#Title: Plantfairies and plantmonsters: adventures in Mendelian genetics

#Targeted Level: 11th

#Difficulty: Advanced 2

#Time Required: 1 hour

#Notes on Time Required:

#Prerequisites: You need to be familiar with concepts and vocabulary introduced in the science project called “The Odds of Being You: a zoomonster from planet Planktonia”. You also need to understand the concepts of DNA, chromosomes, and genes.

#Material Availability: Readily available

#Material Availability Notes: All the materials for this lab can be found at home.

#Cost: Very low

#Adult Supervision Required: No

#Safety:

#Abstract: In this science project, you are going to explore advanced concepts in Mendelian genetics. Our "research sScientists" have genetically engineered a plant, called "plantfairies", to use to control insect pests. But sSomething went wrong with our experiment, which resulted resulting in a mutant form (called plantmonsters) that are’s dangerous to humans, called plantmonsters. You are going to help the our research team by identifying the genotypes of the plantfairies and their offspring in order to determine which plants may be carrying the dangerous alleles.

#Objective: To gain an understanding of advanced concepts in Mendelian genetics and make predictions using dihybrid crosses.

#Hypothesis:

#Credits:

Jessica Watson, B.S. Ecology & Evolutionary Biology

#Background:

Gregor Mendel was an Austrian monk in the 19 th century who uncovered many of the basic principles of inheritance and genetics by his experiments with pea plants. By observing several generations of the plant, he could determine which traits were dominant and which were recessive, as well as identify several patterns of inheritance. He mated different varieties of plants, using a brush to transfer pollen. Mating different varieties, or crossing different genotypes, of a plant is called hybridization.

Mendel started his experiments with purebred plants, that is, identical plants that when mated had offspring with traits identical to their parents (such as having all purple flowers). Purebreds are homozygous for the trait that they exhibit, such as flower color. They may be homozygous dominant (PP=purple flowers) or homozygous recessive (pp=white flowers). When Mendel crossed purebred purple plants with purebred white plants, all plants in the first generation of offspring were purple. The punnett square for that cross is as follows, using the letter p to represent alleles for flower color:

Alleles from the purebred purple plant

P P

Alle

les

from

the

pure

bred

whi

te

plan

t

p Pp Pp

p Pp Pp

Table 1. Punnett square for monohybrid cross of two purebred plants.

When breeding experiments only follow one trait, such as flower color. , they’reThey are called monohybrid crosses. As you can see from the punnett square above, all offspring produced were heterozygous for flower color. Because they had one dominant allele (P) in their genotype, they all exhibited the dominant purple phenotype. However, when Mendel crossed the heterozygous offspring of two different purebreds, he observed a different pattern of inheritance in this second generation of offspring.

Alleles from heterozygous plant 1P p

Alle

les

from

th

eter

ozyg

ous

plan

t 2

P PP Pp

p Pp pp

Table 2. Punnett square for monohybrid cross of two heterozygous parents.

The second generation of offspring had the following genotypes: PP, Pp, Pp and pp. Instead of having all purple flowers, some offspring had white flowers. Those with a dominant allele (P) had purple flowers, while those with two recessive alleles (pp) had white flowers.

A ratio is a mathematical expression to describe the proportion of different items in a set. If there are 3 boys and 2 girls in a room, the ratio of boys to girls in the room is 3:2. Similarly, the ratio of purple to white flowers, or phenotypes, in the offspring of the heterozygous cross is 3:1. The ratio of genotypes in the offspring is slightly different. Since there were 3 different genotypes in the offspring (1 PP, 2 Pp and 1 pp), the ratio of genotypes is 1:2:1.

Mendel’s breeding experiments became more complicated when he performed crosses to observe more than one trait at once, such as pea color and texture, called dihybrid crosses. Punnett squares for dihybrid crosses are larger. The following will illustrate an example of the punnett square resulting from a dihybrid cross of pea plants, with both parents being heterozygous for pea color (Yy) and pea texture (Rr).

Dominant pea color is yellow (Y), while recessive color is green (y). Dominant pea texture is round (R), while recessive is wrinkled (r). The genotype for both parent pea plants is YyRr. The first step to make this punnett square is to determine the combinations of alleles that each parent can give separately. To do this it’s necessary to use a technique from algebra called F.O.I.L. (first-outer-inner-last) on the genotype YyRr.

The genotype for trait one (pea color) is Yy, while the genotype for trait two (pea texture) is Rr. First, multiply the first letter of each trait’s genotype (Y*R), then the two outer letters (Y*r), then the two inner letters (y*R) and finally the last letters (y*r). These are the four possible combinations of alleles that each parent plant can donate to offspring. To determine the offspring, you cross multiply all four parent alleles. As you can see from the punnett square below, a dihybrid cross results in many more possibilities for the genotype and phenotype of the offspring.

Alleles from heterozygous plant 1YR Yr yR yr

Alle

les

from

thet

eroz

ygou

s pl

ant

yr YyRr Yyrr yyRr yyrr

yR YyRR YyRr yyRR yyRr

Yr YYRr YYrr YyRr Yyrr

2 YR YYRR YYRr YyRR YyRr

Table 3. Punnett square for dihybrid cross of two parents heterozygous for both traits.

#Terms and Concepts:

hybridizationratiomutationmonohybrid crossdihybrid crosstestcross

#Questions:

1. Can you think of any examples of organisms that have undergone a mutation that can be harmful to people?

2. What is a mutation at the genetic level? 3. What causes mutations?

#Bibliography:

#Materials and Equipment:

papercolored pencils

#Experimental Procedure:

Our imaginary Sscientists 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 to be giant flowers with sharp, dangerous teeth, and a preference for eating human beingss, - these mutant plants have been named called "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 the our research team; however, many plantfairies still remain. Some plantfairies are carriers of the dangerous plantmonster genes and can pass itthe gene on to future generations. Millions of dollars went 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 a

world takeoverthe world being taken over by these plantmonsters!! Please help, our survival depends on it!!

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 dwarf giant dwarfMouthparts frog tongue Dagger dagger

teethfrog tongue

Dominant RecessiveTrait Allele

sGenotype

Phenotype

Genotype

Phenotype

Body size D,d DD, Dd Dwarf dd GiantMouthpart T,t TT, Tt frog tongue tt Dagger

teeth

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) ?? (DT) ?? (DT) ?? (DT)DT DDTT DDTT DDTT DDTTDT DDTT DDTT DDTT DDTTDT DDTT DDTT DDTT DDTTDT 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 plantfairyDT DT DT DT

Alle

les

from

het

eroz

ygou

s pl

antfa

iry

dT DdTT DdTTDdTT DdTT

dt DdTtDdTt DdTt DdTt

Dt DDTtDDTt

DDTtDDTt

DT

DDTT DDTTDDTT 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 1DT dt dT Dt

Alle

les

from

het

eroz

ygou

s pl

ant 2 DT

DDTT

DdTtDdTT DDTt

dtDdTt ddtt ddTt Ddtt

dTDdTT

ddTtddTT DdTt

Dt

DDTt DdttDdTt DDtt

Offspring Phenotypes: Dwarf, Tongue: _________________

Dwarf, Teeth: _________________

Giant, Tongue: _________________

Giant, Teeth: __________________

#Discussion: Which cross yields more harmless plantfairies, the cross between a purebred plantfairy and heterozygous plantfairy (step 2) or between two heterozygous plantfairies (step 3)? Which genotypes do you recommend for extermination and why?

#Make it Your Own: Design your own biocontrol breeding experiments that go terribly wrong. Choose two traits in this organism that mutate into a form that’s dangerous to humans. Perform dihybrid crosses as in steps 2 and 3 and analyze your results.

#Answers to Questions:

1. Can you think of any examples of organisms that undergo a mutation that can be harmful to people?

Bacteria regularly mutate such that they become resistant to antibiotics. MRSA, also known as methycillin resistant Staphylococcus aureus, is one such example of bacteria that is resistant to treatment with antibiotics. Treating infections from resistant bacteria is one of the challenges that hospitals face.

2. What is a mutation at the genetic level?

A mutation is a change in the DNA sequence that can be as simple as a change to a single nucleotide, such as a substitution or loss, or a change to more than one nucleotide. It can affect both coding and non-coding segments of the DNA.

3. What causes mutations?

Mutations can occur naturally in the process of replicating DNA for cell division. There are also factors in the environment called mutagens that can cause mutation. Some examples of mutagens are ultraviolet light, certain chemical compounds as well as viruses and bacteria.