Mendelian Inheritance in Goats

There are several genetic disorders associated with characteristics found in goats, which are caused by single genes. These are summarized in Tables 1 and 2. The autosomal dominant polled gene P, causes hornlessness and its recessive (p) causes sexual abnormality in goats.[1'2] The absence of wattles and the absence of ears have been shown to be recessive characters.1-2-1 Coat color may be important in skin and hair production (e.g., in the Red Sokoto and Cashmere goats). The order of dominance in coat color is white, red, fawn or chamois, and black, and the wild-type face pattern found in Toggenburgs is dominant to the reversed pattern known as badger face.[3]

Traditionally, genetic crosses have been used to determine the presence of alleles that code for a particular phenotype. In qualitative inheritance, only one pair of genes or a single locus is involved. Most inheritance involves multiple genes or quantitative trait loci (QTL).[4] Recent advances in molecular genetic analyses restriction fragment length polymorphism analyses (RFLP), randomly amplified polymorphic DNA (RAPD), simple sequence repeat (SSR) microsatellites, amplification fragment length polymorphism (AFLP), and single nucleotide polymorphism (SNP) analyses have allowed the development of a variety of DNA-based markers. With sufficiently dense genetic maps, entire genomes can be scanned for genes associated with QTL.[5] Once a QTL has been identified, populations can be tested quickly and easily for the frequency of alleles and associated phenotypes.

The Tennessee Stiff-legged or the Myotonic goat has a condition called myotonia congenita. By the sequencing of the genes of affected and nonaffected goats, a single nucleotide polymorphism that caused an amino acid change in the CIC-1 protein was found.[6] This change reduced the effectiveness of the channel to remove chloride ions. Through molecular genotyping for the CIC-1 gene, Sayre et al.[7] have identified a positive association with the single nucleotide polymorphism and the myotonia phenotype. The identification of this genotype/phenotype relationship allows for an easy test for the presence of myotonia in goats and may allow for more extensive analyses of the effects of myotonia on carcass and performance traits.

Table 1 Cause and effect of qualitative characters in goats

Dominant Recessive phenotypes phenotype Effect

Dominant Recessive phenotypes phenotype Effect

Table 1 Cause and effect of qualitative characters in goats

PP

Pp

pp

Polledness, due to dominant autosomal gene P.

The P gene has a recessive masculinizing effect with complete penetrance in females and incomplete penetrance in males.[1'2]

WW

Ww

ww

Presence of wattles. Does with wattles were 13% more prolific than ww does.[2] Note: polled females with wattles (PPPp+WWWw) were 25.6% more prolific than the average.[2] Absence of wattles.

EE

Ee

ee

Presence of long or normal ears.

Absence of ears, or ''gopher ears.'' The American La Mancha breed.[2]

CC

Cc

Roan, red, or chamoisee coat color (Saanen).

Black or dark coat color.

Sayre et al.[7] discussed in detail genotyping methodologies and strategies, marker analyses, and lactation-related genes in goats. Using various sequencing methods and protein analyses, alleles in caseins and beta-lactoglobulins have been identified. Once the different alleles were identified, PCR-RFLP procedures were used to determine differences in phenotype associated with the presence of the various alleles. Differences in goat milk casein have been implicated as a possible explanation for an apparent lower allergic response to goat milk consumption compared to cow milk. A discussion on scrapie resistivity/susceptibility and identification using genotyp-ing protocol is also provided.[7]

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