A. RESTING NUCLEUS 



CHROMOSOMES THREAD-LIKE 

 AND SCATTERED THROUGH- 

 OUT NUCLEUS, NOT VISIBLE 

 AS DISTINCT CHROMOSOMES 



B. LEPTOTENE NUCLEUS 



CHROMOSOMES BECOME 

 EVIDENT AS DISTINCT 

 STRUCTURES 



NUCLEOLUS 



C ZYGOTENE (SYNAPTENE) 

 NUCLEUS 



HOMOLOGOUS CHROMOSOMES 

 BEGIN TO SYNAPSE,! E, 

 UNITE IN PAIRS 



D PACHYTENE NUCLEUS 



CHROMOSOME PAIRS BECOME 

 CLOSELY ASSOCIATED AND 

 EACH PAIR SHORTENS AND 

 APPEARS MUCH THICKER 

 EACH"CHR0M0S0ME" IS MADE 

 UP OF FOUR CHROMATIDS,! E . 

 IT IS A TETRAD DUE TO THE 

 FACT THAT EACH HOMOLOGOUS 

 CHROMOSOME WHICH ENTERED 

 INTO THE ORIGINAL UNION HAS 

 DIVIDED LONGITUDINALLY INTO 

 TWO CHROMATIDS 



E. DIPLOTENE NUCLEUS 



THE CHROMATIDS OF EACH 

 TETRAD SHOW A REPULSION FOR 

 EACH OTHER AND THE TETRAD 

 AS A WHOLE BEGINS TO OPEN 

 UP THE CHROMATIDS ALSO 

 BECOME MORE ATTENUANT, 

 PARTICULARLY IN THE OOCYTE 

 WHERE THE NUCLEUS EN- 

 LARGES AND FORMS THE 

 GERMINAL VESICLE IN WHICH 

 THERE IS A LARGE AMOUNT 

 OF NUCLEAR SAP THE 

 CHROMATIDS BECOME VERY 

 LONG AND MAY SHOW LATERAL 

 LOOPS 



F GERMINAL VESICLE 



YOUNG GERMINAL VESICLE 

 OF CAT OOCYTE IN TRANSI- 

 TION FROM THE MORE 

 TYPICAL DIPLOTENE CONDI- 

 TION INTO THE MATURE 

 GERMINAL VESICLE SHOWN 

 BELOW 



G GERMINAL VESICLE 



THE GERMINAL VESICLE STAGE 

 OF THE OOCYTE NUCLEUS OF 

 THE CAT IN WHICH THE 

 V/ DIPLOTENE CHROMATIDS ARE 



ELOMGATED AND DO NOT 

 TAKE THE BASIC STAINS 

 READILY 



H GERMINAL VESICLE 



GERMINAL VESICLE OF 

 DEVELOPING SHARK OOCYTE 

 SHOWING MANY NUCLEOLI 

 AND "LAMP-BRUSh"cHR0MO- 

 SOMES 



I GERMINAL VESICLE 



GERMINAL VESICLE OF 

 AMPHIOXUS OOCYTE WITH 

 LARGE NUCLEOLUS!?) 



Fig. 71. Certain aspects of the oocyte nucleus during the meiotic prophase. (A-G) 

 Chromatin and nuclear changes in the oocyte of the cat up to the diplotene condition 

 when the germinal vesicle is fully developed. (After de Winiwarter and Sainmont, Arch, 

 biol., Paris, 24.) (H, 1) Germinal vesicle in the dogfish, Scyllium canicula, and in 

 Amphiuxus. (After Marechal, La Cellule, 24.) Observe the typical "lamp-brush" chromo- 

 some conditions in the germinal vesicle of the shark oocyte. These lamp-brush chromo- 

 somes are developed during the diplotene stage of meiosis by great attenuation of the 

 chromosomes and the formation of lateral extensions or loops from the sides of the 

 chromosomes. 



136 



