Transcript Document
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!!