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How come it is powerful helps you determine the

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Unformatted text preview: Testcross to Determine an Unknown Genotype • A testcross is a mating between - An individual of unknown genotype and… -A homozygous recessive individual what is a testcross: cross one unknown genotype with a recessive (pp). How come it is powerful? Helps you determine the genotype of the purple flower. Testcross: Genotypes P_ pp Two possibilities for the purple flower: PP Gametes P P Offspring Pp Pp All purple P p Pp p pp 1 purple : 1 white A single-gene model explains Mendel’s ratios Figure 2-12 part 15 Summary • A particular trait (phenotype) is determined by a factor (Gene). • There are two forms of this factor (alleles). • Principle of dominance: When T and t co-exist in a plant, one observes the T phenotype. T: dominant t: recessive • Principle of segregation: The two alleles, T and t, separate (segregate) during gamete formation, then unite at random, one from each parent, at fertilization. Secrets of Mendel’s Success • Limited the number of variables simplified the problem • Started with pure breeding parents • Quantified results just counted the number, came up with a ratio, tested his hypothesis • Developed possible models that could be tested Complications when extended to human populations •  Most traits are affected by more than one gene and cannot be analyzed using simple Mendelian genetics •  Many single gene traits that can be followed cause rare diseases, rather than common phenotypes •  Genetics is not straight forward: – No pure breeding humans – Generation time is long – No controlled matings – Siblings rarely mate to generate F2 Lecture 2: 4/4/13 III. The rules of probability-part I • Probability = # times event is expected to happen # opportunities (trials) so example you roll a die, what is the chances you get a six? 1/6 because when you roll a dice, there are 6 opportunities and one of them (the one you want) Product Rule: The probability of independent events occurring together is the product of the probabilities of the individual events. Probability of (A and B) is P(AB) = P(A) X P(B) works when the event is independent. For example, when women are pregnant the first time, what are the chances she'll have a girl? 1/2. Second pregnancy, with the first one having been a boy, what are the chances she'll have a girl? 1/2 b/c the pregnancy between the first and second are independent from one another. Women have two children, what are hte chances it is 2 girls? (1/2) x (1/2) = 1/4 Probability • What is the probability of drawing an Ace of Hearts from this deck of cards? it requires an Ace and a heart. Apply product rule. Chances of getting an Ace = 4/52 or 1/13. Chances of getting a heart 1/4 or 13/52. - So (4/52) x (1/4) = 1/52. Sum Rule: General Sum Rule: P [A or B] = P [A] + P [B] - P[A and B] Can be applied towards ind and dep events If A and B are independent events, the probability that A or B occurs, P(A or B) is P[A + B] = P(A) + P(B) - [P(A) X P(B)] Probability • What is the probability of drawing an Ace or a Heart from this deck of cards? 1/13 for an Ace and 1/4 for a heart. (1/13) [Chances it is an Ace] + (1/4) [Ch...
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