Educación bilingüe y biliteracidad - Enseñanza de la lectura y de la escritura en inglés en los

4. RESULTADOS

4.4. Educación bilingüe y biliteracidad

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bj,armed

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" \..0 --..J

( E

)

Dogs

C en t ri c f'u s i or. o f chromo s orn8s

has

b een o b s e rved

at

l eas t tllrue d.i fi'e:r·-:mt o c casi ons in the dog. '11vTO c a s e s

o f

apparent centri c fusi o::1 b ehreen t;-ro au tosomes have b een

repo:!:'ted

i n dogs wi th c ong�mi tal

abno rmo. l i. t i c s ( Shive $

Ha:ce and Pat t e rson ,

1965;

Har e , Wi lkins on , hcFeely and

Riser, 1967) and

a third cas e i n a

pheno tY]li ca l ly normal doe ( Jila _and _Gi_l_r_no_r_e_,

1 971 )

( iii )

RCBETI'J'SONI AY

TR/IJTS J,OC A TH JI;:3 tfJAN

The

human

kary o type ha s b een s tud i ed mo r e ext ensiv ely than that of any o tbel' marcma l . Much _{o f thi s} _{s tuQy} _has _{b een}

prompted by

th e v a ri e ty of c l i ni ca l condi t i ons :ff.'eg_uen tly found to b e a s s o c ia t e d vfi -t,h _anabno rmal _{karyo typ}_e_. _{R o b er t;;oni:':'.n trans l c ca ti on s}

are the mo s t conl!Lon typ e o f tran s l o c a t i on r epor ted j_n man

and

a:!:'e

r

es ent in

about

0 . 5 p er cen t of the popu la t i on ( C ourt _{Bro>m ,}

1967).

The human karyo typ e contai ns only tl1 0 grou ps (

g

roup D and group G )

of acro cent r i c chr omo some s ( '1 0 out of

a

to tal of

46

chromos om es ) . I n c on trast t o the a c ro centri c chrom o s omes o f th e domestic animals , human acro centri c chrom o somes have vi sib l e s a t e ll i tes , b e lieved to consi st of eu chromatin , on their short arms ( Ferguson- Smi th

and

Handmaker, 1 96 1 ; 1 963 ) . The c a t elli ted ch romo s o�e s o f rnQn a s s o ci a t e

short arm

to

short arm i n mi t o ti c metapha

s

e preparati ons ( Fergu s on-

Smi th and

Handiilaker, 1961 ; 1963;

C oh en

and Shavr, 1967; Galperin,

1968;

C o oke ,

1972)

and a l s o du_r_i_n_g_{mei o s i s} _{( Fergus on-Smi th ,}

1964).

From thi s ass o ciati on i t has b een sugees

t

ed that t hes e chromo somes are non-di s j uncti on pron e ( Ohno , Truj i llo , Kaplan and Kinos i ta ,

1 961 ; Galperin, 1968)

and Ohno et al .

(1 961 )

p o s tu lated that i n creas ed

sat elli te a s s o ciati on mi

g

ht a l so be r ebt orl fo th e

format i on

o f

tran s lo ca.ti ona b e tween t h e a c r ocentri c chromosome s .

Breakages

could possib ly o ccur more easi ly i n the a t t enuated s econdary co nstri ction areas and t h e chance of a transloc ation o c cu rr.ing would. be grea t er

the broken

ends of di fferent memb ers w ere i n proximit_y

in

the nu c l eo lar regi on .

Three types of Rob erts oniar" tr.::tn s l o cation have b e en repo rt ed i n man ; b eh1een memb ers o f the D group of chromo s omes

( 1 3, 1

t� an cl 1

5 )

D/ D o r t ( DqDq )

b e tween memb ers o f the G group o f chromo somes ( 2 1 and 22 ) G/ G o r t ( 2 1 q22q ) an d

b etw een m emb ers of b oth groups D/ G o r t ( Dq Gq ) .

The D/D trans l o c a t i o n :!_ s th e mos t colli!lon , CJCC',; rring i n ab out on e in 1 , 000 adults in th e g ener_al F'Pulati on

(Cou::.:-t

B rown :

1 967 ) . I t i s a r.1etaccntri c t ranslocat i o n , fami lial a11cl c:arri ers of it produ c e o ffspring whi ch a re

either

n o rmal , balanced carri ers , or tri s omi c fo r a D group c h romo s om e . Apart from the t_ri_{s o}_m_i_c stat e ( �ayl or , 1 9 68 ) there app ears to be li t t l e evi denc e o f

pheno t ypi c abnormali ty in ba lanc ed D/D c arri ers . Individua ls 1·rho

are tri somi ::: for a D chromo s ome ei ther may b e aborted ( Lu cas , 1 96 9 ; Dhadi a l ,

I1achin

and Tai

t ,

1 970; Kaj i i , Ohama , _{Nii kavra} _{Ferri er}_and

Avi ra chan , 1 97 3 ) or b orn a live bu t vri th s ev ere congeni ta l mal formati ons ( Gi annelli , 1 96 5 ; C ourt Brown , 1 967 ; Tayl o r , 1 968 ) . Kj e s s le:r ( 1 964 ) o.es cribed a subferti l e man -vri th a D/D t rans l o cati on , but the ass o c i a t i on j_ f any wi th s t eri l i ty , was no t c lear .

Regular mongolis_m i n man i s as s o ci a t ed 1vi th the p r e s ence of an additi ona l acrocentri c chromo som e of the G group and i s referred t o a s tri s omy G o r tris omy 2 1 . I n thi s case the mon gol

has 47 chromo somes i nstead o f the normal 46 . Hovrever approximat e ly

two t o fi ve p e r c en t of a ll mongo l o i d i ndivi duals have 46 chrom o s omes

but carry the ex tra chromo s ome in the form o f a t ransl o c a t i o n . The c omm onest transl o c&tion i s b e t.1-r e en _{a m embe r of the D group and}

chromosome 2 1 ( D/ G ) and l e s s frequent ly b e tween _{h1o group} _G

chromosomes .

Behv e en 2 5 and 5 0 p e r c ent o f trans l ocation mongo l s have i nh e ri ted the trans l o cati o n chromos ome from a parent ( Gi ann e l l i , Hamerton and. C a rt er , 1 965 ; C ourt Broim , 1 967 ) I·Ihi le in the r ecnai nder

the _{trans lo cati o n has ari s en d e n ovo .} Th e _{parent in cases vihere} the chi ld has inh eri ted th e trans l ocati o n chromosome, i s a

phono typical ly normal balanced translocation carri er wi th

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