Lecture 4 - Mendelian Inheritance Part 2 1 Last Time...

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Unformatted text preview: Mendelian Inheritance Part 2 1 Last Time Mendel’s contribution to Genetics Why peas?! The mono-hybrid cross The di-hybrid cross Fundamental principles of genetics A quick look at Mendel’s hallmark paper 2 Mendelian Inheritance Pt 2 Pedigree analysis Predicting inheritance outcomes Sum Rule, Product Rule, Binomial Expansion Assessing the validity of genetic hypothesis Chi Square test 3 Huntington’s www.thehavenstudios.co.uk/hannah_002.jpg Cystic Fibrosis wikipedia.org Albinism universe-review.ca/I10-10-polydactyly.jpg graphics.jsonline.com/graphics/badger/img/ may02/5martin506.jpg Polydactyly HUMAN GENETIC DISEASE 4 Pedigrees GENERATION 1ST MALE FEMALE 2ND NORMAL AFFECTED HET 3RD 5 Pedigree analysis /WWW.UIC.EDU/CLASSES/BMS/BMS655/GFX/PEDIGREE1.GIF *Assume disease allele is rare in a population. 6 How can we predict genetic outcomes? HTTP://WWW.GEN.VCU.EDU/IMAGES/COUNSELING.JPG 7 Predicting outcomes Using probability calculations - a quick way to determine probable outcomes in offspring without Punnett Squares Sum Rule Product Rule Binomial expansion equation /WWW.USMONEYRESERVE.COM 8 Sum Rule - addition Predicts outcome of any one of two or more mutually exclusive events Example: If Tt x Tt - what’s the probability of Tt progeny? 9 Sum Rule (from book) Cross: DdCc X DdCc Question: What’s the probability that an offspring will have [either normal ears and a normal tail or droopy ears and a crinkly tail]? D - normal ears d - droopy ears C - normal tail c - crinkly tail 10 Product Rule multiplication Predicts outcome of two or more independent outcomes Example: If Mm X Mm, what is the likelihood that the first born offspring will be MM and the second offspring will be mm? 11 Product rule (from book) Disease: Congenital analgesia - pp Normal - PP, Pp Cross: Pp X Pp Question: What’s the probability that first offspring will have the disease, second will be normal, and the third will also have the disease? 12 Binomial expansion equation Predicts outcome of an unordered combination of events General Example: What’s the probability that two of five kids in the family will have the disease? 13 Binomial expansion equation n! x q(n-x) P= p x! (n-x)! n = total number of events x = number of events in one category p = individual probability of x q = individual probability of other category 14 Example Step 1: Write genotypes (assign letters) Step 2: Write out the cross Step 3: Identify variables in equation (what are the categories?) n= x= p= q= 15 n! x q(n-x) P= p x! (n-x)! Assessing the validity of genetic hypothesis Chi Square Test “Are the data (observation) consistent with our hypothesis (prediction)?” Why is this important? sometimes genes of interest *don’t* follow Mendelian inheritance HTTP://WWW.DKIMAGES.COM/DISCOVER/PREVIEWS/787/261470.JPG 16 Chi Square Test (O 2= Σ Χ E 2 E) (O + E 2 E) + …. category 1 category 2 (ex. phenotype 1) (ex. phenotype 2) Σ = sum calculation for each category O = observed data in this category E =expected data in this category 17 Applying Chi Square to Mendel’s pea data F2 Data (Observed): 315 round and yellow 101 wrinkled and yellow 108 round and green 32 wrinkled and green 556 seeds in all The Hypothesis (Prediction): outcomes will show a ratio of 9:3:3:1 dihybrid cross 18 Calculate each category (315 (108 2= Σ + Χ 104 312 Round, Yellow 2 312) 2 104) + …. Round, green (101 (32 + 35 104 wrinkled, Yellow 2 104) 2 35) wrinkled, green 19 Chi Square table 20 Summary Pedigrees map inheritance patterns of disease throughout many generations Sum Rule, Product Rule, Binomial Expansion predict inheritance outcomes, serve as a hypothesis Chi Square test assesses the validity of a genetic hypothesis 21 Ungraded problems Chapter 2: Go through S1, S4 and S6 to get a feel for how to work these problems. Chapter 2: Try C13, C14, C16, C27, C33 22 Next Time Chromosome structure and mitosis HTTP://WWW.CS.STIR.AC.UK/~PGO/GA/IMAGES/CHROMOSOME_REAL.JPG 23 ...
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