1. Genetics and Breeding

2. Interest Approach Ask students why they don’t look like each other (if they had the same parents)

3. Terms Allele A pair of genes which are located at the same place on homologous chromosomes (the matched pair). Often applied to the traits associated with the genes.

4. Terms cont. Phenotype The physical appearance of the animal because of its genetic makeup

5. Terms cont. Genotype Genetic constitution (makeup) of an individual

6. Terms cont. Gene A specific region of a chromosome which is capable of determining the development of a specific trait that is composed partially or wholly of DNA

7. Terms cont. Dominant Refers to genes which hide or mask the presence of other genes

8. Terms cont. Recessive Gene whose phenotypic expression is masked when in the presence of a dominant allele

9. Terms cont. Heterozygous An animal that carries a gene with two different alleles

10. Terms cont. Homozygous An animal that carries a gene with two identical alleles

11. Characteristics of Genes Traits are controlled by genes Genes have different forms which are known as alleles In diploid organisms, like man and the higher animals, there are TWO alleles – one on each chromosome of the homologous pair One of each of the above example alleles could be found on a pair of homologous chromosomes

12. Dominant Genes A dominant gene covers (masks) the presence of other genes Capital letters are used to designate dominant genes

13. Recessive Genes A recessive gene is the one over-ridden by the dominant gene For a recessive trait to appear (phenotypically) the animal must be homozygous (have two of the same gene – one on each homologous chromosome) for that characteristic to appear Recessive genes are designated by small letters

14. Examples of Dominant and Recessive Writing Bb Dominant trait Recessive trait Rr Dominant trait Recessive trait

15. Incomplete Dominance Sometime traits do not have one clear dominant gene or one clear recessive gene In incomplete dominance, traits appear to blend together When crossing a red snapdragon with a white snapdragon, the offspring is pink if incomplete dominance occurs The heterozygous genotype in incomplete dominance appears different than either of the homozygous alternatives white Example: red – pink - white

16. Punnett Squares Parents alleles are: AA and aa AA a a AaAa AaAa AaAa AaAa

17. Phenotypic and Genotypic Ratios Phenotypic Ratios Shows ratio of what is seen Example: previous Punnett square: the phenotypic ratio is 2:2 or 1:1

18. Phenotypic and Genotypic Ratios Genotypic Ratios Shows what is is seen and what is not seen Example: previous Punnett square: the genotype ratio is 0:4:0

19. Example Angus cattle: coat color B is dominant b is recessive cross a BB cow with a bb bull B B b b BbBb BbBb BbBb BbBb

20. Example cont. All of the offspring have a black phenotype only Cross a BB cow to a Bb bull. But also, another allele is considered. Polled: P is dominant p is recessive Cross the Bb heterozygous polled bull with the BB homozygous recessive polled cow BPBP Bull - BbPp BpBpbPbPbpbp Cow - BBpp BpBp BpBp BBPp BBpp BBPpBBpp BbPpBbPp BbPpBbPp Bbpp

21. Example cont. BBPp – black polled BBpp – black horned BbPp – black polled Bbpp – black horned Phenotypic Ratio 8:4:4 Or 2:1:1 Genotypic Ratio 4:4:4:4 Or 1:1:1:1