GENETIC POLYMORPHISMS AT THE K-CASEIN LOCUS IN PANTANEIRO CATTLE(POLIMORFISMOS GENÉTICOS EN EL LOCUS DE LA K-CASEÍNA EN GANADO BOVINO DE RAZA PANTANEIRA)

Lara M.A.C.

Description

Abstract
First results on genetic variability at the kcasein locus are reported for the Pantaneiro breed of cattle, based on DNA analysis by PCR-RFLP of blood samples from 117 animals. Estimated gene frequencies were 0.7820 ± 0.0281 and 0.2180 ± 0.0281 for the A and B alleles, respectively, with an observed heterozygosity of 0.368. Based on information at this locus, no evidence was found of disequilibrium in the population. Comparison with allele frequencies in other cattle breeds indicates that frequencies in Pantaneiro are intermediate between those observed in Bos taurus and Bos indicus breeds.
Resumen
En este estudio se presentan los primeros resultados sobre la variabilidad genética en el locus de la k-caseina en ganado de raza Pantaneira. Se analizaron 117 muestras de ADN mediante las técnicas de PCR-RFLP. Las frecuencias obtenidas para los alelos A y B fueron 0,7820 ± 0,0281 y 0,2180 ± 0,0281, respectivamente, y la heterocigosidad observada fue de 0,368. Con base en la información sobre este locus, no se encontró evidencia de que la población no estuviera en equilibrio. Las frecuencias alélicas que fueron estimadas en Pantaneiro son intermedias entre aquellas obtenidas en razas de origen Bos taurus por un lado y Bos indicus por el otro .

Sujets

• Genetic variability
• Zygosity
• Variabilidad genética

Informations

• Publié par: erevistas
• Publié le: 01 janvier 2002
• Nombre de lectures: 21

Extrait

GENETIC POLYMORPHISMS AT THE K CASEIN LOCUS IN
PANTANEIRO CATTLE
POLIMORFISMOS GENÉTICOS EN EL LOCUS DE LA K CASEÍNA EN
GANADO BOVINO DE RAZA PANTANEIRA
1 2 1 3 1Lara, M.A.C., L.T. Gama, G. Bufarah, J.R.B. Sereno, E.M.L. Celegato and
3U.P. de Abreu
1Instituto de Zootecnia. C. Postal 60. 13460 000 Nova Odessa, SP. Brazil. E mail: [e-mail]
2Estação Zootécnica Nacional. Fonte Boa. 2000 Santarém. Portugal.
3Embrapa Pantanal. C. Postal 109. 79320 900, Corumbá, MS. Brazil.
ADDITIONAL KEYWORDS PALABRAS CLAVE ADICIONALES
Genetic variability. Heterozygosity. Genetic Variabilidad genética. Heterocigosidad. Recur
resources. sos genéticos.
SUMMARY
First results on genetic variability at the k- 0,7820 ± 0,0281 y 0,2180 ± 0,0281, respectiva
casein locus are reported for the Pantaneiro breed mente, y la heterocigosidad observada fue de
of cattle, based on DNA analysis by PCR RFLP of0,368. Con base en la información sobre este
blood samples from 117 animals. Estimated gene locus, no se encontró evidencia de que la pobla
frequencies were 0.7820 ± 0.0281 and 0.2180 ± ción no estuviera en equilibrio. Las frecuencias
0.0281 for the A and B alleles, respectively, with alélicas que fueron estimadas en Pantaneiro son
an observed heterozygosity of 0.368. Based on intermedias entre aquellas obtenidas en razas
information at this locus, no evidence was found de origen Bos taurus por un lado y Bos indicus por
of disequilibrium in the population. Comparison el otro.
with allele frequencies in other cattle breeds
indicates that frequencies in Pantaneiro are
intermediate between those observed in Bos INTRODUCTION
taurus and Bos indicus breeds.
Selection of dairy sires and cows
has been based mostly on quantitative
RESUMEN traits such as milk, fat or protein yield,
which are assumed to be controlled by
En este estudio se presentan los primeros multiple loci. Genetic improvement of
resultados sobre la variabilidad genética en el quantitative traits is, therefore,
locus de la k caseina en ganado de raza relatively slow, as productive traits
Pantaneira. Se analizaron 117 muestras de ADN can only be measured in one sex, are
mediante las técnicas de PCR RFLP. Las fre affected by numerous polygenes (each
cuencias obtenidas para los alelos A y B fueron polygene exerting a small effect on the
Arch. Zootec. 51: 99 105. 2002.LARA, GAMA, BUFARAH, SERENO, CELEGATO AND ABREU
trait) and environmental factors have particularly certain k Cn and b Lg
an important influence on their variants, are associated with lactation
expression. This undoubtedly lowers performance and have a major influ
the accuracy of genetic evaluation of ence on milk composition and its
sires and cows. In addition, productive processing properties, including cheese
traits can only be measured in adult yield (Marziali and Ng Kwai Hang,
animals, thereby increasing the 1986; Grosclaude, 1988, Aleandri et
generation interval and lowering the al., 1990).
genetic progress per year. Relationships between genotypes
For this reason, qualitative charac for different milk proteins and yield
ters, such as polymorphisms in blood traits have been reported by several
groups, enzymes, blood serum proteins authors (Lin et al. , 1992). For example,
or milk protein types, are among thoseassociations between milk protein
being investigated for the possibilities genotypes and milk production from
which they provide of improving the 6803 first lactation records were
accuracy of estimating genetic merit estimated by Bovenhuis et al. (1992).
of sires and cows and practicing In this study, k casein genotype had a
selection at an earlier age (Lin et al., significant effect on milk production
1992). More recently, genome scanning (p<0.001), with cows of the BB
based on microsatellite loci has also genotype producing 173 kg less milk
been used to detect the possible locationthan AA cows. Furthermore, k casein
of genes with a major effect on genotypes had a highly significant
productive traits (Boichard, 1998; effect on protein content (p<0.001),
Gomez Raya et al., 1998). such that k casein BB cows produced
Milk protein polymorphisms have milk with a 0.08 percent higher protein
received considerable research interest content than that of AA cows. The
because of their potential use as an aid same authors found that, for fat content,
to genetic selection and to genetic the effect of k casein genotype was
characterization of bovine breeds (Del not significant, while for fat yield the
Lama and Zago, 1996; Golijow et al,. B allele was associated with a signifi
1996 and 1999; Tambasco, 1998; cantly lower production of fat when
Kemenes et al., 1999). compared with the A allele.
Specific proteins in bovine milk Genotyping of milk proteins, such
include four caseins ( as1, as2, b and as k casein, can be performed by
k casein), and two whey proteins ( a- electrophoresis, directly from milk
lactalbumin: a La, and b lacto samples, as the expression of caseins
globulin: b Lg), each protein showing occurs only during the lactation phase
at least two genetic variants (Eigel et in mammary gland cells. Therefore,
al., 1984). The k casein variants A e B the use of electrophoresis for genoty
differ by two amino acid substitutions, ping of milk proteins is strongly limited
i.e., Thr136/Ile and Asp148/Ala (Lin because it can only be used in cows in
et al., 1992) the lactation stage. With newly
Several studies have reported that developed techniques based on DNA
some of these bovine protein variants, analysis, which include polymerase
Archivos de zootecnia vol. 51, núm. 193 194, p. 100.THE K CASEIN LOCUS IN PANTANEIRO CATTLE
chain reaction and restriction fragment for Pantaneiro cattle of EMBRAPA
length polymorphisms (PCR RFLP) Pantanal. DNA was obtained by
methods (Medrano and Aguilar digestion with proteinase K and salt
Cordova, 1990; Denicourt et al., 1990), extraction (Olerup and Zetterquist,
it is now possible to determine the k 1992) and DNA samples were typed
casein genotype of all individuals in a using the PCR RFLP method.
given population under selection, To analyze the k casein (k CN)
regardless of sex, age or physiological locus, a 350 bp fragment covering the
stage. As a result, it is now possible to sequence containing the mutation site
include information on milk protein was amplified according to the
genotypes into selection programs, procedure proposed by Medrano and
which should result in more accurate Aguilar Cordova (1990). The amplicon
predictions of breeding values of was digested with HinfI restriction
0animals to be selected, and thus endonuclease at 37C for three hours,
improve response to selection. to distinguish between A and B alleles.
Genetic variability in the k casein For each reaction, 10 ml of PCR product
locus has been reported for several and 3.75 units of HinfI were used in 50
breeds, with allelic frequencies mM Tris HCl buffer, pH 8,0, contai
incorporated into studies on genetic ning 10 mM MgCl and 50 mM NaCl.
2
diversity among breeds (Golijow et The restriction fragments were se
al., 1996; Del lama e Zago, 1996; pareted in vertical polyacrylamide gel
Kemenes et al., 1999). 10 percent and silver stained at 3
The Pantaneiro breed of cattle percent.
represents an excellent source of Allele frequencies were determined
biological information for studies on by gene counting. A Chi square test
genetic characterization, as it results was carried out to evaluate if the
from a long process of natural selection.population was in Hardy Weinberg
This breed has been kept basically equilibrium.
with no selection for productive traits,
and it should therefore maintain the
RESULTS AND DISCUSSIONgenetic variability which has allowed
it to adapt and survive in the adverse
Identification of A and B alleles ofconditions of the Pantanal region.
k casein was performed by ampli The objective of this work was to
fication of a DNA fragment of 350 bp,study gene frequencies at the k casein
located between exon IV and intronlocus in Pantaneiro cattle, and compa
IV, by the PCR RFLP method. There them with those reported for different
DNA fragment amplified from allele Bcommercial cattle breeds.
shows only one restriction site,
resulting in two fragments of 266 and
84 bp. Allele A was characterized byMATERIALS E METHODS
the presence of three fragments,
Peripheral blood was sampled from corresponding to 134, 132 and 84 bp.
117 cattle of the Conservation NucleusThe patterns of the three possible k-
Archivos de zootecnia vol. 51, núm. 193 194, p. 101.LARA, GAMA, BUFARAH, SERENO, CELEGATO AND ABREU
casein genotypes are shown in figure 1 .
bp
Genotypic frequencies were 0.598,
350
0.368 and 0.034 for AA, AB and BB, ? 266
respectively. Frequencies of alleles A
and B, estimated from genotypic
? 134 / 132
frequencies, were 0.7820 ± 0.0281 and
840.2180 ± 0.0281, respectively (table
I). Genetic variation at the k casein
locus has not been previously reported
1 2 3 4 5 6
for Pantaneiro cattle, but the observed
heterozygosity indicates a high genetic
Figure 1. Patterns of restriction fragmentsvariabilility in this population, in
of k casein after digesti