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2. Lab 1 Probability &amp; Statistics (Sept. 21-25)

# 2. Lab 1 Probability &amp; Statistics (Sept. 21-25) -...

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BIOL 2040 14 DRY LAB – PROBABILITY & STATISTICS Expectations Upon completion of this lab, you should be able to: Explain what probability is and its importance Calculate chi-square. Describe the differences between the product and sum rules with respect to probability. Explain how Punnett squares show probabilities. Reading Hartwell et al., (2008) Tools of Genetics: The Chi-Square Test p128-129 (read only the boxed information) Hartwell et al., (2008) review if necessary: Punnett squares, Ch. 2; Meiosis, Ch. 4 Required Materials Two coins (any denomination). Material Covered on Quiz Material within this lab Due Hand-in assignment sheet (answers to questions 1-18 within this lab) – due at end of lab. INTRODUCTION Probability theory and its application in statistics are central to genetics research. Given a specific hypothesis, geneticists are often concerned with determining the probability of a genetic event happening (i.e., observing certain genetic data), and testing whether data are consistent with the hypothesis. Particularly in human genetics, there is interest in predicting the chance of a certain event. For example: What is the chance that a couple will have a child with Tay-Sachs disease? Are two genes found on the same chromosome (i.e., they are “linked”)? What proportion of the population is expected to be a carrier of a disease? All three of these questions require an understanding and application of probability theory. Note that these questions deal with two different ways of thinking about probability: 1) probability as a description of the relative frequency of an event ( e.g., the proportion of a population with a disease), and 2) probability as a prediction of the ‘chance’ of a certain outcome ( e.g., the chance of having a child with a disease). To illustrate probability laws, we’re going to use Punnett squares and the coin toss. Probability Lingo Typically when describing probabilities (‘chances’), we tend to use fractions, rather than percentages. E.g., ½ or 0.5, rather than 50%. If you consider that: ½ + ½ = 1, it makes sense then that the largest (maximum) probability or frequency you can have is 1 (not 100, as in percentages), and the minimum is 0.

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BIOL 2040 15 PUNNETT SQUARE REVIEW The Punnett square, developed in the early 20th century by the geneticist R.C. Punnett (NOT Mendel, or it would be called a Mendel square, which it isn’t), can be used to easily predict the outcome of a specific cross (or mating). The first step in generating a Punnett square is to 1) determine all possible genotypes of gametes produced by both parents – remember gametes are haploid. 2) A table is then made and all the possible different gametic genotypes are listed on the two sides of the square (gametes for one parent are listed in the top row, whereas those for the other parent are listed in the leftmost column) (See Table 1.1). 3) The combination of the different gametes from the two parents can then be used to determine the genotypes of all potential offspring.
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