Probability and Multiple Trait Inheritance

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# Probability and Multiple Trait Inheritance - PowerPoint PPT Presentation

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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### 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
• 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.