Chapter 14.
https://www.youtube.com/watch?v=y4Ne9DXk_Jc


Mendel ’ s laws:

Segregation

Dominance

Independent Assortment reflect same laws of probability that apply to tossing coins or rolling dice


Calculating probability of making a specific gamete is just like calculating the probability in flipping a coin
 probability of tossing heads? 50% or 1/2
 probability making a P gamete…
Hh
PP
H
50% h
P
100%
P


Outcome of 1 toss has no impact on the outcome of the next toss = independent events
 probability of tossing heads each time?
50%
 probability making a P gamete each time?
50%
Pp
P p

Pp x Pp sperm egg
P P
1/2 x 1/2 = offspring
PP
1/4 male / sperm
P p
P p
PP
Pp
Pp pp
Chance that an event can occur in 2 or more different ways =
Rule of Addition
P p
1/2 x 1/2 = p P
1/2 x 1/2 = p p
1/2 x 1/2 =
+
Pp
1/4
1/4
1/2 pp
1/4


Chance that 2 or more independent events will occur together
 probability that 2 coins tossed at the same time will land heads up
1/2 x 1/2 = 1/4
 probability of Pp x Pp
 pp
1/2 x 1/2 = 1/4


Rule of multiplication also applies to dihybrid crosses
 heterozygous parents — YyRr
 probability of producing a yyrr offspring?
 probability of producing y gamete =
 probability of producing r gamete =
 probability of producing yr gamete =
1/2
1/2
1/2 x 1/2 = 1/4 ie. An ovum
 probability of producing a yyrr offspring =
1/4 x 1/4 = 1/16 ie. An ovum & a sperm

Rule of addition to determine the chances of heterozygous possibilities

Chance that an event can occur
2 or more different ways
 sum of the separate probabilities
 probability of Pp x Pp

Pp sperm egg
P p
1/2 x 1/2 = offspring
P p
1/4 p P
1/2 x 1/2 = p P
1/4
1/4
+ 1/4
1/2

Independent events in sequence
X
1/2 x 1/2 x 1/2 x 1/2 =
AND
(and then)

Mutually exclusive events
+
1/2 + 1/2 + 1/2 + 1/2 =
OR

Probability Examples
1. What are the chances of having 4 boys and then a girl?
2. A couple has 2 children, both girls. If the woman gives birth to a third child, what is the probability that the third child will be a boy?
3. What ’ s the probability that the genotype Bb will be produced from parents Bb x Bb?
4. What ’ s the probability that the genotype ttgg will be produced by parents TtGg x TtGg?
5. What ’ s the probability that the genotype Aa will be produced by parents aa x Aa?

Probability Examples
6. A student has a penny, nickel, dime, and a quarter. She flips them all simultaneously and checks for heads or tails. What is the probability that all four coins will come up heads? She flips all four coins again. What is the probability she well get four heads both times?
What probability rule did you use to determine this?
7. Using Hardy-Weinberg’s Equation of Equilibrium: p 2 + 2pq + q 2
What is the probability of expressing the dominant phenotype?
8. What is the chance that a child will carry the HbS gene but not have sickle cell disease?
9. What are the chances that two heterozygous parents for sickle cell will have three children who are homozygous for normal RBS’s?
10. Assume a germ cell has HhEe , where h and e are each on a single gene and the genes are not linked. What is the probability of a gamete having he ?
What is the probability of having a blond(e) hair, blue-eyed baby if both parents are dihybrids?


Test to see if your data supports your hypothesis

Compare “ observed ” vs. “ expected ” data
 is variance from expected due to “ random chance ” ?
 is there another factor influencing data?


 degrees of freedom (df) = # of classes -1 = (n-1) statistical significance - unlikely to have occurred by chance null hypothesis - one you can accept or reject based on probability
X 2 = ∑ (Observed Value - Expected Value)
Expected Value
2