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Hromozom

Posted by [email protected] on April 8, 2014 at 5:15 PM

Hromozomi su telašca karakterističnog oblika koja se u jedru mogu uočiti za vreme deobe. Najbolje se uočavaju za vreme metafaze / mitoze pa se tada i izučavaju i nazivaju metafazni hromozomi

Svaki metafazni hromozom se sastoji od:

 

dve sestrinske hromatide koje sadrže po jedan molekul DNK, i s obzirom da nastaju replikacijom, ti molekuli su potpuno jednaki po sadržaju gena; zato se hromatide nazivaju sestrinske;

centromere ili primarnog suženja koje spaja hromatide.

Pored ovih delova, specifičnih za sve hromozome, poneki hromozomi mogu imati i sekundarno suženje. Akrocentrični hromozomi u humanom kariotipu imaju to suženje.

Po položaju centromere u hromozomu razlikuju se:

 

metacentrični hromozomi, kod kojih je centromera postavljena medijalno, a p i q kraci su približno iste dužine. U obu grupu spadaju hromozomi: 1, 3, 16, 19, 20.

submetacentrični hromozomi, kod kojih je centromera postavljana nešto niže nego što je to slučaj kod metacentričnih, pa je p krak nešto kraći od q kraka. U obu grupu spadaju hromozomi: 2, 4-12, 17, 18, X.

akrocentrični hromozomi, kod kojih je centromera jako pomerena ka jednom kraju hromozoma, a p krak daleko kraći od q kraka. U obu grupu spadaju hromozomi: 13, 14, 15, 21, 22, Y.

telocentrični hromozomi, kod kojih se centromera postavljena na samom kraju hromozoma, odlikuje ih odsustvo p kraka. Nalazi se samo kod životinja.

Broj hromozoma je stalan i karakterističan za svaku biološku vrstu i naziva se kariotip.

 

Telesne (somatske) ćelije imaju diploidan (grč. diploos = dvostruk) broj hromozoma [obeležava se kao 2n]. Telesna ćelija čoveka ima 46 hromozoma ili dve garniture po 23 hromozoma, pri čemu jedna garnitura potiče od majke, a druga od oca pa se tako obrazuje 23 para homologih hromozoma.

 

Polne ćelije ili gameti [kod čoveka su to spermatozoidi i jajna ćelija] sadrže upola manji broj hromozoma u odnosu na telesne ćelije, nazvan haploidan [grč. haploos = jednostruk] - obeležen kao n. Ako telesna ćelija ima dve, onda će polna ćelija imati jednu garnituru hromozoma. Broj hromozoma u polnim ćelijama čoveka je 23.

http://sr.wikipedia.org/sr-el/%D0%A5%D1%80%D0%BE%D0%BC%D0%BE%D0%B7%D0%BE%D0%BC


Categories: Zoologija, Botanika

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