Summary of Aneuploidies Part 6

When to use each rule… Good rule of thumb to use when determining which rule is preferable: ◦ AND versus OR ◦ AND = multiplication rule OR = addition rule If only one option of 2 is possible in a given question = OR If multiple events that are independent or combine repeated events = AND What is the chance that a male and then a female will be born? ◦ Male vs female = OR = addition rule 1 out of 2 ◦ First a male then a female = AND = multiplication rule of the 2 individual probabilties Addition Rule The probability of obtaining one or the other of 2 mutually exclusive events, A or B, is the sum of the separate probabilities Probability of WW or Ww = Probability of WW + Probability of Ww Every time you use a punnet square and say the probabilities of getting particular phenotypes, you are using the ADDITION RULE! Product Rule The probability that two or more independent outcomes will occur is equal to the product of their individual probabilities What is the probability that a couple’s first 3 children will exhibit a recessive trait if both parents are heterozygotes? Aa X Aa Use Punnett Squares! 1. 2. Calculate the individual probabilities Multiply the individual probabilities What is the probability of aa? Then what is the probability of aa happening 3 times? ◦ Probability 1 x 2 x 3 Product Rule Can be used to predict the outcome of a cross involving two or more genes AaBbCC X AabbCc What is the probability that the offspring will be AAbbCc? Probability of AA? Probability of bb? Probability of Cc? P = pAA x pbb x pCc More Complex Probabilities X Consider Mendel’s cross of two heterozygous tall plants. What is the likelihood of having three offspring where two are normal height and one is short? This is more difficult because there are multiple ways this could occur with three offspring. Tall could be TT or Tt = 1/4 + 1/2 = 3/4 or Short must be 1/4. Each grouping is 3/4 x 3/4 x 1/4 = 9/64. 9/64 + 9/64 + 9/64 = 27/64. This can become tedious. or Data Analysis Genetic data analysis makes use of probability and statistics Offspring from crosses are predicted using binomial probability In a binomial experiment there are two mutually exclusive outcomes, often referred to as "success" and "failure". Example: Flipping a coin where ◦ heads = success and ◦ tails = failure If the probability of success is p, the probability of failure is 1 p.; In binomial trials the rate of success is constant (0.5) If the probability of possibility A is p and the probability of the alternative possibility B is q, then the probability that, in n trials, A is realized s times and B is realized t times is n! s t s!t! p q OR n! pxqn-x Probability = x! (n-x)! EXAMPLE TIME MOVING FROM PUNNETT SQUARES TO CHROMOSOME ANALYSIS You hypothesize that an allele is autosomal dominant to another allele. 1 genes with 2 variants that must have distinct phenotypes to evaluate What designation should be used? What are the expected outcomes? What additional experimentation needs to be done to further support your hypothesis? Punnett Squares You hypothesize that 2 genes are UNLINKED with two variants for each gene available. 2 genes with 2 variants must have distinct phenotypes to evaluate What designation should be used? What are the best choices for evaluating the traits and their inheritance? Punnett Squares K and L are designating 2 different genes. There are 2 alleles for each of these genes. What are the potential genotypes for these 2 genes and their 2 alleles? What are the potential gametes if the genes are unlinked? What are the potential gametes if the genes are linked in cis without recombination? With recombination? What are the potential gametes if the genes are linked in trans without recombination? With recombination? Hypothesized Genotype: AaBb on one chromosome (in cis) EeGg on another chromosome (in cis) Draw example chromosomes How would these be inherited in the absence of recombination? How would these be inherited if recombination occurred between A and B? Between E and G? Between both simultaneously?