Teacher Guide

Genotypes, Phenotypes, Genetics, Oh my!

GEMS 11/04/2017

Standards

SC.7.L.16.2 Determine the probabilities for genotype and phenotype combinations using Punnett Squares and

pedigrees.

SC.912.L.15.15 Describe how mutation and genetic recombination increase genetic variation.

Objectives

Introduce how some traits are inherited by Mendelian genetics

Predict genotype and phenotype using Punnett squares

What are Traits?

Traits are characteristics you inherit from your parents. Ask students to identify traits in the 3 individuals in the figure

below (eye color, skin color, height, freckles).

You should mention that not all traits are visible. A useful video can be found at

http://learn.genetics.utah.edu/content/basics/traits/

Tasting trait

Have students determine what their trait (bitter or not) is for tasting PTC (phenylthiocarbamide). Tasting strips are

available at Amazon.com https://www.amazon.com/Nasco-PTC-Paper-Strips-Vial/dp/B001D7FF5E

To explore more about PTC tasting http://learn.genetics.utah.edu/content/basics/ptc/

Genetics

A gene carries the information (DNA) that determines traits. In the field of genetics, we can predict some of the traits

a child will have if we know the parents’ genes. [For more information on genes & DNA,

http://learn.genetics.utah.edu/content/basics/dna/]

Show the following video to introduce Mendelian genetics: https://www.youtube.com/watch?v=Mehz7tCxjSE

Review all of the definitions in the video before practicing Punnett squares:

1. Traits are characteristics you inherit from your parents.

2. A gene carries information (DNA) that determines your traits.

3. Alleles are different variations of a gene. There are 2 alleles for every gene.

4. The 2 alleles for a gene that represents a specific trait are called genotype.

Ex) The genotype Bb represents hair color

5. Homozygous: the alleles are the same for a particular trait

Ex) BB, bb

6. Heterozygous: the alleles are different for a particular trait

Ex) Bb

7. Phenotype is the observable characteristic of a specific trait resulting from its

genotype.

Ex) Blonde hair is the phenotype observed determined by genotype Bb

8. A dominant trait “hides” the recessive trait in the phenotype of an individual. A capital letter represents

the dominant form in an allele.

9. A recessive trait describes a trait that is covered over (or dominated) by another form of that trait and

seems to disappear. A lowercase letter represents the recessive form in an allele.

Punnett squares

The Punnett square is a way of working out the possible genotypes and phenotypes of offspring.

We use two letters to represent the genotype. A capital letter

represents the dominant allele and a lowercase letter is the

abbreviation for the recessive allele.

In the example on the left, B=dominant, blue and b= recessive

red.

Have students practice the definitions using the Punnett square above.

1. What is the trait?

color

2. What are the alleles?

B and b

3. What are the 3 different genotypes of the offspring?

Bb, BB, bb

4. Which genotypes are homozygous?

BB and bb

5. Which genotypes are heterozygous?

Bb

6. What are the phenotypes of each offspring?

Bb=blue; BB=blue; bb=red

How to generate a Punnett square:

Walk students through constructing a Punnett square using the PTC tasting gene. This demonstrates to students that

by knowing the parents’ genotypes for the PTC tasting gene, we can predict their kids’ ability to taste PTC.

Ask students if the kids of these parents will be able to taste PTC.

Answer: Yes, since the all genotypes have the dominant allele “T”.

TT

T

T

t t

Tt

Tt

Tt

TtGenotype=TTPhenotype=cantastePTCHomozygousDominant

Genotype= Phenotype=cannottastePTCHomozygousRecessive

heterozygous

heterozygousheterozygous

heterozygous

1. Put one letter (allele) above/next to each box. It does not

matter which parent’s genotype goes on the top/side.

2. Fill in the boxes by copying the column & row letters down and

across

Fillintheboxesbycopyingthecolumn&rowle ersdown&acrossintotheemptyspaces.

Practice filling in a Punnett square

Fill in the Punnett square below and use the results to answer the questions below.

Questions:

1. What are the phenotypes of each kid?

2. Which kids will be able to taste PTC?

3. Which kids will NOT be able to taste PTC?

Tt

Genotype=TtPhenotype=cantastePTCHeterozygousDominant

Genotype= Phenotype=cannottastePTCHomozygousRecessive

Mutations

Sometimes mutations can occur in the DNA of specific genes that changes the phenotype. Most mutations are not

bad but just different.

A useful video for mutations http://learn.genetics.utah.edu/content/basics/mutation/

Tt

T

t

t t

ANSWERS

Genotype=TtPhenotype=cantastePTCHeterozygousDominant

Genotype= Phenotype=cannottastePTCHomozygousRecessive

Tt Tt

heterozygous heterozygous

homozygous homozygous

Cantaste Cantaste

CanNOTtaste CanNOTtaste

Use Punnett squares to design a unicorn suncatcher

In groups, students will be assigned genotypes of unicorn “parents” for various traits and create Punnett squares.

Possible traits and genotypes are listed below. The trait “4 or 2 legs” refers to unicorns standing on four or two legs

(https://www.amazon.com/Plastic-Unicorn-Suncatchers-24-Pack/dp/B01KU3AAA6). Students will put the resulting

individual squares into cups labeled with each trait. Students will pick a random square from each trait and use that

phenotype to design their suncatcher. An example of the parent traits and one pair of genotypes is shown below.

The Punnett squares for each trait for Group 1 parent unicorns can be found at the end of this document. You can

include a mutation square in the cup and indicate the phenotype.

Student directions:

1. With a partner, pick one piece of paper from the cup labeled “TRAITS”. Write down the trait you picked.

TRAIT: ______________________________________

2. With your partner, create a Punnett square for the trait you selected. Use the piece of paper from your TA

and follow the directions on it.

Trait DominantAllele RecessiveAllele

4or2legs L l

BodyColor B=silver b=pink

HoofColor H=blue h=purple

TailColor T=purple t=yellow

HornColor W=pink w=black

ManeColor M=green m=blue

Group 4or2legs Bodycolor Hoofcolor Tailcolor Horncolor Manecolor1(father) LL Bb Hh TT ww Mm1(mother) ll Bb HH TT Ww mm

2(f) 2(m)

3(f) 3(m)

4(f) 4(m) 5(f)

5(m) 6(f) 6(m)

3. Once your table has created all the Punnett squares and put each individual square in the appropriate trait

cup, pick one square from each trait cup and write down the genotype and phenotype below.

PUT THE PAPER BACK IN THE CUP SO THE NEXT PERSON CAN PICK!!!

4. Once you’ve finished selecting all traits, use the markers to create your unicorn suncatcher. Make sure your

unicorn matches the phenotype!!!

5. Choose a piece of string so you can hang your suncatcher up!

Trait Genotype Phenotype

Standingon4or2legs

Bodycolor

Hoofcolor

Tailcolor

Horncolor

Manecolor