JUSTIFICACIÓN DE DIFERENCIAS

‘We k n o w t h a t c h i l d r e n m o s t r e s e m b l e t h e f a t h e r o n l y w h e n t h e m o t h e r

HAS A VERY LIVELY IMAGINATION AND LOVE FOR OR FEAR OF THE H U SBA N D .’

L avater, 18^^ c e n tu iy .

The id e a of fam ily re se m b la n c e in a p p e a ra n c e is n o t n ew or

u n u s u a l. The p ro b lem of o b tain in g a q u a n tita tiv e e s tim a te of th e

re se m b la n c e b etw een sib s c a n be d a te d b a c k to 1875 (G alton 1875)

a n d co rre latio n s tu d ie s of tw in s have c o n tin u e d sin ce for a n extensive

rep e rto ire of c h a ra c te ris tic s b o th q u alitativ e a n d q u a n tita tiv e (Eaves

et al 1999; B u rk e a n d Healy 1993).

Very few facial fe a tu re s h av e b e en d o c u m e n te d a s b ein g

in h e rite d in a sim ple m a n n e r following a M endelian p a tte r n of

in h e rita n c e . A lthough th ro u g h fam ily re c o rd s a n d p h o to s it is

p o ssib le to tra c e p a rtic u la r fe a tu re s th ro u g h th e g e n e ra tio n s, th is is

p a rtic u la rly th e c a se in royal fam ilies w h ich a re often well

d o c u m e n te d for m a n y g e n e ra tio n s th ro u g h p o rtra its a n d sc u lp tu re s .

H ow ever m o st royal fam ilies th ro u g h th e ag es h av e a d v o ca te d a form

b e e n u n c o m m o n for first co u sin , a u n t-n e p h e w , a n d u n c le -n ie c e

m a rria g e s to occur.

P o rtra its of E u ro p e a n m o n a rc h s often d isp lay strik in g

sim ilarities b etw een re la te d m em b e rs of th e fam ily, p o ssib ly reflecting

th e re d u c tio n in g enetic h etero g en eity . From th e 13^^ to th e 20^^

c e n tu ry th e H a b sb u rg royal fam ily w as pow erful in E u ro p e. A rtists

u n w ittin g ly d o c u m e n te d th e effect of su ccessiv e g e n e ra tio n s of

in b re e d in g in th is fam ily th ro u g h p o rtra its (Hodge 1977). T he

p h e n o ty p e s p o rtra y e d on c an v a s aid ed co m p ilatio n of a n ex ten siv e

H a b sb u rg fam ily pedigree w ith 40 9 m em b ers, 23 g e n e ra tio n s a n d 13

fam ilies (Wolff e t al 1993). T his pedigree d isp lay s one of very few

ex am p les of sim ple a u to s o m a l d o m in a n t M en d elian in h e rita n c e of a

facial fea tu re, th e p ro g n a th ic m an d ib le. The p ro g n a th ic m an d ib le w as

ob serv ed in 9 su ccessiv e g e n e ra tio n s of th e fam ily a n d a lth o u g h it

a p p e a re d to be tr a n s m itte d a s a n a u to s o m a l d o m in a n t tr a it th e m ale

m e m b e rs w ere d o c u m e n te d a s m ore severely affected.

In a d d itio n to th e genetic s tu d y of a c la ssic a l facial tr a it th e re

a re n u m e ro u s d o c u m e n te d in s ta n c e s of m o re in d iv id u a l facial tra its

in OMIM (M cK usick-N athans 2000). T his in c lu d e s lip p its, c h in

d im p les, e a r lobe a tta c h m e n t a n d h a ir line b u t in m o st c a se s

evidence is a n e c d o ta l a n d th e ju d g e m e n t a b o u t th e g en etic b a s is is