Rainbow & Cc
Rainbow
& "
cc
", the world's
first cloned cat:
Genetics of tortoiseshell & calico cats
Shown here at 7
weeks,
cc
["
copy cat
": above, right]
was produced by nuclear transplantation of ovarian cumulus cells
from
Rainbow
, a
tri-colour calico
(orange / black / white) female
[above, left], into enucleated cat ova from an (unnamed) donor.
The surrogate mother,
Allie
, is a
bi-colour
tortoiseshell
(orange and black only) [below, with
cc
]. Analysis of seven polymorphic
microsatellite
loci
confirmed that
cc
is a genetic clone of
Rainbow
.
An interesting
aspect of this experiment is the marked difference between the
coat patterns of
Rainbow
and
cc
.
The
calico pattern
results from
an interaction between a
sex-linked colour locus
(
C
) and
an
autosomal white-spotting locus
(
W
). The
colour locus has two alleles,
O
and
B
, for
Orange
and
Black
. In heterozygotes,
X-chromosome inactivation
("
Lyonization
") early
in development results in melanocyte precursor cells that
express only one or the other allele: where an
X
bearing
the
O
allele is
inactivated, the melanocytes are black, and where
B
is
inactivated, the melanocytes are orange. Melanocytes migrate
into the epidermis, where they multiply and are seen as
differentially-coloured fur patches. The effect of the autosomal
White
locus is to slow
migration of melanocytes: white fur patches result when
melanocytes fail to reach the epidermis. The slower the
migration, the more extensive the white patches, and the less
time there is for the colored patches intermingle. Thus,
t
r
i
-colour
calicos
show more discrete colour patches the more
white they have, and
b
i
-colour
tortoiseshells
show a brindled pattern, with orange and
black fur more intimately mixed.
Why doesn't
Rainbow
look
exactly
like her clone,
cc
? Note first that the proportion and
pattern of white fur are roughly the same. Thereafter, the
pattern of
X
-chromosome
inactivation in different cells is essentially random, and the
movements of melanocytes to the skin cells are also random.
Thus, even though
Rainbow
and
cc
have identical
tortoiseshell
genotypes
, the
phenotypes
of
their coat patterns are quite different, and their clonal
identity is only apparent from genetic tests.