Genetics: a ‘how to’ guide

1. Genetics: a ‘how to’ guide Doing sums step by step

2. Step 1: the data • Write down the data schematically • Leave ‘unknown’ open • Phenotypes and genotypes are important P: ....... X ……. phenotypes . . . . genotypes F1: 57 Long . . F2: 631 Long . . 217 Short . .

3. Step 2: fill in what you know • Fill in the alleles you know from the data • Like: Long is dominant, so all long flies have at least one T • Leave open what you don’t know right away P: ....... X ……. phenotypes . . . . genotypes F1: 57 Long . . F2: 631 Long . . 217 Short . .

4. Step 2: fill in what you know • Fill in the alleles you know from the data • Like: Long is dominant, so all long flies have at least one T • Leave open what you don’t know right away P: ....... X ……. phenotypes . . . . genotypes F1: 57 LongT . F2: 631 LongT . 217 Shortt t

5. Step 3: going back and forth • Use one generation to conclude about the former or the next generation • Like: short (tt) can only pass on short (t) • Leave open what remains unknown P: ....... X ……. phenotypes . . . . genotypes F1: 57 Long T . F2: 631 Long T . 217 Short t t

6. Step 3: going back and forth • Use one generation to conclude about the former or the next generation • Like: short (tt) can only pass on short (t) • Leave open what remains unknown P: ....... X ……. phenotypes . . . . genotypes F1: 57 Long T . F2: 631 Long T . 217 Short t t

7. Step 3: going back and forth • Use one generation to conclude about the former or the next generation • Like: short (tt) can only pass on short (t) • Leave open what remains unknown P: ....... X ……. phenotypes . . . . genotypes F1: 57 Long T t F2: 631 Long T . 217 Short t t

8. Step 3: going back and forth • Use one generation to conclude about the former or the next generation • Like: short (tt) can only pass on short (t) • Leave open what remains unknown P: ....... X ……. phenotypes . . . . genotypes F1: 57 Long T t F2: 631 Long T . 217 Short t t

9. Step 3: going back and forth • Use one generation to conclude about the former or the next generation • Like: short (tt) can only pass on short (t) • Leave open what remains unknown P: ....... X ……. phenotypes . . . . genotypes F1: 57 Long T t F2: 631 Long3TT/ Tt 217 Short 1t t

10. Step 4: more conclusions • Use one generation to conclude about the former or the next generation • Like: only Long (Tt) in F 1 means P1 gives T and P2 gives t • Leave open what remains unknown P: ....... X ……. phenotypes . . . . genotypes F1: 57 Long T t F2: 631 Long 3 TT / Tt 217 Short 1 t t

11. Step 4: more conclusions • Use one generation to conclude about the former or the next generation • Like: only Long (Tt) in F 1 means P1 gives T and P2 gives t • Leave open what remains unknown P: ....... X ……. phenotypes TTt tgenotypes F1: 57 Long T t F2: 631 Long 3 TT / Tt 217 Short 1 t t

12. Step 4: more conclusions • Try and finish by filling in the rest • Like: TT is Long and tt is short P: ....... X ……. phenotypes TT t t genotypes F1: 57 Long T t F2: 631 Long 3 TT / Tt 217 Short 1 t t

13. Step 4: more conclusions • Try and finish by filling in the rest • Like: TT is Long and tt is short P:LongXShortphenotypes TT t t genotypes F1: 57 Long T t F2: 631 Long 3 TT / Tt 217 Short 1 t t

14. Step 5: check your work • Check the genotypes and ratio’s • TT x tt always leads to Tt • Check the phenotypes against the genotypes • Only tt is short winged P:Long X Short phenotypes TT t t genotypes F1: 57 Long T t F2: 631 Long 3 TT / Tt 217 Short 1 t t