Page 10 - Ranui Catalogue 2021 ebook

RECESSIVE

GENETIC CONDITIONS
recessive genetic conditions
This is information for bull buyers about the recessive genetic conditions, Arthrogryposis Multiplex (AM),
Hydrocephalus (NH), Contractural Arachnodactyly (CA) and Developmental Duplications (DD).
Putting undesirable Genetic Recessive Conditions in If animals tested free of the undesirable gene are
perspective mated to carrier animals the condition will not be
expressed at all. All calves will appear normal, but
All animals, including humans, carry single copies approximately half (50%) could be expected to be
(alleles) of undesirable or “broken” genes. In single carriers.
copy form, these undesirable alleles usually cause no
harm to the individual. How is the genetic status of animals reported?
But when animals carry 2 copies of certain DNA-based diagnostic tests have been developed
undesirable or “broken” alleles it often results in which can be used to determine whether an
bad consequences. Advances in genomics have individual animal is either a carrier or free of the
facilitated the development of accurate diagnostic alleles resulting in AM, NH, CA or DD.
tests to enable the identification and management Angus Australia uses advanced software to calculate
of numerous undesirable or “broken” genes. the probability of (untested) animals to being
Angus Australia is proactive in providing its members carriers of AM, NH, CA or DD. The software uses the
and their clients with relevant tools and information test results of any relatives in the calculations and
to assist them in the management of known the probabilities may change as new results for
undesirable genes and our members are leading the additional animals become available.
industry in their use of this technology. The genetic status of animals is being reported using
What are AM, NH, CA and DD? five categories:
AM, NH, CA and DD are all recessive conditions caused AMF Tested AM free
by “broken” alleles within the DNA of individual Based on Pedigree AM free - Animal
animals. When a calf inherits 2 copies of the AM or AMFU has not been tested
NH alleles their development is so adversely affected
that they will be still-born. AM_% _% probability the animal is an AM
In other cases, such as CA and DD, calves carrying carrier
2 copies of the broken allele may reach full-term. In AMC Tested AM-Carrier
such cases the animal may either appear relatively AMA AM-Affected
normal, or show physical symptoms that affect their
health and/or performance. For NH, CA and DD, simply replace AM in the above
table with NH, CA or DD.
How are the conditions inherited? Registration certificates and the Angus Australia
Research in the U.S. and Australia indicates that web-database display these codes. This information
AM, NH, CA and DD are simply inherited recessive is displayed on the animal details page and can be
conditions. This means that a single gene (or pair of accessed by conducting an “Database Search” from
alleles) controls the condition. the Angus Australia website or looking up individual
For this mode of inheritance two copies of the animals listed in a sale catalogue.
undesirable allele need to be present before the Implications for Commercial Producers
condition is seen; in which case you may get an
abnormal calf. A more common example of a trait Your decision on the importance of the genetic
with a simple recessive pattern of inheritance is black condition status of replacement bulls should depend
and red coat colour. on the genetics of your cow herd (which bulls you
Animals with only one copy of the undesirable allele previously used) and whether some female progeny
(and one copy of the normal form of the allele) will be retained or sold as breeders.
appear normal and are known as “carriers”. Most Angus breeders are proactive and transparent
in managing known genetic conditions, endeavouring
What happens when carriers are mated to other to provide the best information available. The
animals? greatest risk to the commercial sector from
Carriers, will on average, pass the undesirable allele undesirable genetic recessive conditions comes from
unregistered bulls with unknown genetic background.
to a random half (50 %) of their progeny. The genetic condition testing that Angus Australia
When a carrier bull and carrier cow is mated, there seedstock producers are investing in provides buyers
is a 25% chance that the resultant calf will inherit of registered Angus bulls with unmatched quality
two normal alleles, a 50% chance that the mating assurance.
will result in a carrier (i.e. with just 1 copy of the For further information contact Angus Australia’s
undesirable allele, and a 25% chance that the calf Breed Development & Extension Manager on
will inherit two copies of the undesirable gene.
(02) 6773 4618.
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