Sheep - AgRIS

are capable of producing two kinds of lambs with respect to their color appearance. They may
be white or black. But there will be three kinds of lambs with respect to their genetic make-up.
White is dominant over black, and there may be lambs that are pure or homozygous for white,
heterozygous for white and black, and others that are pure for black. Since black is a recessive
color in most of our common sheep, only lambs that are pure for black have a black color.
Therefore, if a black lamb is horn it gets that character equally from both parents.
The same processes are involved with respect to all characters that are due to single genes.
If a ram was homozygous for all characters he possessed, his offspring from ewes that had
dissimilar characters could not possibly be homozygous. Thus, the only way to maintain a
homozygous condition once it has been developed is to restrict mating to individuals that are
homozygous. Mating brother and sister does not in itself insure progeny that is homozygous.
Even with a homozygous condition with respect to the genes, it would be improper to
expect all progeny to be exactly alike, for some characters that are to be found in individuals
are due to physiological reactions, which of course may in turn be related to the genes which
have been transmitted from the parents. Horns are undoubtedly an inherited character, but
certain physiological processes or substances must be present for the inheritance to become
evident. It is possible that physiological processes are influenced by the interaction of various
genes.
Some characters are due to single genes, but not all the characters. Some are due to two or
more genes where the degree of interaction may vary. Dominance may not always be complete,
and partial dominance introduces more complexity. Likewise, there are cases when a character
may be dominant in one sex but not in the other.
5.2 Blood Groups
Systematic studies on blood groups of Indian sheep were conducted by Raina (1969). All
antibodies were observed in normal sera of group O sheep and were used as reagents for
detecting R blood-group factor on sheep erythrocytes. The anti-O antibodies were found in
normal sera of two out of 89 sheep tested and were used as reagents. The highest titres of anti-R
and anti-O were found around September and lowest around March-May. The erythrocytes of
new-born lambs lacked the R and O subKstances, though these antigens were present in the
respective blood sera.
Twenty-seven blood-group factors belonged to nine different blood-group systems, of
which A,B,C, M and R-O systems were previously described, and F,G,H and K systems were
the new bloodgroups systems not reported earlier. Fourteen blood-group factors were
recognized in the B-system, where 51 alleles were recognized. Twelve C pheno-groups
controlled by 12 different alleles were recognized in the C system. A system was observed to
have two alleles giving two distinct phenotypes. The l\iystem also had 2 alleles giving Z
distinct phenotypes.
5.3 Biochemical Polymorphism
5. 3.1 Haemoglobin
Indian sheep show normally three distinct haemoglobin (Hb) phenotypes, viz. AA, BB and
AB resulting from two alleles A and B (Agar 1969,Agar and Evans 1969 a,b, Agar et al. 1969,
Kalla et al. 1970, Arora 1970, Arora et al. 1970 a, Agar and Seth 1971, Singh et al. 1972 a,b,
Singh et al. 1976 a, b, Arora and Arora 1978, Kandesamy 1979 and Arora 1979). Another type
i.e. Hb C has also been reported in a highly anaemic Nali lamb (Arora et al. 1970 b).
The gene frequencies of haemoglobin types in various breeds in India are given in Table
20.1. In Indian breeds, individuals with Hb B predominated. Indian meat types breeds (Nellore
and Mandya) and their crosses with Indian carpet wool breeds and exotic mutton breeds
(Suffolk and Dorset) and their crosses with Malpura and Sonadi show a higher frequency of
Hb B type. In some breeds of hilly region the frequency of Hb A is found more.
Haemoglobin types are inherited in simple Mendelian fashion. The two haemoglobin
types, viz. Hb A and Hb B are controlled by two alleles codominant to each other, each
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