1. Did you do your homework?
Happy Monday Bio-Ninjas! Please READ ALL sections below!
Journals: NO NEW NOTES TODAY!!!
Table of Contents
Right Page 45:
Dihybrid Crosses
Left Page 44
Dihybrid Practice
EQ: How are genetic outcomes predicted and when two traits are involved?
Due today:
Alien Punnett Square Homework
One Day Late: (70)
Two days Late: (50)
Three Days Late: (0)
Did you do your homework?
HAVE ALL HOMEWORK, LATE WORK/EXTRA CREDIT OUT READY TO BE CHECKED!

2. Homework Check…Aliens!

3. What are the trait(s)?

4. What are the traits?

5. What are the traits?

6. Dihybrid Cross: a cross that shows the possible offspring for two traits
Fur Color: B: Black b: White
Coat Texture: R: Rough r: Smooth
In this example, we will cross two individuals that are both heterozygous for each trait. What will their genotypes be?
BbRr x BbRr

7. BbRr heterozygous for both traits.
Notice how the genotypes are written when working with dihybrid scenarios…
BbRr heterozygous for both traits.
FFTt Homozygous dominant for trait 1
heterozygous for trait 2
rrXx Homozygous recessive for trait 1
hhgg Homozygous recessive for both traits

8. How do you set up a dihybrid cross?
Before setting up a dihybrid cross/Punnett square one must understand the following concept…
The Principle of Independent Assortment: the separation and assortment of genes during meiosis is independently random and gives traits equal opportunity of appearing together.
*Remember “shuffling the deck”

9. Dihybrid Crosses…the steps
BbRr x BbRr
Step 1: Find ALL possible gamete combinations that can be made from each parent’s genotype.
Remember, each parent gives one allele for each trait so each gamete must have one “B” allele and one “R” allele.
Parent 1
Parent 2
You will ONLY use the following steps if you are ever asked to “find the possible gametes”
-more than likely on a handout
-rarely on a test but you will still need to know just in case.

10. BbRr x BbRr F O I L BR Br bR br Possible combinations: Parent 2
Step 2: FOIL Method
Combine the FIRST, OUTER, INNER, and LAST letters of the genotype.

11. Each allele from trait 1 must “dance” with each allele from trait 2

12. Remember…you will only use FOIL if you are asked to “find the possible gametes” Also, you will more than likely never have to fill out an entire dihybrid Punnett Square but you will definitely need to recognize and know how to read one.

13. Step three: Set up the Punnett square using the gametes (possible genotypes) from each parent.BR bR br Br
BBRR
BbRR
BbRr
BBRr
BBrr
Bbrr
bbRR
bbRr
bbrr

14. Dihybrid Crosses: a cross that shows the possible offspring for two traits
BBRR
BbRR
BbRr
BBRr
BBrr
Bbrr
bbRR
bbRr
bbrr
BbRr x BbRr
Fur Color: B: Black b: White
Coat Texture: R: Rough r: Smooth
Glue this into your journals!

15. Phenotypic Ratio= 9:3:3:1 BR bR br Br
BBRR
BbRR
BbRr
BBRr
BBrr
Bbrr
bbRR
bbRr
bbrr
How many of the offspring would have black, rough coat?
How many of the offspring would have a black, smooth coat?
How many of the offspring would have a white, rough coat?
How many of the offspring would have a white, smooth coat?
Phenotypic Ratio=
9:3:3:1
Fur Color: B: Black b: White
Coat Texture: R: Rough r: Smooth
Write down and answer these questions on the left side under what you glued in.

16. SAVE YOURSELF SOME TIME!!
When crossing two individuals that are heterozygous for both traits on a dihybrid cross, the phenotypic ratio will ALWAYS be 9:3:3:1

17. Is the FOIL method the only way to solve dihybrid probabilities?

18. Fractions Method BbRr x BbRr Bb Bb Rr Rr
To figure out probabilities of dihybrid crosses we will use the “fractions method” for multiple reasons:
It’s faster
You’re doing what you already know
You’ll get the same answer!
You don’t have to FOIL
You don’t have to fill in a 16 box square
Umm…it’s faster
Step 1: Match up the alleles for both individuals
Parent 1
Parent 2
BbRr x BbRr Bb Bb Rr Rr

19. Step 2: Create a Monohybrid Punnett square for each of the traits
Parent 1
Parent 1 B b R r B BB Bb R RR Rr b Bb r Rr rr bb
Parent 2
Parent 2
Step 3: Fill in the punnett squares for each trait

20. Step 4: Find the probability for each trait then multiply
Parent 1
Parent 1
Fur Color: B: Black b: White B b R r B
Coat Texture: R: Rough r: Smooth BB Bb R RR Rr b Bb Rr rr bb r
Parent 2
Parent 2
How many of the offspring would have a black, rough coat? 3 3 9 X = 4 4 16

21. Step 4: Solve probabilities by multiplying fractions
Parent 1
Parent 1
Fur Color: B: Black b: White B b R r B
Coat Texture: R: Rough r: Smooth BB Bb R RR Rr b Bb Rr rr bb r
Parent 2
Parent 2
How many of the offspring would have a black, smooth coat? 3 1 3 X = 4 4 16

22. Step 4: Solve problems by multiplying fractions
Parent 1
Fur Color: B: Black b: White
Parent 1 B b R r
Coat Texture: R: Rough r: Smooth B BB Bb R RR Rr b Bb Rr rr bb r
Parent 2
Parent 2
How many of the offspring would have a white, rough coat? 1 3 3 X = 4 4 16

23. Step 4: Solve problems by multiplying fractions
Parent 1
Parent 1
Fur Color: B: Black b: White B b R r B
Coat Texture: R: Rough r: Smooth BB Bb R RR Rr b Bb Rr rr bb r
Parent 2
Parent 2
How many of the offspring would have a white, smooth coat? 1 1 1 X = 4 4 16

24. Practice in your notes…
In pea plants, yellow seeds (Y) are dominant over green seeds (y), and rounded peas (R) are dominant over wrinkled peas (r).
Cross a plant that is heterozygous for both traits with a plant that is homozygous recessive for both traits.
Genotypes:
YyRr and yyrr
What is the probability that the plant will be yellow and wrinkled?

25. FOIL (dance) the parents…
YyRr and yyrr

26. Isolate the genotypes for trait 1 and trait 2
YyRr and yyrr
Parent 1: Yy Rr
Parent 2: yy rr
Yy x yy
Rr x rr

27. Y y R r y Yy yy r Rr rr y Yy Rr rr yy r 2 2 4 X = 4 4 16
How many of the offspring would have a yellow, wrinkled seed? 2 2 4 X = 4 4 16

28. YyRr X yyrr YR yR yr Yr
YyRr
yyRr
yyrr
Yyrr 4 1 or 16 4

29. 1. *Hybrid*
2. *Purebred*
What is the probability that the baby Reebop will have 2 antennae and 3 body segments?

30. A a B b A AA Aa b Bb bb AA Aa A b Bb bb 4 2 8 = X 4 4 16
What is the probability that the baby Reebop will have 2 antennae and 3 body segments?
1. *Hybrid*
2.*Purebred* A a B b A AA Aa b Bb bb AA Aa A b Bb bb 4 2 8 = X 4 4 16

31. Genotype / phenotype code
1. *Hybrid*
2. Hybrid eyes
Characteristic
Genotype / phenotype code
eyes
EE = 2 eyes
Ee = 2 eyes
ee = one eye
humps
HH = 1 hump
Hh = 1 hump
hh = 3 humps
What is the probability that the baby Reebop will have 2 eyes and 3 humps?

32. Genotype / phenotype code
Characteristic
Genotype / phenotype code
eyes
EE = 2 eyes
Ee = 2 eyes
ee = one eye
humps
HH = 1 hump
Hh = 1 hump
hh = 3 humps
What is the probability that the baby Reebop will have 2 eyes and 3 humps?
1. *Hybrid*
2.hybrid eyes E e H h E EE Ee h Hh hh Ee ee e h Hh hh 3 2 6 = X 4 4 16

33. Genotype / phenotype code
Characteristic
Genotype / phenotype code
eyes
EE = 2 eyes
Ee = 2 eyes
ee = one eye
humps
HH = 1 hump
Hh = 1 hump
hh = 3 humps
What would the phenotypic ratio be? E e H h
1. *Hybrid*
2.hybrid eyes EE E Ee h Hh hh
2 eyes, 1 hump:
2 eyes, 3 humps:
1 eye, 1 hump:
1 eye, 3 humps:
¾ x ¾ = 9/16 Ee ee e h Hh hh
¾ x 2/4 = 6/16
¼ x 2/4 = 2/16
9:6:2:2
¼ x 2/4 = 2/16

34. Work on your Dihybrid practice for the rest of class
Work on your Dihybrid practice for the rest of class. We’ll finish tomorrow 

35.  HAPPY TUESDAY  On the left side of your pedigree notes:
Bellwork:
On the left side of your pedigree notes:
Sketch the pedigree chart Determine the genotypes for numbers 1-5 using the information given.
 HAPPY TUESDAY  5 Tt tt tt Tt
Shaded = Tongue Rolling
Not Shaded = Non Tongue Rolling
Tongue Rolling (T) is Dominant to Non Tongue Rolling (t)
Bonus: Is there anything particularly interesting about this family?
Have your Pedigree Homework and any Late Work out on your desk! tt

36. Punnett Square Homework (FC)
Due This Week:
Tuesday:
Pedigree HW (FC)
Family Tree (FC)
Punnett Square HW (70)
Wednesday:
Pedigree HW (70)
Family Tree (70)
Punnett Square HW (50)
Thursday:
Pedigree HW (50)
Family Tree (50)
Friday:
Notecards (picture w/color)
Have out:
Pedigree Homework
Due today:
Turn in or show me
Graded Quiz
Family Tree Part 1
Notecards (50)
Punnett Square Homework (FC)
I have PLENTY of extra Punnett Square EXTRA CREDIT if you need or want it. 
Extra Credit can be turned in all the way up until the day of the test.

37. Pedigree HW check

38. Case Study #1 -2 points each shape A = Normal -2 points each genotype
a = albinism Aa Aa aa Aa A- A- Aa Aa Aa aa

39. H = Huntington's Disease
-2 points each shape
-2 points each genotype
Case Study #2
H = Huntington's Disease
h = Normal hh Hh hh hh hh hh hh H- Hh hh hh hh hh hh Hh

40. Heterozygous Case Study #3 Nn No -2 points each genotype
N = Neurofibromatosis
n = Normal
-2 points each Nn nn
-2 points each genotype nn nn Nn nn Nn Nn Nn nn nn nn nn N- N- nn