Malumoti ohirin
Home / Biologiya / DAVRI YAKUMI TAQSIMSHAVII MEYOZI

DAVRI YAKUMI TAQSIMSHAVII MEYOZI

Dar profazai 1 torhoi khromatin (khromosoma) dar zeri mikroskopi rushnoi namoyonand va shakli spirali dorand.

Dar hamin davra, agar binoishi mikroskopro kalon kunem, malum megardad, ki har yak khromosoma du khromatin doshta onho bo ham ba sentromerashon chaspidaand. Hromosomahoi gomologi bo ham nazdik va nuqtahoi bo ham muvofiqi onho jafs meshavand. Dar meyoz ravandi jafsshavii qismhoi bo ham muvofiqi khromosomahoi gomologiro konyugatsiya menomand. Dar rafti konyugatsiya khromosomahoi gomologi, ki har yaki on az du khromatid iborat ast, bo ham nazdik meshavand (masofai bayni onho az 120 nm ziyod nest).

6-7

Albatta, khromosomaho pahlu ba pahlu nakhobida, bo yorii torhoi safedavi, ki dar qisme az onho joyhoi kholi mavjud ast, yakdigarro nigoh medorand. Torhoi har du khromosoma dar shakli zireh bo hamdigar payvast shudaand (rasmi 6.6).

Bo yorii chunin chaspakho (kuprukcha) khromosomahoi gomologi metavonand duru daroz dar holati konyugatsiya nigoh doshta shavand. Jufti khromosomahoi bo ham nazdikshudaro bivalent (az lotini bi-duchand) yo tetrada (yunoni tetro – chortogi) menomand. Dar oyanda dar bayni khromosomae, ki bivalentro tashkil mekunad, ivazshavii qismhoi yakkhelai khromosomahoi gomologi, yane genhoi yakkheladoshta ba amal meoyad. In ravandro chillikshavi menomand (rasmi 6.7). Dar okhiri profaza dar bayni khromosomahoi gomologi quvvai teladihanda paydo shuda, avval az qismi sentromer (kashishkhuranda) va ohista ba digar qismho tasir merasonad. Hromosomaho tanho dar joyhoi chillikshuda bo ham aloqamand meshavand (rasmi 6.8)

Dar metafazai 1 spiralshavii khromosomaho ba nuqtai balandtarin rasida, onho kutoh va gafs meshavand. Hromosomahoi yakjoyashuda (konyugatsiyashuda) dar khati 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.

Dar anafazai 1, dushhoi 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. Hullas, badi taqsimshavii yakumi meyozi dastai khromosomaho barobar (1n, 2s) ast.

Dar telofazai 1 dar muddati kutoh pardai yadroi paydo meshavad. Az sababi on ki khromosomahoi alohidai hujayrahoi dukhtari gaploidiand va miqdori KDN-i duchandai onho nigoh doshta meshavad, binobar in, dar (interkinez)

bayni taqsimshavii yakumin va duyumini meyozi duchandshavii KDN ba amal nameoyad. Hujayrahoe, ki dar natijai taqsimshavii yakumi meyozi hosil shudaand, bo khosiyat va tarkib az khromosomahoi padari va modari, hamchunin bo genhoi khud farq mekunand. Masalan, hamai hujayrahoi jismi odam, az jumla, hujayrahoi avvalin (ibtidoi)-i jinsi, 46-khromosoma dorand.

Az in miqdor khromosoma 23-to az tarafi modar va 23-to az tarafi padar ast. Badi taqsimshavii yakumi meyozi dar spermatozoidho va oositho faqat 23 khromosoma joy dorad, yane az har yak jufti khromosomahoi gomologi yaktogi. Lekin dar natijai tasodufan kashish khurdani khromosomahoi padari va modari dar anafazai I hujayrahoe paydo meshavand, ki kombinatsiyai gunoguni 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 (kombinatsya) khelo ziyod ast. Agar ivazshavii (dodu girifti) khromosomahoi gomologiro ba nazar girem, on goh malum megardad, ki har hujayrai hosilshuda behamtost (yagona va takrornashavanda), zero doroi dastai genhoi takrornashavanda meboshad. Hamin tavr, meyoz asosi tagyirpazirii genotipi va kombinativi ast.

Загрузка...

Dar boramon

Инчунин кобед

GENETIKAI JINS. MEROSGUZORII ALOMATHOI BO JINS CHASPIDA

Masalai inkishof va paydoishi farqiyati jinsi, mekhanizmi muayyan kardani jins, nigoh doshtani tanosubi muayyani jinsi …