Probability and Punnett Squares – notes
Topic
Probability
Punnett
Square
Details
• A concept that can be used to ____________the results of a particular event
–
Examples
•
Chance of a specific team winning a sporting event
•
Chance of a coin landing on heads in a coin toss
– Predict what is ______________ to occur, not necessarily what will actually occur
•
___________________________ – A chart that shows how parents’ alleles might combine in an offspring
– a tool that can help you understand the ______________ of heredity
–
Geneticists use Punnett Squares to show all the
_____________________ outcomes of a genetic cross and to determine the probability of a particular outcome
Using a
Punnett
Square
What is the probability of…..
• The offspring having a yellow seed color?
________ or ________
–
The offspring having a green seed color?
_______ or ________
In rabbits, black fur color is dominant to white. What is the probability of producing a white rabbit if two heterozygous rabbits mate? ____________
Step 1: Figure out the genotype of the parents.
•
Black is dominant to white.
– B - ______________
– b - ______________
•
Parents are heterozygous.
– _________ - dad
–
_________- mom
Step 2: Set up a Punnett Square.
Step 3: Fill in the Punnett Square.
Step 4: Count the results.
•
Genotypes
–
_____ homozygous dominant
–
_____ heterozygotes
–
_____ homozygous recessive
•
Phenotypes
– _____ black fur
–
_____ white fur

Ratios
•
Probability can also be represented in _______________
– A ratio ___________________ or shows the relationship between a part to the whole
•
Example the probability that a coin will land on heads in a single coin toss is 1 in 2 or 50%
–
As a ratio, the probability would be written as 1:2 and would be read as, “One to two.”
–
In _________________ we use rations to represent probability
•
Genotypes
–
1 homozygous
– dominant
2 heterozygotes
–
1 homozygous recessive
– Genotypic Ratio = ____
•
Phenotypes
–
3 black fur
– 1 white fur
–
Phenotypic Ratio = ___
Practice In pine trees, long needles are dominant over short needles. Cross a homozygous dominant plant with a plant that is heterozygous. What is the probability that the parents will produce offspring that have short needles? Give the genotypic and phenotypic ratios.
Probability of short needles: ________
Genotypic Ratio: _________________
Phenotypic Ratio: ________________
2. In cats, a striped coat is dominant over a solid coat. Cross a cat with a solid coat with a cat that is heterozygous for a striped coat. What is the probability that the parents will produce offspring with a solid coat? Give the genotypic and phenotypic ratios.
Probability of solid coat: ________
Genotypic Ratio: _________________
Phenotypic Ratio: ________________
3. In humans, dark hair is dominant over light hair. Cross a man that is homozygous recessive with a woman that is homozygous dominant. What is the probability that the parents will produce offspring with light hair? Give the genotypic and phenotypic ratios.
Probability of light hair: ________
Genotypic Ratio: _________________
Phenotypic Ratio: ________________