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Lecture 18

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Illinois State University

Biological Sciences

BSC 219

mortimer

Spring

Description

Probabilities
Probability
Probability: how likely an outcome is to occur
Quantified as a number 0 to 1
Higher the probability the more likely the outcome
Product Law: probability of independent events occurring together is the product of the
probabilities of the individual events
Used to determine the probability of two or more independent events occurring
Seen as AND so smaller number
Sum Law: states the probability of either of two mutually exclusive events occurring is the sum
of their individual probabilities
Used to determine the probability of two or more mutually exclusive events occurring
Seen as OR so bigger number
Binomial Shortcut
Seen as an equation
N= total number of events (ex: kids)
S= number of times outcome 1 occurs
T= number of times outcome 2 occurs
A= probability of outcome 1 (ex: a boy)
B= probability of outcome 2 (ex: a girl)
Factorial Review
0! = 1 1! = 1 2! = 2 3! = 6 4!= 24 5! = 120
Example: What is the probability that a couple will have 2 boys and 2 girls?
N= 4 kids
S= 2 boys
T= 2 girls
A= ½
B= ½
Different Modes of Inheritance
Mode of Inheritance: manner in which a particular genetic trait is transmitted from one
generation to the next
Autosomal dominant, Autosomal recessive, X-linked dominant, X-linked recessive,
Cytoplasmic, Imprinting
Different modes in a Dihybrid Cross Expect unusual ratios when examining different traits with different modes of
inheritance
Normally, a dihybrid cross results in a 9:3:3:1 ratio
Example: Blood groups and albinism
Use the product law for example: albino and blood type A
¼ chance of being albino
¼ chance of blood type A
overall chance: 1/16
Significance
1. First propose a hypothesis
We shrank since the spider is the same size as us
2. An experiment is then performed to determine if the hypothesized results are observed
(deviation from the hypothetical results is expected due to chance)
We measure the spider (height, weight, body length, leg length)
3. Observations are made and the deviation is measured
The spider weighs .5 lbs and the average spider weighs .3 lbs
4. We then use a method to determine if the a

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