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

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Presentation on theme: "Genetics: a ‘how to’ guide Doing sums step by step."— Presentation transcript:

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

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

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

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

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

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

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

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

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

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

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

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

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

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


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