1. Genetic Crosses – single gene

2. Genotype and PhenotypeGenotype and Phenotype –Genotype is the genetic makeup of the organism. –Phenotype is the physical appearance of the organism.

3. Heterozygous Vs Homozygous HomozygousHomozygous –Same gene or allele for the pair (AA or aa) HeterozygousHeterozygous –Different genes or alleles in the pair (Aa) Capital letter for dominant, lower case for recessiveCapital letter for dominant, lower case for recessive

4. Probability Likelihood that an event will occur.Likelihood that an event will occur. Can be expressed as a fraction, decimal, or a percentage.Can be expressed as a fraction, decimal, or a percentage. Calculated by:Calculated by: –Prob. = # times event occurs/ # of times opportunity occurred.

5. Crosses Involving 1 Pair of Genes percent outcomes P = TT x TTP = TT x TT –100% tall P = TT x TtP = TT x Tt –100% tall P = TT x ttP = TT x tt –100% tall P = Tt x ttP = Tt x tt –50% tall, 50% short P = Tt x TtP = Tt x Tt –75% tall, 25% short P = tt x ttP = tt x tt –100% short Memorize these crosses – it will save you time.

6. Crosses Involving 1 Pair of Genes Punnett squares T.5 t.5 T.5 t.5 TT Tt T t t t P = Tt x Tt Gametes of 1 parent (1N) Gametes of the other parent (1N) What is inside the box are the prosible results of fertilization (2N)

7. Test Cross – a breeding experiment Pair share: How could you determine if a black guinea pig is heterozygous or homozygous?How could you determine if a black guinea pig is heterozygous or homozygous? (black is dominant over white)(black is dominant over white) Hint look at the outcomes of different crosses….Hint look at the outcomes of different crosses…. B = Black b = white (answer on next slide)

8. Test Cross P = B? xP = B? x bb If F1 is 100% black then genotype of unknown parent is BB If F1 is 50% black and 50% white then unknown parent is Bb. X

9. P = Bb x bb P = BB x bb B B b b Bb bB Bb Bb Bb b b B B b b b bb b

10. Incomplete Dominance X = RR WW X = RW Neither “R” allele or “W” allele is dominant. Phenotype is intermediate.

11. Incomplete Dominance X = RW X Neither “R” allele or “W” allele is dominant. Phenotype is intermediate. 25% RR 25% WW 50% RW

12. Codominance When neither genotype is dominant and both traits are expressed. –Human blood type

13. Review Phenotype? 1.What is Phenotype? 2.What is the probability of getting a white guinea pig if both parents are heterozygous? 3.What is incomplete dominance?