Journal:1) Suppose you guessed on a

multiple choice question (4 answers). What was the chance that you marked the correct answer? Explain.

2) What is the chance (in %) to randomly choose a student in this class that would be a girl?A boy? Explain

We study genetics in order to:A. Understand how existing

individuals developed. B. To make predictions

regarding the next, yet unborn generations.

For this we need to understand

Principles of Probability and Ratio

Principles of Probability

Probability – the likelihood that a particular event will occur, expressed in percentage.

It predicts the estimated, average number, not the exact number of occurrences.

Ratio: The proportion between specific outcomes. Divide the probabilities by the smallest one: Consider two possible occurrences: * If there is a 75% chance for one, and 25% for the other, then the ratio between them is: 75:25 = 3:1 ratio* If there is 50% chance for both:50:50 = 1:1 ratio.

1) Probability = Number of selected events

Number of all possible events

For example: The chances for a coin to fall on heads is:No. of selected events

No. of all possible events=

1

2=50%

The chances for a dice to fall on an even number is:

=3

6=50%

The chances for two coins to land on heads:

=1

4= 25%

2) Probability of two (or more) independent events is the product of their individual probabilities:The chances for two coins to land on heads:

= = 25%1

4X =

1

2

1

2X

Three coins to land on heads: ?

A. Calculate the chances to get the following occurrences:

1) Coin lands on heads twice in a row (HH).

2) Two coins landing on same side (T or H) twice.

3) At least one of the two coins lands on heads.

4) First coin-heads, second coin- any.

C. Compare: Calculated vs. Measured

H:

HH:

Same side twice:At least one H:

Calc. Measured50% 20 =

50 =

B. Try it with coins!

Copy the following data table:

H T

Tally (20 throws):

HH TTHT TH

Tally (50 throws):

One coin:

Two Coins:

Throw the coins and count!

D. In Conclusion:

1) Did you get the exact numbers you predicted by calculations? Describe.

2) Were the calculations any close to the actual result?

3) What can be done in an experiment to get closer to the predicted probability?