11.2 Probability and Punnett Squares
Probability
• The likelihood that a particular event will occur is probability
Probability• Example: flipping a coin– 50% chance you will get heads, 50% chance you will
get tails– Also called a 1 in 2 chance (1/2)
Probability• IMPORTANT: Each event does not effect the
event before or the event after– You have EXACTLY the same probability each time
Probability of Many Events
• Multiply the probabilities for each flip.
• Example: if you want to see what your probability is to get heads 3 times in a row, you would calculate (½) x (½) x (½) = 1/8
Probability and Genetics
• The principles of probability can be used to predict the outcomes of genetic crosses.
• Example: predict the offspring of a cross between two individuals.
Probability Activity• State the question and hypothesis.• Answer the pre-activity questions together as a class.• Flip a coin 100 times.• Record how many times the coin landed on heads and how
many times the coin landed on tails.• Calculate the frequency (totals) of heads and tails.• Calculate the percentage of heads and tails.• Answer the post-lab questions.
Probability Worksheet
• Things to remember:–One event does NOT effect a later event–Probability of multiple events, you must
multiply each probability
Punnett Squares
1. Punnett Squares• Diagram used to
determine the results of a genetic cross
Punnett Squares• Genes have two different
possibilities– Two different alleles– These alleles separate
during gamete formation (segregation)
2. Terminology• Dominant Allele: the
trait that will always be seen if it is present– It is “stronger” than
the recessive trait– Represented by a
capitol letter
Terminology
• Recessive Allele: the trait that will only be seen if a dominant allele is not present– Overpowered by
dominant alleles– Represented by a lower
case letter
Phenotype and Genotype
• Phenotype– Physical
characteristics• Example: hair
color, height, eye color
• Genotype– Genetic makeup
Phenotypes and Genotypes
• Important: Some individuals may have the same phenotype with different genotypes– Example: Aa will look like AA• Same phenotype but different genotypes!
Terminology• Homozygous: two identical alleles for a trait– Also called “pure”– “homo-” means “same”
Terminology• Heterozygous: two different alleles for a trait– Considered “hybrid” for that trait– “hetero-” means “different”
Dominant and Recessive• Homozygous dominant: two dominant alleles– Will show the dominant trait– Example: AA
• Homozygous recessive: two recessive alleles– Will show the recessive trait– Example: aa
• Heterozygous– One dominant and one recessive allele– Will show the dominant trait– Example: Aa
Practice with Genetics Terminology
• Get a piece of paper.• Cut the paper into 4 sheets.• On each sheet write:– Two sheets with a capitol A– Two sheets with a lower case a
• Terms: Heterozygous, Homozygous, Homozygous recessive, Homozygous dominant
Punnett Squares
1. Baby Steps Through the Punnett Square
• Determine the genotypes of the parents• Write down your cross• Draw a punnett square• Split the letters of the genotype for each parent and put them
outside the punnett square• Fill in the punnett square to determine the genotypes of the
offspring• Summarize – percentages of genotypes and phenotypes
(these may be different percentages!)• Keep on practicing!
Making Babies!
• This activity involves using the terms we just learned in order to create an individual with each trait.
• Once you have gotten each trait, you will draw your baby.
• Yes, you may name it!
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