Introduction to Genetics

2. INTRODUCTION TO GENETICS

6. Definitions: trait: a characteristic that can be passed from parent to offspring heredity: the passing of traits from parents to offspring genetics: the study of heredity

8. Traits in Pea Plants Pea plants have many different traits Some traits are dominant over others Allele: a form of a gene (different bases along the DNA) Dominant: allele that is expressed (regardless of its counterpart allele); represented by a capital letter (e.g. T) Recessive: allele that is expressed only when its counterpart allele is also recessive ; represented by a small letter (e.g. t) Examples of traits in pea plants

11. GENOTYPE AND PHENOTYPE Genotype of alleles: P = purple flower p = white flower All genes occur in pairs, so 2 alleles affect a characteristic Possible combinations are: Genotypes PP Pp pp Phenotypes purple purple white

14. GENERATION “GAP” Parent generation (P1) 1 st filial generation (F1) 2 nd filial generation (F2)

15. BREED THE P1 GENERATION P1 = tall (TT) x short (tt) pea plants T T t t

16. BREED THE P1 GENERATION: SOLUTION P1 = tall (TT) x short (tt) pea plants t t T T Tt Tt Tt Tt All Tt = tall (heterozygous tall) produces the F 1 generation

17. BREED THE F1 GENERATION F1 = tall (Tt) x tall (Tt) pea plants T t T t

18. BREED THE F1 GENERATION: SOLUTION F1 = tall (Tt) x tall (Tt) pea plants T t T t TT Tt Tt tt produces the F 2 generation 1/4 (25%) = TT 1/2 (50%) = Tt 1/4 (25%) = tt 1:2:1 genotype 3:1 phenotype

19. FOLLOWING THE GENERATIONS Cross 2 pure plants TT x tt Results in all hybrids Tt Cross 2 hybrids, results in 3 Tall & 1 Short TT, Tt, tt