longer story in Agricultural Research.
Building a Genetic Road Map to
By Jan Suszkiw,
July 6, 2000
Like road crews installing signposts
along a highway, Agricultural Research
Service scientists are marking off regions of cow DNA harboring a plethora
of traits--from mastitis resistance, to milk proteins for enriched dairy
Melissa Ashwell's team at ARS'
Gene Evaluation and Mapping
Research Laboratory in Beltsville, Md., is among other groups now seeking
to map the genome of dairy and beef cattle. One spinoff of the Beltsville work
could be genetic tests that employ DNA markers to predict the degree to which
newborn calves will express traits inherited from a prized bull sire.
The markers are short stretches of chemicals called nucleotides comprising
cow DNA, found tightly coiled inside 29 chromosomes. At Beltsville, Ashwell's
team is using a technique called quantitative trait loci or QTL detection to
identify DNA regions harboring desirable genes--such as for certain milk
proteins that improve cheese.
Since the mid-1990s, Ashwells team has examined nearly 200 different
markers. Genetic tests employing these markers are still a few years off,
according to Ashwell. But developed commercially, the technique could save
dairy breeders considerable time and money spent rearing calves sired by a
prized bull. Currently, it takes five years before a calf's traits can be fully
evaluated. With marker assisted selection, such evaluations could begin with a
few embryonic cell samples, or using blood drawn from a newborn calf.
On chromosome 27, scientists already have developed markers for genes
associated with "dairy form." This describes a cow's physical
appearance, and may also be an indicator of animals prone to ketosis, a
metabolic disorder typically affecting cows with newborn calves.
A longer story about the team's work appears in the July issue of Agricultural
Research magazine on the Web at:
ARS is the U.S. Department of
Agriculture's chief scientific agency.
Scientific contact: Melissa Ashwell, ARS Gene Evaluation and Mapping
Research Laboratory, Beltsville, Md., phone (301) 504-8543, fax (301) 504-8414,