, kev faib tawm ntxiv ntawm cytoplasm tshwm sim thiab ob lub hlwb raug tsim.
Cov hlwb tsim nkag mus rau hauv interphase, uas yog luv heev lossis tsis tuaj.
Second meiotic division
Meiosis II muaj tib theem:
- Prophase II. Chromosomes ua denser, nuclear membranes ploj, thiab fission spindle pib tshwm (duab saum toj no).
- Thaum lub sijhawm metaphase II, kev tsim ntawm cov ntxaiv txuas ntxiv, thiab cov chromosomes nyob rau ntawm txoj kab sib faib.
- Anaphase II. Cov chromosomes tau ncab mus rau cov ncej ntawm tes (duab hauv qab).
- Telophase II. Nuclear daim nyias nyias yog tsim, lub cytoplasm yog muab faib nruab nrab ntawmob lub hlwb.
Nrog rau qhov kev faib no, tus naj npawb ntawm chromosomes tsis hloov, tab sis txhua tus ntawm lawv tsuas muaj ib chromatid (cov qauv tsev). Qhov no yog qhov tseem ceeb ntawm meiosis II. Cells yog tsim nrog ib tug haploid txheej ntawm chromosomes nyob rau hauv txhua (n).
Kev lom zem ntawm meiosis
Nws yog dab tsi, nws twb tau meej meej:
- Meiosis yog ib lub tswv yim zoo tshaj plaws uas ua kom muaj qhov sib xws ntawm karyotype (tus naj npawb ntawm chromosomes) ntawm cov tsiaj uas muaj nyob hauv kev sib deev.
- Vim yog ob qhov sib law liag ntawm meiosis, tus naj npawb ntawm chromosomes hauv gametes ua haploid thiab nws dhau los ua qhov laj thawj los rov qab diploidy thaum lawv sib koom ua ke (fertilize) nrog kev tsim cov zygote nrog tus thawj diploid karyotype.
- Nws yog meiosis uas muab cov khoom muaj sia xws li kev hloov pauv. Hauv prophase kuv - vim hla dhau, thiab hauv anaphase kuv - vim qhov tseeb tias homologous chromosomes nrog cov noob sib txawv tuaj yeem xaus rau hauv gametes sib txawv.
Dab tsi yog Crossover
Cia peb rov qab los prophase kuv ntawm meiosis. Nws yog nyob rau lub sijhawm no, thaum homologous chromosomes tau los ze thiab yuav luag daig ua ke, tias kev sib pauv ntawm lawv ntawm txhua qhov chaw tuaj yeem tshwm sim. Nws yog qhov kev pauv no hu ua hla dhau, uas txhais los ntawm lus Askiv (hla dhau) txhais tau tias hla lossis hla.
Hauv lwm lo lus, ib feem ntawm chromosome tuaj yeem hloov chaw nrog tib seem ntawm lwm tus chromosome los ntawm tib khub. Qhov no mechanism muab recombinative genetic variability ntawm cov kab mob. shufflingCov noob ua rau muaj kev sib txawv ntawm ntau hom hauv ib hom.
Lub voj voog thiab meiosis
Nyob ntawm theem twg ntawm lub neej voj voog meiosis tshwm sim, muaj peb hom meiosis hauv biology:
- Initial (zygote) tshwm sim tam sim tom qab fertilization hauv zygote. Hom meiosis no yog qhov zoo rau cov kab mob uas muaj feem ntau ntawm cov theem haploid hauv lub neej voj voog. Cov no yog cov fungi (ascomycetes thiab basidomycetes), qee cov algae (chlamydomonas), protozoa (sporozoa).
- Intermediate (spore) meiosis tshwm sim thaum lub sij hawm tsim spores nyob rau hauv cov kab mob nrog ib tug uniform alternation ntawm diploid thiab haploid daim ntawv. Cov no yog cov spores siab dua (mosses, qws mosses, horsetails, ferns), gymnosperms thiab angiosperms. Ntawm cov tsiaj, hom meiosis no yog yam ntxwv ntawm marine protozoa foraminifera.
- Kawg (gametic) meiosis yog muaj nyob rau hauv tag nrho cov multicellular tsiaj, fucus seaweed thiab ib co protozoa (ciliates). Nyob rau hauv cov kab mob no, lub diploid theem predominates nyob rau hauv lub neej voj voog, thiab tsuas gametes muaj ib tug haploid txheej ntawm chromosomes.
Summarize
Cov tub ntxhais kawm tau paub txog qhov tseem ceeb ntawm meiosis hauv qib 6 thaum kawm protozoa, algae, thiab txav mus rau kev kawm txog cov nroj tsuag biology. Lub tswv yim tseem ceeb ntawm kev biology dav dav thiab cov txheej txheem ntawm kev tsim cov kab mob hlwb (gametes) tso cai rau peb nkag siab txog kev sib koom ntawm txhua lub neej hauv peb lub ntiaj teb, kom nkag siab txog ntau yam kev ua neej ntawm cov nroj tsuag thiab tsiaj txhu.
Ntxiv mus, nws yog meiosis uas peb yuav tsum yogua tsaug rau qhov sib txawv intraspecific ntawm cov tsiaj hom Homo sapiens. Thaum kawm txog biology hauv cov chav kawm tom ntej, cov tub ntxhais kawm txuas ntxiv mus kawm cov theem ntawm kev sib deev sib faib, thiab thaum lawv paub txog cov noob caj noob ces, cov cai ntawm kev sib txawv thiab kev hloov pauv.
Kawm txog cov txheej txheem ntawm ntau lub xov tooj ntawm tes faib ua rau peb nkag siab txog qhov tshwj xeeb thiab kev tsim nyog ntawm cov cai ntawm xwm, uas tau tsim ntau txhiab xyoo ntawm kev hloov pauv ntawm ib lub ntiaj teb ntawm lub hnub ci. Thiab peb muaj hmoo tau yug los rau nws.
