Íslenskar landbúnaðarrannsóknir - 01.03.1970, Page 53

COLOUR INHERITANCE IN ICELANDIC SHEEP 51
TABLE 12
Progeny of ram No. 06043, according to genotype of dams.
For explanations see text
Ewe group Genotype Colour group o£ progeny Total
1 2 3
1 Ai—, A1A4 4 0 0 4
9 AiAj, i 4 4 4 5 13
3 A4A5 2 10 5 17
4 AiAj’ i« j =£ 1 or 4 6 21 36 63
Total 16 35 46 97
cause dominant white would be assumed
to occur equally frequently with A4 and
A5 alleles. The possibility of a new type
of dominant white, non-allelic to A4 and
A5 has therefore also to be rejected.
If mosaicism is assumed as an explana-
tion, the ram could originally liave been
of any of the 3 genotypes, A4A4, A^A^ or
A4A5. Below are set out the 6 possible
mutations among these 3 genotypes which
would lead to the three alleles observed
being present in his gonads, together with
the expected ratios among the gametes.
Genotype Situation Mutation Expected relative frequency of allele
Ai a4 a5
A1A4 1 Ai Ag 0.5 - p 0.5 P
2 a4 -» a5 0.5 0.5 — p P
A1A5 3 Ai -» A4 0.5-p P 0.5
4 a5 -» a4 0.5 P 0.5-p
A4A5 5 A4 -» Ai P 0.5-p 0.5
6 A5 Ai P 0.5 0.5 -p
In the above, p is the proportion of
gametes which carry the new allele.
The new allele will never be more fre-
quent than the original allele from which
the mutation arose, and in terms of allele
frequencies this leads to the condition that
p ^ 0.25.
In order to test wliich of the 6 situa-
tions has the highest probability, the ob-
served frequencies of the mutated allele
and its allele of origin should be added, and
this sum is expected to equal the frequ-
ency of the unaffected allele.
The colours to be grouped together in
each of the 6 situations are shown in table
13.