8/14/2019 Sheep Management 4

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8/14/2019 Sheep Management 4

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ISSN 0726-934X

State of Western Australia, 2005

Sets of pairs of genes, not single genepairs, mediate all production traits insheep. Hundreds or thousands of genesmay be implicated. A set of genes thataffects the genetic expression of a trait iscalled a genotype. Table 1 shows thenumber of different genotypes that arepossible with different numbers of gene

pairs.

With as few as 20 genes, the number ofgenotypes appears to become infinite. Although this number of differentgenotypes can lead to genetic variationbetween sheep, the differences caused bydifferent genes are indistinguishablebecause:

such small differences are notmeasurable; and

environmental effects substantiallyaffect multiple gene traits, obscuring

small genetic differences.

Further reading

Farmnote No. 52 /93 Sheep breeding: Heritability(Agdex 430/30).

Farmnote No. 73/2003 Genetic nomenclature andanimal breeding terms (Agdex 400/30).

Editorial assistance: Eliza Compton, Information andMedia Services.

Table 1. Number of genotypes possible with

increasing numbers of gene pairs

Number of gene pairs Number of genotypes

1 3

2 3

3 27

20 3.487 billion

n 3n

Figure 2. Male and female hogget liveweights plotted separately to show thedifference in mean and standard deviation.