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Plantfairies and plantmonsters: Adventures in Mendelian geneticsFeatured science projectScience project video

Procedure

Our imaginary scientists from "Plants-R-Us, Inc." have been experimenting with genetic engineering of plants to use in biocontrol projects. Their intention was to create a carnivorous plant, called "plantfairies", similar to Venus Flytraps, pitcher plants and sundews, which get nutrients by consuming insect pests like mosquitos.

Something terrible happened and a bizarre mutation appeared in the third generation of engineered plants that allows them to grow giant flowers with sharp, dangerous teeth, and a preference for eating human beings, - these mutant plants have been named "plantmonsters". The plantfairies are harmless dwarf flowers with "tongues" that "flick", to catch insects.

All plantmonsters are going to be destroyed by specially trained members of our research team; however, many plantfairies still remain. Some plantfairies are carriers of the dangerous plantmonster genes and can pass the gene on to future generations. Millions of dollars have gone into this research and our scientists want to know if any plantfairies can be salvaged for the purpose of mosquito control. It's your job to make predictions about the offspring of these mutant plants in order to prevent the world being taken over by these plantmonsters!!

You will need the included tables of plantfairy and plantmonster genotypes and phenotypes. Remember, plantfairies are dwarves with "frog tongues", while plantmonsters are giants with "dagger teeth". A dwarf with dagger teeth is still dangerous because it eats small mammals and birds, and carries the alleles for dagger teeth.

Trait

Dominant (homozygous)

Recessive (homozygous)

Heterozygous (Dd, Tt)

Body size

dwarf

giant

dwarf

Mouthparts

frog tongue

dagger teeth

frog tongue

 

 

   

Dominant

Recessive

Trait

Alleles

Genotype

Phenotype

Genotype

Phenotype

Body size

D,d

DD, Dd

Dwarf

dd

Giant

Mouthpart

T,t

TT, Tt

frog tongue

tt

Dagger teeth

Plantmonsters - Mendelian genetics Plantmonsters - identifying the genotypes and alleles

1) The scientists have begun breeding experiments to determine the genotypes of the remaining plantfairies and identify any individuals who may be carrying the dangerous recessive alleles. They have isolated plantfairy #156 for you, so you can perform a testcross with a purebred plantfairy in order to determine its genotype. Purebred plantfairies have known genotypes that are homozygous dominant for all traits, so they are "dwarf" flowers with "flicking" tongues, that are able to catch insects.

When you perform the testcross of a purebred plantfairy with plantfairy #156, all offspring are homozygous dominant for all traits. Given these results, what genotype does plantfairy #156 have? The results of the dihybrid testcross are shown in the punnett square below. Since you know the genotypes of all offspring and the purebred, you work backwards to solve the genotype of plantfairy #156. Is plantfairy #156 safe to keep in the population?

   

Alleles from Plantfairy #156

Alleles from purebred plantfairy

 

??

??

??

??

 DT 

DDTT

DDTT

DDTT

DDTT

 DT 

DDTT

DDTT

DDTT

DDTT

 DT 

DDTT

DDTT

DDTT

DDTT

 DT 

DDTT

DDTT

DDTT

DDTT

           

2) Next, scientists want to know what possible genotypes will result from a cross between a purebred plantfairy and a plantfairy carrying the dangerous recessive alleles. They give you one purebred plantfairy (DDTT) and one heterozygous plantfairy (DdTt) to cross. Use punnett squares to show the possible genotypes that will result from such a cross and calculate the probability of getting each genotype. Set up a punnett square for a dihybrid cross as demonstrated in the background section. Remember to use F.O.I.L. to determine all combinations of alleles that each parent can pass on to offspring. Draw pictures of the offspring if it helps you to determine the proportions or ratio of each phenotype resulting from this cross.

 

Alleles from purebred plantfairy

DT

DT

DT

DT

Alleles from heterozygous plantfairy

  dT  

DdTT

DdTT

DdTT

DdTT

  dt

DdTt

DdTt

DdTt

DdTt

  Dt

DDTt

DDTt

DDTt

DDTt

  DT

DDTT

DDTT

DDTT

DDTT

Offspring Phenotypes:

Dwarf, Tongue: _________________

Dwarf, Teeth: _________________

Giant, Tongue: _________________

Giant, Teeth: __________________


3) Now the research team wants to know how many of the offspring can be saved that result from crossing two heterozygous plantfairies (DdTt). Follow the instructions in step 2, but this time both parents are heterozygous. Draw pictures of the offspring if it helps you to quantify how many of each type of phenotype will result from this pairing.


 

Alleles from heterozygous plant 1

DT

dt

dT

Dt

Alleles from heterozygous plant 2

DT

DDTT

 

DdTt

DdTT

DDTt

dt

DdTt

ddtt

ddTt

Ddtt

dT

DdTT

ddTt

ddTT

DdTt

Dt

DDTt

Ddtt

DdTt

DDtt

Offspring Phenotypes:

Dwarf, Tongue: _________________

Dwarf, Teeth: _________________

Giant, Tongue: _________________

Giant, Teeth: __________________


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