1. Probability and Punnett Square

2. Probability:
likelihood that a specific event
will occur.
Principle of probability:
used to predict the outcomes of
genetic crosses.

3. Two important points to remember with
probabilities:
Past outcomes do not affect future events
Probabilities predict the average outcome of many events

4. Punnett Squares:
diagrams that model genetic crosses.
can be used to predict and compare
the genetic variations that will result
from a cross.

5. Homozygous:
Organisms that have two identical
alleles for a particular trait—TT,tt
Heterozygous:
Organisms that have two different
alleles for the same trait--Tt

6. Monohybrid Crosses STEP  STEP  STEP  STEP 
Cross two Alaskan huskies that are heterozygous for brown eyes (Bb).
STEP 
BB = brown eyes Bb = brown eyes bb = blue eyes B b
female gametes
Genotypes %
25% BB, 50% Bb, 25% bb
Ratios
1BB:2Bb:1bb
STEP  B b
male gametes BB Bb
Cross
Bb x Bb
STEP 
STEP  Bb bb
Phenotypes %
75% Brown eyed, 25% Blue eyed
Ratio
3 Brown eyed: 1 Blue eyed

7. DIHYBRID CROSSES (R r) (Gg) F.O.I.L First Outer Inner Last RG Rg rG rg
Cross: RrGg X RrGg
EXTRA STEP - Finding the possible gametes
STEP  rG rg
(R r) (Gg)
F.O.I.L
First
Outer
Inner
Last RG Rg

8. Incomplete Dominance
In incomplete dominance, neither allele is Dominant-blending of traits when two different alleles for the same trait occur together.
Colors blend together
heterozygous individuals = rd phenotype
red
pink
white

9. Incomplete Dominance Four O’ Clocks, if you
cross a red RR (which is always pure)
with a white WW
(that is also always pure) , you get a pink RW (which is always hybrid / heterozygous RW RW RW RW

10. Incomplete Dominance
In another flower, if red RR and blue BB flowers are crossed, they produce a 3rd purple RB flower
What would be the genotype ratio and phenotype ratio if you crossed two purple flowers?

11. Cross of two purple flowers RB X RB What are gamete possibilities?
genotype ratio
phenotype ratio
Can you have a heterozygous red or hybrid blue flower? R B RR RB R
red
purple BB RB B
purple
blue

12. Codominance
Both alleles contribute to the phenotype of the organism by showing up simultaneously (at the same time) in heterozygous individuals.
In cattle and horses, if you cross a pure red (RR) with a pure white (WW), you get (RW) which produces the color roan.

13. Codominance
These cattle or horses actually have both red and white hairs intermixed, or are spotted. Roan is a third phenotype.
If you cross a roan with a white… R W RW WW W
roan
white RW WW W
roan
white

14. Codominance Andalusian chickens also show this pattern of inheritance.
If you cross a black (BB) chicken
With a white (WW) chicken
You get black+white speckled (BW) chicken