DAVRAI INKISHOFI JANINI

Aksariyati hayvonoti serhujayra qati nazar az murakkabii sokht, zinai inkishofi janinro az sar meguzaronand. Davrai janini ba se marhila judo meshavad: taqsimshavi (porashavi) gastrulyatsiya va organogenez (inkishofi uzvho).

Inkishofi organizm az davrai yakhujayragi ogoz meyobad. Tukhmi bordor – janin – zigota, ki organizm dar on vaqt dar marhilai avvali davrai inkishof ast, dar natijai payi ham taqsim shudani organizmi yakhujayra ba organizmi ser hujayra tabdil meyobad. YAdroi zigotae, ki badi bordori binobar omekhta shudani nutfa va hujayratukhm paydo megardad, bad az chand diqiqa ba taqsimshavi shuru mekunad va hamrohi vay sitoplazma niz taqsim meshavad. Hujayrahoi paydoshuda az hujayrahoi organizmi kalon farq mekunand va onhoro blastomerho (az yunonii blastos – janin, meros – qism) menomand.

Dar vaqti taqsim shudan hajmi blastomerho kalon nameshavad, baroi hamin hamchunin ravandi taqsimshaviro porashavi menomand. Joi sitoplazmai qatshuda, ki dar natijai taqsimshavi ba du qism judo meshavad, juyaki porashavi nom giriftaast.

Dar misoli neshtarshaklon porashavii yake az namoyandagoni oditarini hayvonoti khordadorro dida mebaroem (rasmi 7.1). Juyaki yakumi porashavi, ki dar hamvorii meridiani, joygir buda, du qutbro bo ham payvastaast, zigotaro ba du hujayrai yakkhela taqsim mekunad. Inro zinai dublastomeragi menomand.

Juyaki duyumin niz meridiani buda, nisbat ba juyaki yakum ba tavri perpendikulyar joygir ast va hardu blastomerhoi taqsimshudaro az digar taqsim karda, chor blastomeri ba ham monand paydo meshavand.

Juyaki digar, yane porashavii seyumin ba tavri arzi surat megirad. On az khati markazi bolotar joygir buda, har chor blastomerahoro taqsim va hasht hujayra hosil mekunad. Sipas, guruhhoi taqsimshavanda pai ham ba faoliyat ogoz karda, yakdigarro ivaz menamoyand. Bo ziyod shudani miqdori hujayraho, taqsimshavii onho az hamdigar farq mekunand. Hamin tavr, blastomeraho tadrijan az markazi janin dur shuda javf (kovoki) ba vujud meorand. Dar okhiri davrai porashavi janin shakli hubobchahoro girifta, qabati hujayrahoi boloi qabati duyum khobidaro tashkil medihand.

Javfi janin ba muhiti beruni robita doshta, bo surokhihoi bayni blastomeraho meguzarad. Vale dar natijai joygirshavii zichi blastomeraho robitai javf bo muhiti beruni mahdud megardad. In javfro javfi yakumi jism yo blas tosela menomand.

Porashavi bo paydo shudani janini yakqabatai serhujayra, ki onro, blastula menomand, ba okhir merasad. Dar hujayratukhmi qurboqqa zardi nisbat ba hujayrahoi neshtarak (lansetnik) beshtar buda, asosan dar qutbho joygir shudaast va ba tarzi taqsimshavii on tasir merasonad.

Taqsimshavii hujayratukhm dar qurboqqa purra va nobarobar meguzarad. Du juyaki avvali meridiani tukhmro ba chor blastomerai yakkhela taqsim mekunad. Juyaki seyumini arzi boshad, dar jonibi qutbi gayrinashvi, ki dar on jo zardi kam ast, joygir shudast. Dar natija blastomerahoi paydo shuda, ba andozai khud az hamdigar farq mekunand (rasmi 7.1).

Dar mavridi duru daroz taqsim shudani hujayra hujayratukhmhoe, ki zardii kam dorand, hajman khurd meshavand. Dar khazandagon ravandi porashavi bo paydo shudani blastula, ki az blastulahoi neshtarshaklho farq mekunad, khotima meyobad. Devorai blastulahoi obkhokiho niz yakqabata buda, onro blastoderma menomand. Vay az chand qabat hujayrahoi makhsus iborat ast. Javfi avvalini jism khurd buda, ba jonibi qutbe, ki hujayrahoyash zardii kam dorand, aniqtarash ba qutbi gayrinashvi mayl mekunad.

Dar hujayratukhmi parrandagon porashavi bo tarzi digar meguzarad (rasmi 7.1). Sitoplazmai ozod, ki az zardi judost hamagi 1% hajmi umumii hujayratukhmi murgro tashkil medihad. Agar ba tukhmi murg nazar kunem, dar yak qutbi  on, ki zardi joy dorad dogero mebinem. Blastula yo lalichai janin, ki dar natijai porashavii qismi sitoplazmai az zardi judo paydo shudaast, doroi yadro meboshad. Dar nesh tarshaklho, obkhokiho, parrandagon, hamchunin dar hayvonoti digar andozai blastomeraho dar zinai blastulaho bo andozai zigota barobar ast. Ba iborai digar, dar taqsimshavii mitozii zigota va blastomeraho hujayrahoi dukhtari inkishof nameyoband, andozai onho to ba andozai hujayrahoi modari namerasad va hajmi blastomeraho dar natijai taqsimshavii mutassil khurd megardad.

CHunin khususiyati taqsimshavii mitozii blastomeraho dar inkishofi tukhmi bordorshudai hamai hayvonot ba mushohida merasad. Porashavi doroi khosiyathoi digar niz meboshad. Masalan, hamai hujayrahoi blastulagi dastai khromosomahoi diploidi va sokhti yakkhela doshta, az hamdigar ba miqdori zardi farq mekunand. In guna hujayrahoro, ki alomathoi makhsus nadoshta, baroi ijroi yagon vazifai muayyan mutobiq nashudaand, hujayrahoi nomakhsus menomand. Hosiyati digari porashavii blastameraho kutoh budani sikli mitozii onho nisbat ba hujayrahoi organizmi kalon meboshad. Dar onho davrai interfaza kamtar davom karda, faqat duchandshavii KDN ba amal meoyad.

YAke az jihathoi muhimi porashavi omekhta nagardidani sitoplazmai zigota meboshad. Hamai in tafovvuthoe, ki dar sokhtori sitoplazmai tukhm dida meshavad, asosi tafriqa shudani hujayraho buda, dar natijai on az hujayrahoi gunoguni blastameraho in yo on uzvu boftaho paydo meshavand.