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 singlegene model explains Mendel’s ratios Figure 212 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 coexist 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 probabilitypart 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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 Spring '08
 Ribaya
 Zygosity

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