Probability & Genetics

Genetics & Probability

Mendel’s laws:segregation independent assortment

reflect same laws of probability that apply to tossing coins or rolling dice

Probability & genetics

Calculating probability of making a specific gamete is just like calculating the probability in flipping a coinprobability of tossing heads? probability making a B

gamete?50%

100%BBB

B

BbB

b

Probability & genetics

Outcome of 1 toss has no impact on the outcome of the next tossprobability of tossing heads each

time?probability making a B gamete each

time?

50%

50%Bb

B

b

Calculating probabilitysperm egg

1/2 1/2

offspring

=x 1/4P P PP

P p Pp

1/2 1/2 =x 1/4p p pp

p P

Pp x Pp

P pmale / sperm

P

pfemal

e / e

ggs

PP Pp

Pp pp

1/2 1/2 =x 1/4

1/2 1/2 =x 1/41/2

+

Chance that 2 or more independent events will occur togetherprobability that 2 coins tossed at the

same time will land heads up

probability of Pp x Pp pp

Rule of multiplication

1/2 x 1/2 = 1/4

1/2 x 1/2 = 1/4Pp

P

p

Calculating probability in crossesUse rule of multiplication to predict crosses

YyRr YyRrx

yyrr

?%

Yy Yyx Rr Rrx

1/4 1/4

1/16yy rr

x

Apply the Rule of Multiplication

Got it?Try this!

AABbccDdEEFf AaBbccDdeeFfx

AabbccDdEeFF

Bb x Bb bbcc x cc ccDd x Dd DdEE x ee EeFf x Ff FF

AA x Aa Aa 1/21/4

11/2

11/4 1/64

Rule of addition Chance that an event can occur

2 or more different ways sum of the separate probabilitiesprobability of Bb x Bb Bb

sperm egg offspring

1/2 1/2 =x 1/4B b Bb

1/2 1/2 =x 1/4b B Bb

1/41/4+

1/2