Dar profazai 1 torhoi khromatin (khromosoma) dar zeri mik- roskopi rushnoi namoyonand va shakli spirali dorand. Dar hamin davra, agar binoishi mikroskopro kalon kunem, malum megar- dad, ki har yak khromosoma du khromatin doshta, onho bo ham ba sen- tromerashon chaspidaand. Hromosomahoi gomologi bo ham nazdik va nuqtahoi bo ham muvofiqi onho chafs meshavand. Dar meyoz ravandi chafsshavii qismhoi bo ham muvofiqi khromosomahoi go- mologiro konyugatsiya menomand. Dar rafti konyugatsiya khromo- somahoi gomologi, ki har yaki on az du khromatid iborat ast, bo ham nazdik meshavand (masofai bayni onho az 120 nm ziyod nest).
Albatta, khromosomaho pahlu ba pahlu nakhobida, bo yorii torhoi safedavi, ki dar qisme az onho choyhoi kholi mavchud ast, yakdigarro nigoh medorand. Torhoi har du khromosoma dar shakli zireh bo hamdigar payvast shudaand .
Bo yorii chunin chaspakho (kuprukcha) khromosomahoi gomolo- gi metavonand duru daroz dar holati konyugatsiya nigoh doshta shavand. Jufti khromosomahoi bo ham nazdikshudaro bivalent (az kalimai lotini I-duchand) yo tetrada (yunoni 1e1go – chortoi) me- nomand.
Dar oyanda dar bayni khromosomae, ki bivalentro tashkil me- kunad, ivazshavii qismhoi yakkhelai khromosomahoi gomologi, yane genhoi yakkheladoshta ba amal meoyad. In ravandro chilikshavi me- nomand (rasmi 6.7). Dar okhiri profaza dar bayni khromosomahoi gomologi quvvai teladihanda paydo shuda, avval az qismi sentro- mer (kashishkhuranda) va ohista ba digar qismho tasir meraso- nad. Hromosomaho tanho dar joyhoi chilikshuda bo ham aloqa- mand meshavand (rasmi 6.8).
Dar metafazai 1 spiralshavii khromosomaho ba nuqtai ba- landtarin rasida, onho kutoh va gafs meshavand. Hromosomahoi yakjoyashuda (konyugatsiyashuda) dar khatti markaz joy megirand va sentromerahoi khromosomahoi gomologi ba jonibhoi muqobili qutbhoi hujayra menigarand (rasmi 6.8). Bo sentromeraho torhoi duk (akhromatin) payvast meshavand. Dar hamin davra miqdori khromosomahoro dar zeri mikroskop ba hisob giriftan nisbatan oson ast.
Az in miqdor khromosoma 23-to az tarafi modar va 23-to az tarafi padar ast. Badi taqsimshavii yakumi meyozy dar sper- matozoidho va oositho faqat 23 khromosoma joy dorad, yane az har yak jufti khromosomahoi gomologi yaktoi. Lekin dar natijai tasodufan kashish khurdani khromosomahoi padari va modari dar anafazai I hujayrahoe paydo meshavand, ki kombinatsiyai guno- guni khromosomahoi volidonro dorand. Masalan, dar yake az in hujayraho mumkin ast 3 khromosomai padari va 20 khromosomai modari, dar digarash 10 khromosomai padari va 13 khromosomai modari, dar seyumash 20 khromosomai padari va 3 khromosomai modari va gayra joygir shavad. Miqdori ehtimoliyati omezish (kombinatsiya) khele ziyod ast. Agar ivazshavii (dodu girifti) khro- mosomahoi gomologiro ba nazar girem, on goh malum megardad, ki har hujayrai hosilshuda behamtost (yagona va takrornashavan- da), zero doroi dastai genhoi takrornashavanda meboshad. Hamin tavr, meyoz asosi tagyirpazirii genotipi va kombinativi ast.
Dar telofazai 1 dar muddati kutoh pardai yadroy paydo me- shavad. Az sababi on ki khromosomahoi alohidai hujayrahoi dukh- tary gaploidiand va mikdori KDN-i duchandai onho nigoh doshta meshavad, binobar in, dar (interkinez) bayni taqsimshavii yakum va duyumi meyozy duchandshavii KDN ba amal nameoyad. Hujay- rahoe, ki dar natijai taqsimshavii yakumi meyozy hosil shuda- and, bo khosiyat va tarkib az khromosomahoi padary va modary, ham- chunin bo genhoi khud farq mekunand. Masalan, hamai hujayrahoi jismi odam, az jumla hujayrahoi avvalin (ibtidoy)-i jinsy 46 khromosoma dorand.Dar anafazai 1, kitfhoi khromosomaho az ham judo shuda, khromosomaho ba qutbhoi gunogun kashida meshavand. Hamin tavr, dar hujayrahoi dukhtari az har jufti khromosomahoi gomologi faqat yak khromosoma joygir meshavad. Miqdori khromosomaho du barobar kam shuda, dastai khromosomaho gaploidi ast, vale dar hamin holat har khromosoma az du khromatin iborat buda, miqdori KDN-i duchanda dorad. Hulosa, badi taqsimshavii yakumi meyozi dastai khromosomaho barobar (1p, 2s) ast.
Davrai duyumi taqsimshavii meyozi. In davra umuman ba taqsimshavii mitozi monand buda, tanho farq dar on ast, ki in hujayraho gaploidiand (1p 2s). Dar anafazai II sentromeraho (kashishkhurakho), ki khromatidhoi khohariro payvasta nigoh medo- rand, dar yak khromosoma taqsim meshavand. Az hamin vaqt khroma- tidho chun dar mitoz khromosomahoi mustaqili dukhtariro tashkil karda, ba qutbhoi bo ham muqobil ravona megardand. Bo khotimai telofazai duyum, ravandi meyozi ham ba okhir rasida, az yak hujay- rai ibtidoi (avvala)-i jinsi 4 hujayrai gaploidi bo dastai khromosomai 1p 1s paydo meshavad. Hamin tavr, mohiyati davrai rasish az on iborat ast, ki dar du davri taqsimshavii meyozi miqdori khromosomahoi hujayrahoi jinsi du barobar va miqdori KDN boshad, 4 barobar kam meshavad.
Mazmuni biologii taqsimshavii duyumini meyozy dar on ast, ki miqdori KDN bo miqdori khromosomaho barobar megardad (1:1). Dar fardhoi jinsi narina onho dar 4 hujayrai gaploidi, ki dar natijai meyozi paydo shudaand, joygirand va dar oyanda ba gametaho tabdil meyoband. Dar fardhoi jinsi modina dar na- tijai nobarobarii meyozi faqat yake az in hujayraho qobiliyati inkishof doshta, hujayratukhmro hosil mekunad. Se hujayrai di- gari dukhtari khele khurd buda, ba hissachahoi reduksioni tabdil meyoband va sipas mahv meshavand.
Mohiyati biologii paydo shudani yak hujayratukhmi tanho va nobud gashtani se oositi norasida, ki onhoro az nigohi genetiki hissachai reduksioni menomand, dar hujayra imkoniyati zakhira shudani moddahoi gizoii baroi inkishofi janin lozimro nigoh medorad. Vobasta ba miqdori zardi dar hujayratukhm gametahoi modina ba navho taqsim meshavand.
Dar neshtarshaklon zardi kam buda, on dar sitoplazma baro- bar pahn gardidaast, vale dar khazandagon va parandagon zardi bisyor buda, dar yak tarafi hujayra jam gashtaast. In qismro nashvi (gizodihanda) menomand. Qismi digar, ki dar on zardi kam ast va hujayra yadro dorad, qismi animali (az lotini ashtaNz – hayvon) menomand.
Testho
- Dar profazai yakumi meyozi khromosomaho kadom holatro az sar meguzaronand?
a) khromosomahoi gomologi bo ham jafs meshavand; b) az hamdigar dur meshavand; v) khromosomaho shakli tori dorand.
- Har yak khromosomai gomologi az chand khromatid iborat ast?
a) du; b) se; v) chor.
- Jufti khromosomaho bo ham nazdikshudaro chi menomand?
a) bivalent; b) sevalent; v) tetravalent.
- SHakli purrai spiralshavi dar kadom faza ba amal meoyad?
a) profazai I; b) metafazai I; v) anafazai I.
- Baroi chi dar metafaza khromosomaho kutoh va gafs meshavand?
a) dar natijai spiralshavi; b) dar natijai jafsshavi; v) dar natijai telakhurdan.
- Dar kadom faza khromosomaho ba qutbho kashida meshavand?
a) metafaza; b) anafaza; v) telofaza.
- Dar kadom faza pardai yadro va yadrocha az sari nav barqaror me- shavand?
a) anafaza; b) telofaza; v) interfaza.
- Davri duyumi taqsimshavii meyozy ba kadom taqsimshavi monand ast?
a) amitoz; b) endomitoz; v) mitoz.
- Dar rafti inkishofi spermatogenez (nutfagenez) chand gametai (nutfa) gaploidi paydo meshavad?
a) seto; b) chorto; v) shashto.
- Dar rafti inkishofi oogenez chand tukhmhujayra paydo meshavad? a) chor; b) du; v) yak.