The results of the huacaya×suri matings are troublesome
under the hypothesis of a single dominant gene. Even
under the most favorable assumption of all suri parents
being heterozygous there is an excess of huacaya offspring.
Under the assumption of any homozygous animals within
the suri population, that excess only becomes greater and
therefore less likely to fit with the single dominant gene
hypothesis.
Previously published data also reveal inconsistencies
with a single-gene hypothesis. The data of Renieri et al.
(2009) included the production records of 19 suri males
which each produced between 3 and 34 offspring following
mating to suri females (total of 362 offspring).
Each of those males had produced at least 1 huacaya
offspring from suri mates. The data of Ponzoni et al.
(2003) included offspring of 11 suri males, 9 of which
had produced huacaya offspring, and the remaining two
had produced only 1 and 3 offspring each (all offspring
of these two were suri). Bustinza Choque (2001) summarized
a study in 1971 in which huacaya×huacaya matings
produced 15 suris among 738 total offspring (2%), and
suri×suri matings produced 89 huacayas among 511 total
offspring (17.4%). Bustinza Choque then cites later data (of
unspecified year) of 15,000 births. In these data suri×suri
matings produced 1.2% huacaya, and huacaya×huacaya
matings produced 0.1% suri offspring, and that further
selection has reduced the production of offtype offspring
to 0.03%.
When taken together, these data are consistent with
a relatively simple genetic difference between these two
fleece types, although with some important reservations.
Suri is clearly “generally dominant” but more complicated
in some situations than a single dominant gene. Two phenomena
point to suppression of suri phenotype in some
instances. One is the excess of huacaya offspring in the
huacaya×suri matings. This result indicates that some
huacayas have the potential to mask the usually dominant
suri allele. A second is the consistent trend that all or most
suris with sufficient offspring numbers have produced huacaya
offspring at least rarely. The huacaya offspring of
suri×suri matings are likely of two different genetic types.
One is the expected huacaya that segregates from heterozygous
suri parents. The second is more likely to have
suppression of the suri phenotype, which is implied by production
of these in very low numbers by animals that are
otherwise identified as likely to be homozygous by large
numbers of suri offspring. This situation is consistent with a
genetic mechanism for suppression of suri phenotype, and
is more likely if the suppressor is recessive. The production
of an excess of huacaya offspring from suri×huacaya matings
could be consistent with either dominant or recessive
suppression, as gene frequencies could be set to support
either hypothesis. It is also possible that multiple independent
suppressor mechanisms exist, each with its own
pattern of inheritance.
The results of the huacaya×suri matings are troublesome
under the hypothesis of a single dominant gene. Even
under the most favorable assumption of all suri parents
being heterozygous there is an excess of huacaya offspring.
Under the assumption of any homozygous animals within
the suri population, that excess only becomes greater and
therefore less likely to fit with the single dominant gene
hypothesis.
Previously published data also reveal inconsistencies
with a single-gene hypothesis. The data of Renieri et al.
(2009) included the production records of 19 suri males
which each produced between 3 and 34 offspring following
mating to suri females (total of 362 offspring).
Each of those males had produced at least 1 huacaya
offspring from suri mates. The data of Ponzoni et al.
(2003) included offspring of 11 suri males, 9 of which
had produced huacaya offspring, and the remaining two
had produced only 1 and 3 offspring each (all offspring
of these two were suri). Bustinza Choque (2001) summarized
a study in 1971 in which huacaya×huacaya matings
produced 15 suris among 738 total offspring (2%), and
suri×suri matings produced 89 huacayas among 511 total
offspring (17.4%). Bustinza Choque then cites later data (of
unspecified year) of 15,000 births. In these data suri×suri
matings produced 1.2% huacaya, and huacaya×huacaya
matings produced 0.1% suri offspring, and that further
selection has reduced the production of offtype offspring
to 0.03%.
When taken together, these data are consistent with
a relatively simple genetic difference between these two
fleece types, although with some important reservations.
Suri is clearly “generally dominant” but more complicated
in some situations than a single dominant gene. Two phenomena
point to suppression of suri phenotype in some
instances. One is the excess of huacaya offspring in the
huacaya×suri matings. This result indicates that some
huacayas have the potential to mask the usually dominant
suri allele. A second is the consistent trend that all or most
suris with sufficient offspring numbers have produced huacaya
offspring at least rarely. The huacaya offspring of
suri×suri matings are likely of two different genetic types.
One is the expected huacaya that segregates from heterozygous
suri parents. The second is more likely to have
suppression of the suri phenotype, which is implied by production
of these in very low numbers by animals that are
otherwise identified as likely to be homozygous by large
numbers of suri offspring. This situation is consistent with a
genetic mechanism for suppression of suri phenotype, and
is more likely if the suppressor is recessive. The production
of an excess of huacaya offspring from suri×huacaya matings
could be consistent with either dominant or recessive
suppression, as gene frequencies could be set to support
either hypothesis. It is also possible that multiple independent
suppressor mechanisms exist, each with its own
pattern of inheritance.
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