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Probability and Multiple Trait Inheritance. Punnett Squares and Probability. All ratios established from a Punnett square, represent probabilities. Probability can be thought of as a score out of 1 that indicates the likelihood of an event. 0.50 event will occur half of the time
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Punnett Squares and Probability • All ratios established from a Punnett square, represent probabilities. • Probability can be thought of as a score out of 1 that indicates the likelihood of an event. • 0.50 event will occur half of the time • 1.00 event will occur all of the time • Product Law: The probability of two or more outcomes occurring is equal to the product of their individual probabilities.
Monohybrid Crosses • Thalassemia is an autosomal recessive condition that affects hemoglobin production and can cause anemia in affected persons H = normal hemoglobin h = thalassemia • Consider two parents, both heterozygous for thalassemia: Hh X Hh, what is the probability that they will have an affected child?
Practice • What is the probability of a couple having 3 female children? • If a couple has 2 children, what is the probability they will have a boy and a girl? • If their first child is a girl, what is the probability that the next two will be girls?
Probability and Pedigrees • The pedigree traces the occurrence of deafness throughout a family. • If individual IV-2 marries a deaf woman, what is the probability that any of their children will be deaf?
When analyzing risk based on a pedigree, correctly determining the mode of inheritance is key to making an accurate prediction. • Determine the mode of inheritance in each case:
Dihybrid Crosses • In cocker spaniels: • black coat colour (B) is dominant to red (b) • solid colour (S) is dominant to white spotting (s). • If two dogs, heterozygous for both traits are mated, what is the probability they will have red offspring with white spotting?
Warm up • In mice, black coat (B) is dominant to white coat (b) and black eyes (E) are dominant to pink eyes (e). • A male, heterozygous for both traits, is mated to a pure-breeding recessive female. • Show the genotypes for each parent • Show the possible sex cells each parent could produce • Construct a Punnett square to determine all possible genotypes and phenotypes in the F1 generation.