Genetics: a ‘how to’ guide

Doing sums step by step

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 . .

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 . .

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 T .

F2: 631 Long T .217 Short t t

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

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

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

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

T t

T TT Tt

t Tt tt

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 3 TT / Tt217 Short 1 t t

T t

T TT Tt

t Tt tt

Step 4: more conclusions

P: ....... X ……. phenotypes . . . . genotypes

F1: 57 Long T t

F2: 631 Long 3 TT / Tt217 Short 1 t t

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

T t

T TT Tt

t Tt tt

Step 4: more conclusions

P: ....... X ……. phenotypes TT t t genotypes

F1: 57 Long T t

F2: 631 Long 3 TT / Tt217 Short 1 t t

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

T t

T TT Tt

t Tt tt

Step 4: more conclusions

P: ....... X ……. phenotypes TT t t genotypes

F1: 57 Long T t

F2: 631 Long 3 TT / Tt217 Short 1 t t

Try and finish by filling in the rest Like: TT is Long and tt is short

T t

T TT Tt

t Tt tt

Step 4: more conclusions

P: Long X Short phenotypes TT t t genotypes

F1: 57 Long T t

F2: 631 Long 3 TT / Tt217 Short 1 t t

Try and finish by filling in the rest Like: TT is Long and tt is short

T t

T TT Tt

t Tt tt

Step 5: check your work

P: Long X Short phenotypes TT t t genotypes

F1: 57 Long T t

F2: 631 Long 3 TT / Tt217 Short 1 t t

Check the genotypes and ratio’s TT x tt always leads to Tt

Check the phenotypes against the genotypes Only tt is short winged

T t

T TT Tt

t Tt tt