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LIVESTOCK GENETICS
AND BREEDING
DOMINANT AND RECESSIVE GENES
o CLF 254
Regan Steele - AgEd 410, Fall 2012
KEY TERMS
 Offspring
 Baby
 Dam
 Mother
 Sire
 Father
KEY TERMS
 Gene
 Genes are the items that determine your physical traits
 Genetics
 the science of heredity, dealing with resemblances and differences
of related organisms resulting from the interaction of their genes
and the environment.
 Genes have different forms which are known as ALLELES.
 There are 2 alleles on each chromosome
 For example, the gene for coat color could have two
alternatives - a white allele and a black allele.
Cattle Hair Color Black:
Bb
(BLACK)
( WHITE / RED)
 1.
Angus cattle coat color.

a. Black (B) is dominant.

b. Red (b) is recessive.
 2. Cross a homozygous black cow to a homozygous red bull.
 HOMOZYGOUS: having identical alleles for any one gene
BB x bb
Punnett
Square
B
b
B
Bb
b
The result is 4 calves that will be HETEROZYGOUS
black
HETEROZYGOUS
 Having 2 alleles, one that is dominant and one
that is recessive
B
b
DOMINANT GENE

1. A dominant gene covers (masks) the presence
of other genes.

2. Capital letters are used to designate
dominant genes.
B=
RECESSIVE GENE

1. A recessive gene is the one overridden by the dominant gene.
 2. Recessive genes are designated by small
letters.
 3. For a recessive trait to appear the animal
bb
must be homozygous (have two of the
same small letter chromosomes) for that
characteristic to appear.
PRACTICE QUESTION
In sheep black wool is recessive to white wool.
What happens when you mate a homozygous
black ram to a heterozygous white ewe?
bb + Bb
B
b
b
If video doesn’t work, right click here and open hyperlink
b
B
b
Bb
bb
(WHITE)
Bb
(BLACK)
bb
IMPORTANT DOMINANT & RECESSIVE
GENES IN LIVESTOCK
DOMINANT
RECESSIVE
 Polled Cattle
 Horned Cattle
 Black Cattle
 Red Cattle
 White Sheep
 Black Sheep
 White Pig
 Black Pig
 Normal Nose Horse
 Bleeding Nose Horse
WHY GENETIC SELECTION?
Bleeding Nose Horse
Cattle Horns
SUMMARY
 Genes are what determine our traits
 There are 2 ALLELES on each gene
 A lower case letter means that the trait is RECESSIVE
 A RECESSIVE gene is one that is over ridden by the
dominant gene
 In order to have red colored calf, we must have an
allele with 2 recessive genes
 An upper case letter means that the trait is
DOMINANT
 The DOMINANT gene masks the characteristics of
the recessive gene
 Two alleles of the same case are
HOMOZYGOUS
BB
 If one allele is upper case and one is lower case,
the gene is HETEROZYGOUS
 The PUNNETT SQUARE is an essential tool for
predicting characteristics of offspring
 GENETIC SELECTION allows for us to control
the undesirable and desirable traits in our
animals
bb
THE END!!