Genetic Diversity
True or false
True
True
False
Reproduction
Punnett’s Square
Scientists use a Punnett’s square to determine the possible genetic outcomes for the offspring that result from the combination of the parent’s genes.
Female
Male
Important to know before getting started:
Black colored fur is the dominant trait.
We will use the Punnett’s Square to determine the offspring of guinea pigs. The offspring will either be black or white.
Generation 1
B
B
b
b
In this case we have a dad with black fur and a mother with white fur.
Because black is the dominant gene, we write it with a capital ‘B’.
Generation 1
B
B
b
b
White fur is a recessive trait. It is written with a lowercase ‘b’. It does not matter what letter we choose to represent a gene, but capital letter is always dominant and lowercase is always recessive.
Generation 1
B
B
b
b
To complete the Punnett’s square we combine the gene from mom with the gene from dad. We always write the dominant gene first.
Bb
Generation 1
B
B
b
b
We write the dominant gene first because it “masks” the recessive gene. Therefore, the color of the guinea pig with the genes Bb would be black.
Bb
Generation 1
B
B
b
b
Try and fill out the remaining offspring on your own.
Bb
Generation 1
B
B
b
b
Bb
Bb
Bb
Bb
What color will these guinea pigs be?
Generation 1
B
B
b
b
Bb
Bb
Bb
Bb
100% are heterozygous black.
We will now take one female and one male from this generation to cross for our second generation.
Generation 2
B
b
B
b
What will the gene combinations be for these offspring?
Try to fill out the Punnett’s square.
Generation 2
B
b
B
b
What you have completed is the genotype for all the offspring. Genotype refers to the gene combination that an individual has.
Can you figure out what color these offspring will be?
BB
Bb
Bb
bb
Generation 2
B
b
B
b
What you have just determined is called the phenotype. The phenotype is what we see as a result of an individual's genes.
BB
Bb
Bb
bb
black
black
black
white
Generation 2
B
b
B
b
BB
Bb
Bb
bb
The entire Punnett’s square represents all possible outcomes.
That means each small box represents 25% of the offspring.
What percentage will be white?
Generation 2
B
b
B
b
BB
Bb
Bb
bb
75% are black.
25% are white
Notice: This will always add up to 100%.
¿Cómo puede un conejillo de indias tener pelaje blanco si ambos padres tenían pelaje negro?
How can a guinea pig have white fur if both parents had black fur?
Tongue curling is the dominant trait. T
Non-curling is the recessive trait. t
The ability to curl your tongue is also genetic.
Tongue Curling
T
t
T
T
Copy into your notebook and complete the Punnett’s Square.
What percentage of offspring will be able to curl their tongue?
Tongue Curling
T
t
T
T
100% percent of offspring will be able to curl their tongues.
TT
Tt
TT
Tt
Plastic Egg Genetics
(Complete Dominance)
Each parent is represented by 1⁄2 the egg.
2 parents = 1 whole egg
3. Write down your results for the phenotypes and genotypes of the offspring.
4. Open your egg to check your results.
Do your results match what was in the egg?
Set up your blue/yellow egg
Set up your pink/purple egg
W= white
R = red
WR = pink
Incomplete Dominance
The petal color of pea flowers is an example of incomplete dominance. Both genes for white and red flowers are equally dominant, which results in a new phenotype.
Pea Flower Petals
R
R
W
R
Copy and complete this Punnett’s square in your notebook.
What percentage of offspring will have white flowers?
W= white
R = red
WR=pink
Pea Flower Petals
R
R
W
R
0% of the offspring will have flowers.
50% will have red flowers.
50% will have pink flowers.
WR
WR
RR
RR
Eye color
all other colors-recessive
brown -dominant
Eye color
E
E
e
e
Copy this Punnett’s square into your notebook. Determine both the genotype and phenotype.
What percent of offspring will have brown eyes?
Eye color
E
e
100% percent of offspring will have brown eyes.
Ee
Ee
Ee
Ee
e
E
Eye color
E
e
e
e
Copy this Punnett’s square into your notebook. Determine both the genotype and phenotype.
What percent of offspring will have brown eyes?
Eye color
e
e
50% percent of offspring will have brown eyes.
50% percent of offspring will have blue eyes.
Ee
ee
Ee
ee
e
E