1 / 16

Genetic Probabilities

This class provides a comprehensive understanding of genetic probabilities, focusing on dihybrid crosses and carrier calculations. By the end of the session, you'll grasp the purpose of dihybrid crosses, how to determine the likelihood of an unaffected individual being a carrier for a recessive disorder, and the concept of rare-allele assumption. You'll also explore chromosomal linkage and utilize Punnett squares to calculate probabilities. Engage in practical examples and pedigree analysis to reinforce your learning and uncover the complexities of genetic inheritance.

steven-meyers
Télécharger la présentation

Genetic Probabilities

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Genetic Probabilities

  2. Learning Objectives By the end of this class you should understand: • The purpose and nature of dihybrid crosses • How to calculate the probability that an unaffected person may be a carrier for a disorder • What a rare-allele assumption is for • Identify examples of chromosomal linkage

  3. Probability • A probability is a number that represents the number of outcomes that fit a certain definition • All probabilities are between 0 and 1 • 0 = never happens, 1 = always happens • Probabilities may be derived from Punnett Squares • Number of particular outcomes divided by total number of outcomes

  4. Independent Probabilities • When two effects do not interact, they are said to be independent • The assortment of chromosomes during meiosis is independent and follow's Mendel's Law of Independent Assortment • Two genes on the same chromosome are not independent • Chromosomal linkage

  5. Probability of Carrier • If an individual has a family history of a recessive allele, that individual may be a carrier even if they are healthy • If we make the rare allele assumption we can assume it has not been introduced by any other pairings • Probabilities can be influenced by additional knowledge

  6. Multiple Punnett Squares • If someone's genotype is unknown, you may use each genotype to make a separate Punnett Square • Assume “Aa” and “AA” for that individual • Draw separate Punnett Squares for each crossing ? 2/3 1/3

  7. Rare Allele Assumption • If an unknown person has no family history of the disorder, you may instead assume they are homozygous dominant • This is the rare-allele assumption ? 2/3 1/3

  8. Actual Example of Probability • Individual #1 has brown eyes • Individual 1's father has brown eyes, as does his entire family • Individual 1's mother has light blue eyes • Individual #2 has brown eyes • Individual #2's parents both had brown eyes • Individual #2's maternal grandfather had blue eyes • Using the rare allele assumption, what is the probability that #1 x #2 can produce blue eyes?

  9. Probability Level: Expert

  10. Dihybrid Crosses • A dihybrid cross should have the same probabilities as each individual cross separately • Independence • Chromosomal linkage violates the independence pattern • Closely resembles a single Punnett Square for both alleles • Why not exact?

  11. Crossing Over • Imagine an X chromosome with both hemophilia and red-green colorblindness • Use this X chromosome as X' in the following cross: • XY x X'X • With crossing over in Meiosis Prophase I, the X woman's X chromosomes trade some genes • May then become XY x XHXC for hemophilia and colorblindness separately

  12. Dihybrid Practice • Perform a dihybrid cross: AaX'Y x AaX'X • Assume X' is a recessive defect. What is the probability that a boy will have the disorder? What is the probability that a girl will have the disorder? • What is the probability that a child will have both?

  13. Is This Necessary? • The answers were obtainable by using individual Punnett Squares! • The rules may get more complicated: • Perform a AaZz x AaZz cross with the following phenotype rules: • If zz, individual is black • If has a dominant Z, individual phenotype depends on A: • If AA, individual is red • If Aa, individual is brown • If aa, individual dies at birth • Will see more polygenic traits in later chapters

  14. Pedigree Practice • Draw the pedigree for the following information: • Mother healthy, father afflicted, four children • 1st child: Boy, healthy, married, two healthy sons • 2nd child: Girl, healthy, married, one afflicted son, one healthy daughter, one healthy son • 3rd child: Girl, healthy, married, one afflicted son, two healthy daughters • 4th child: Boy, healthy, married, one healthy daughter • What is the pattern of inheritance?

  15. Pedigree Practice • Everyone choose one of the five patterns and draw your own pedigree chart! • Be sure it has at least 3 generations and there should be at least five crosses of interest • Trade with a partner and analyze which pattern(s) it matches!

  16. See you for the exam tomorrow!

More Related