Transcript 11.2 Probability and Punnett Squares

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
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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
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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!