Question

1. There is a set of commercially available DNA markers, which were associated with increased meat quality in 2001. A recent study tested the meat quality of about 200 individuals tested for those markers and found no effect of the markers on the carcass quality of the animal s evaluated. How do you explain that?

Answer 1

Different Research studies have shown that effect of DNA markers on increased meat quality. Ex.

DNA markers of beef quality. With regard to beef meat quality, information on genetic markers is still very limited. Indeed,

genetic variability has been proved to be large enough for these traits and should enable genetic markers to be detected and then

used to increase beef quality through marker-assisted selection (MAS). During the past ten years, large efforts have been engaged

to detect QTLs, especially in the USA or in Canada and several studies on beef quality have also been performed in Australia,

Europe and Japan. These studies were recently reviewed (Kühn et al., 2005) and were mainly focused on tenderness and on the

amount and the composition of intramuscular fat. Several of them have investigated meat quality in B. taurus x B. indicus crosses,

where a very large difference in meat quality traits, particularly toughness, is known.

Tenderness. Several studies independently identified a QTL on BTA29 with effect on tenderness, either in crosses between B.

taurus and B. indicus or in crosses between B. taurus breeds (Casas et al., 2005 ; Schmutz et al., 2000 ; see review by Kühn et al.,

2005). Page et al. (2002) suggested that genetic variants of the CAPN1 (calpain 1) gene, which is located in the same

chromosomal region, are the functional background of this QTL, because 2 SNPs in exons 9 and 14 were associated with

variations in tenderness measured by a shear force test on Longissimus dorsi. It should be noted that these 2 polymorphisms

correspond to amino-acid substitutions (A316G and I530V) and that three combinations (alleles or haplotypes) have been

described. Other QTL with impact on beef tenderness traits were identified on BTA4, 5, 9, 11, 15, and 20, but have not been

confirmed in independent studies nor is there evidence for a gene within the QTL region that could be considered as a strong

candidate. On the contrary, polymorphisms in two genes, CAST (calpastatin) and LOX (Lysyl oxidase), both located on BTA7,

where no QTL for tenderness has been reported, have been associated with an effect on the beef tenderness trait (Barendse,

2002a). For CAST, 2 SNPs located in the 3’UTR region and a microsatellite located in the 5’ region were reported: only 2

haplotypes have been shown to be associated with improved tenderness and it was suggested that the known markers are in

linkage disequilibrium with a causative mutation that has not yet been identified.

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