Page 103 - NZ Herefords Magazine 2018

Industry Focus

DNA technologies for beef cattle

THERE IS NOW A RANGE OF DNA-BASED TECHNOLOGIES AVAILABLE
THAT CAN BE APPLIED WITHIN A BEEF ENTERPRISE. BEFORE MAKING
THE DECISION TO INVEST IN DNA TECHNOLOGIES, IT MAKES SENSE
TO BE INFORMED ABOUT THE THEORY OF DNA AND THE CURRENT
APPLICATIONS AVAILABLE.

WORDS NZHA / SOUTHERN & TROPICAL BEEF TECHNOLOGY SERVICES
PHOTOGRAPHS SUPPLIED

THE THEORY OF DNA

WHAT IS DNA?
Deoxyribonucleic acid (DNA) is a molecule found in all bovine
cells. It is often described as the ‘blueprint’ of an organism
because it codes the instructions for how that organism will
develop, function and appear.
For storage, DNA is bundled into chromosomes, of which
cattle have 30 pairs. Within the chromosomes, there are
approximately three billion base pairs of bovine DNA. The
base pairs are made up of four types; Adenine (A), Thiamine
(T), Guanine (G) and Cytosine (C). The sequences of these SNP occurence in a single
base pairs make up the ‘message’ of DNA, and differences in base pair.
sequences provide the basis for variation between individuals. SNPs are replacing microsatellites as the genetic marker of
choice because of their greater abundance and stability. The
greater abundance of markers means more markers can be
included in any test, allowing them to be more powerful and
accurate, and the greater stability means the test will remain
accurate over many generations. DNA laboratories are also
phasing out microsatellite testing due to difficulties in obtaining
replacement equipment and reagents to perform the tests.

Animal Within Chromosomes CURRENT APPLICATIONS OF
made of each cell are made of
cells. nucelus are DNA. DNA TECHNOLOGY
chromosomes
There are many potential applications of DNA technology
WHAT IS A GENE? within a beef seedstock enterprise. Some of the most common
A gene is a sequence of base pairs at a particular location on the current applications include:
chromosome, which codes for a specific product. It is estimated i. Parentage verification – DNA parentage verification works
that there are between 22,000 and 28,000 genes in the beef by analysing a series of DNA markers in the progeny and
animals. For each gene there may be two or more variants, known in potential parents. For each DNA marker, one of the two
as alleles, which can result in different phenotypes or observable variants observed in progeny must have come from the
characteristics. Each individual has two alleles for each gene, one dam and the other from the sire. Therefore, potential parent
copy inherited from their father and one copy from their mother. combinations can be ruled out as the parents if their DNA
markers do not match those observed in the progeny. While
WHAT IS A GENE MARKER (OR DNA MARKER)? both microsatellite and SNP markers have been used in
The two types of DNA markers commonly used in beef parent verification, SNPs are becoming the marker of choice
cattle are microsatellites and single nucleotide polymorphisms due to their greater abundance/accuracy and stability.
(SNPs). A microsatellite is a repeat of a particular base pair ii. Management of genetic conditions – genetic conditions
sequence at a specific location in an animal’s DNA. The number or defects are caused by DNA abnormalities and are
of base pair repeats can differ between animals. present in all species, including beef cattle. The incidence
SNPs occur where there is a difference in a single base pair, of genetic conditions is normally low within a population,
as highlighted in Fig 2, where the top animal has a C and G though more inbreeding or the rapid dissemination of
base pair at a particular location whereas the bottom animal has genes through artificial breeding can lead to an escalation
a T and A base pair. in the prevalence of a genetic condition. Over 400 genetic
101