CUESTIONARIO DE PARTICIPANTES

in the sheep , bu t that th ese di fferences were very small . The accuracy of vi sual e s ti ma ti on of chromo s ome l ength and p o s i t i on , as shmm in karyotypes , proved to be low at p o s i t ions b el m·r chr omos ome

7.

There was frequ ently di ssimi larity ir1 l ength b ehJeen homol ogues , especi ally in chromo some

1 .

Gimenez-Ma r t in and Lopez

-

Saez

( 1966 )

found that the larg e s t chromos ome had a subm edian centromere , t h e s e cond chrom o s ome of almo s t

trw s ame l ength a subm edian o r medi an centrom ere and the thi rd; vri th a

median centromerc) d i ff ered in si z e by a greater amount than the difference ivhi ch exi s t ed b ehreen the fir s t hvo chromosome s .

and NcLaren

( 1 967 )

and R o ca and Rodero

( 1 971 )

hm·rever , found tha t the s i z e o f chromo som e 2 uas mi dvray b etvreen that- of chromosom e

1

and

3 .

Dain

( 1 972 )

claimed that th e long arms o f the fi rst and second pai r s

o f m e tacentri c chromo some s and the fourth pair vrhi ch a r e acro centri c ,

were longer in rams than i n ewe s , and di s cu s sed her theory tha t these

observati ons a r e c o nsistent vli th the p r e s ence of male-determining genes

on the long arms of the fir s t t1vo pair s of auto somes . Dain' s

o b s e rvations wer e n o t in agreement 1·ri th , an<1 no reference vras made by h er t o , the 1>10 rk of Bru

�

re

( 1 966 )

o r B ru

�

r e and l'kLar en

( 1967 ) .

There was some variatj_ on b o th in position and morpho l ogy o f

s e condary cons t r i ct i ons . The maj ori ty v1e re found on aut os ome pai rs

1 ,

2 , 3

and

4

and_ the X chromosom e . Half o f the recorded s e c ondary con s tri c ti ons o ccu rred on the three pai rs of metacentri c chromosomes .

I t vms suggested

(

B ru

h

e ,

1966 )

that th e s e may be th e main nu c leolar

organi z er chrom o s omes in the sheep . Sub s equent evi den c e from

aut oradi ographi c and Gi emsa b anding s tu d i es has confirmed this suggesti on

(

Zartman and B ru

�

r e ,

1974 ) .

The various constrictions r e c o rded on the remainder of the a cro cen tric chromo some s did not suggest any means of di fferentiating these chromo s omes . Bru

�

re and McLaren

( 1967 )

noted an increase in the inci dence of s e condary c ons tri ctions when hypotoni c s o dium ci tra t e s o luti on was u sed ins t e a d o f Hanks balanced salt solution and suggested that thi s could be ass o ci a t ed vli th removal of cal cium from

'"'

the m edium during the hypotonic treatmen t .

The c entromere posi tion was n ever seen v ery c l early i n ei ther the metacentric o r acro centri c chrom o s om e s , althou gh i t app eared t o b e more central i n chromo s ome

3

than i n

1

or

2

(

Bru

�

re and llicLaren ,

1 967 ) .

Bru

�

re and McLaren

( 1 967 )

s tressed two morphologi cal feat�res

in the karyo type of the sheep not emphasi z ed by previ ou s au thors ; firstly , the p res ence of c l ear, sh ort arms on th e X chromo s ome , and s econdly the su'ometacentri c nature of th e Y chromo some . The X

chromosome whi ch was the largest of the acro centric chromo somes had mu ch more c l early defined short arm s than those o ccas i ona l ly s e en on

the other a c rocentri c chromos ome s.

B1�

�

re

(1 966 )

found that the modal diploid numb er o f

chromo some s

( 54 )

was pres ent in

87 . 44

p e r cent o f cells c ounted from a total of

1 831 .

Later , in a compari son of chromo some counts o f

22

normal sh eep wi th five fr eemar ti n sheep ,

Bru�re ( 1 967 )

r ep o r ted a signi fi cant increas e in bo th hypomodal and hypermodal ce l l s "l'ii th

increasing

age .

He su gges t ed th at simi lar biologi cal m echanisms to

those whi ch contribu t e to age aneuploidy in man (Jacob s , C ourt B rovm and Dol l ,

1 961 )

could a l s o app ly to the sheep .

Gerneke

( 1 967 )

found a diploid numb er o f

54

chromo somes in

the Merino , Karaku l and Afrikaner breeds . H e <ms unab le to decide whi ch o f the acrocentri c c hromo somes was the X , bu t his des crip tion of the Y chr oJLo some wa s in agreement wi th that of Bru

�

re

(1 96 6 ) .

Althou gh no features comparab le to the sat e ll i t es s e en in human acro cen tri c chromo some s ( Ferguson-Smith et

1 962 ;

Fergv.s on­ Smith and Handmaker ,

1 961 ; 1 963 )

w ere record ed hy Bru

�

re

( 1 966 ) ,

what he interpreted as ass o ci ati ons b e tween acrocentr i c chr omo s omes were seen. As soci ati ons b etween acrocentri c and metacentri c

chromosomes Here also re co rded by Bru

�

re

(1 96 6 )

but he c ould not dravr any c orrel afi ons between th ese as s o ciat ions and s e c ondary

constri ctions . Ferguson-Smi th and Handmaker

( 1 963 )

found that

excessive treatment 1-ri th hyp o tonic solution appeared to reduce the frequency of chromosome ass o ci a tions . Likev1i s e in the she ep , B ru

�

re

( 1 9 6 6 )

suggested tha t the s a t e l l i t e associations in the sheep mi gh t b e more compl ex and de licat e than i n man and mi ght b e di s rupted by techni cal manipu lation .

The diploi d chr omosome numb er , s ex chrom o some complement and chromosome morphology of the dome sti c sheep ( Ovi s ari e s

)

have b een

e s tab li shed and are independent of the b reed studi ed . Using

conventi onal method s , i dent if i cation of the individual chromo some s in the karyotyp e i s di ffi cul t a s many are morphologi cally simi lar . I t i s

now po s sib l e t o identi fy every chromosome in the s heep' s complement u sing Quinacrine fluores cenc e t echni qu es

(

Evans , Buck land and Sumner ,

1 973 ;

Hansen ,

1 973 ,

a ) and Gi emsa ban ding techni ques ( Evans e t

1 973 ;

Zar tman and

Bru�re , 1 974 ) .

Th ese techni cal advanc es shoul d

aid the de tection o f chromosomal abnormalities i n sheep . suggestion is di scusse d fu rther i n Chapter

Vo

I I . 2 TAXONOI'U C Al\TD EVOJ_,U'J'I OEARY IW.lESTI G AT I ONS _{IN SHEEP}

This

Chromosome studie s have recent ly been applied to taxonomi c and evolu ti ona ry i nvestigations i n sheep ( Hurster and Beni r s chke ,

1 968 ;

Dain ,

1 970 ;

Nadler ,

1 971 ;

Nad l e r , Lay and Hassinger ,

1 971 ;

Evans e t

1 973 ;

Nadler , Ho ffmann and Vloolf,

1 973) .

Di fferent t ypes of wi ld and dome s t i c sheep have been shovm to b e characteri z ed by di fferent diploi d chromosome numbers ( 2n ==

54 , 55 , 5 6 , 57

and

58 )

-.ri th in all cases a fundamen tal number or the numb e r of chromosome a rms ( Na tthey ,

1 945 )

of

60

(Nadler

1 971 ; 1 973 ) .

Examinati on of two other species

b elonging to the family Bovi d ae , the goa t hi rcus ) and the ox

( Bos as lre l l as

the

sheep has sh mm tha t although the chromosome numb e r is variab l e , the fundamental numb er ( N .

F. )

is remarkab ly constant ,

varying behreen

58

_{and 62 in th e ma .jori ty of species, (l·lurster a nd}

B enirschke ,

1 968 ) .

. This has b een regarded as good evidence tha t the chi ef mechani sm o f karyo typ e evolution in the Bovi dae is by Rob er tsonian

translocation ( Vlu rster and Beni rschk e ,

1 968 ) .

This vi ew is suppor ted by Evans et al .

( 1 973 )

who used modern ban ding techniqu8s to s tu dy chromosome homologi es as well as c entromeri c hetero chromatin i n the ox ,

goa t and sheep . These authors consi der hovrever that band i ng t echniqu es

are not ab l e to gi ve an unequivocal indication of the direction of evolu tion ( Evans et

1 973 ) .

Nadler e t a l .

( 1 973 )

suggested t hat although Rob er tsonian changes du e to centric fusions b ehreen acrocentri c chromosomes migh t b e responsible for changes in karyotyp e i n sheep from 2n ==

58

to 2n ==

54,

i n certain popula tions centri c fission could have occurred to raise the chromosome number .

I I .

3

SHEEP x

GOAT

HYBRIDS

The p rob l em of hybri di sa tion of she ep and goa ts has int erest ed many vrorkers in the fi elds of a ni maJ. bre eding and reproductive physiology

(Hancock , McGovern and S tamp ,

1 968 ;

r1cGovern ,

1 969) .

Inab i li t y to

LIBRARY MASSEY U �-l:VERSITY.

pro du c e viab le hybrids l ed to i nvest igations i nto the cyto logical

In document TítuloEvaluación de los conocimientos de enfermería ante el manejo inicial, movilización e inmovilización del paciente politraumatizado en el Servicio de Urgencias del Complejo Hospitalario Universitario de A Coruña (página 41-55)