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 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 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!