Name ________________________________________ Date _______ Pd ____
Analyzing Inheritance –Genetics has predictive value.
Probability – the chance that a given event will occur.
 Probability = the number of times a particular event occurs/ the number
of opportunities for the event to occur (the number of trials).
o Ex: A coin has 2 sides. A head is on one of the sides. The probability
of flipping heads is 1 out of 2 or ½.
 Each event is completely independent of the results of every previous
event.
o Ex: You toss a coin 3 times in a row and each time it comes up heads.
What is the probability it will come up heads on the 4th toss? It is still
½.
 To determine the probability of an event happening numerous times in a
row, you multiply the individual events.
o Ex: what are the chances of having 3 girls in a row? ½ x ½ x ½ =
1/8.
Probability and Genetics
Probability applies to genetics because the formation of gametes depends
on random events.
o 2 alleles – 1 in 2 chance of a gamete getting one of the alleles or ½.
3 Rules of Probability
1. As you increase the number of events, you will decrease
the deviation and get closer to the expected results.
2. Previous events do not affect future outcomes.
3. The probability of independent events occurring at the
same time is the product of their individual probabilities.
This is the product rule.