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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!