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When the highly successful American racehorse,
Cigar, was put to stud, he proved to be infertile.
There was talk of cloning Cigar. However, if the
original Cigar is infertile because of a genetic
defect, his clone will also be infertile. If the
original Cigar is infertile because of an illness
or injury, the clone should be fertile.
A clone will be the same gender as the tissue
donor. At present there is no way to change a
clone's gender. The chromosomes which determine
gender are the sex chromosomes. Females have 2 'X'
chromosomes (XX) and males have one X and one Y (XY).
A few individuals have multiple sex chromosomes or
only one sex chromosome, but these are out of the
scope of this article.
Scientists have considered creating female
clones from male cells by removing the Y
chromosome and somehow duplicating the X
chromosome. This is fine in theory but may not
work in practice because some genes on the sex
chromosomes HAVE to be inherited from the father
if the offspring is to be normal. These issues are
complex and are discussed in detail in Matt
Ridley's "Genome".
In humans there are all sorts of conditions
which arise if genes are inherited from 'the wrong
parent' . This occasionally happens in nature if 2
ova (egg cells, these always contain an X
chromosome) fuse to create an XX embryo without
any genes from a male parent. Also, there isn't
yet a way of turning an X chromosome into a Y
chromosome to get a male clone from a female
tissue donor.
Limitations
of Cloning 2: Color & Pattern
There's bad news for owners of tortie and
calico cats. DNA tests have confirmed that CC is a clone of
her genetic mother. Yet her coat color and pattern
is different from that of her mother because the
pattern of pigmentation in multicolored animals is
the result of genetic factors combined with
developmental factors within the womb. This means
bad news for owners who want an exact replica of a
tortoiseshell or calico cat.
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