1. Dihybrid Crosses
Unit 4 – Lecture 6

2. Dihybrid Cross a 4x4 representation of crossing TWO traits
monohybrid = 1 trait w/ 2 alleles
= 1 allele gamete each for 2x2 box
dihybrid = 2 traits w/ 2 alleles EACH = 4 alleles
= 2 allele gametes each for 4x4 box
[one allele for each trait in each gamete]

3. Solving a Dihybrid Determine the genotypes of each parent
Given to you, or you have to solve for them
Given: Parent #1 AABB
Given: Parent #2 aabb

4. Solving a Dihybrid
Create your dihybrid cross [4x4]

5. Solving a Dihybrid Determine Gametes:
pair first allele of first trait with first allele of second trait
A A B B
first gamete = AB

6. Solving a Dihybrid Determine Gametes:
pair first allele of first trait with second allele of second trait
A A B B
second gamete = AB

7. Solving a Dihybrid Determine Gametes:
pair second allele of first trait with first allele of second trait
A A B B
third gamete = AB

8. Solving a Dihybrid Determine Gametes:
pair second allele of first trait with second allele of second trait
A A B B
fourth gamete = AB

9. Solving a Dihybrid Determine Gametes:
pair first allele of first trait with first allele of second trait
a a b b
first gamete = ab

10. Solving a Dihybrid Determine Gametes:
pair first allele of first trait with second allele of second trait
a a b b
second gamete = ab

11. Solving a Dihybrid Determine Gametes:
pair second allele of first trait with first allele of second trait
a a b b
third gamete = ab

12. Solving a Dihybrid Determine Gametes:
pair second allele of first trait with second allele of second trait
a a b b
fourth gamete = ab

13. Solving a Dihybrid
Label cross w/ parent gametes above / to left AB ab

14. Solving a Dihybrid Fill in boxes:
fill DOWN each column w/ whatever’s there AB ab AB ab
A B

15. Solving a Dihybrid Fill in boxes:
fill ACROSS each column with whatever’s there AB ab
A B AB ab
AaBb

16. Solving a Dihybrid Determine Genotype Ratios
record all genotypes you have
count and record number of each genotype
AaBb: 16/16 [or 100%] AB ab
AaBb

17. Solving a Dihybrid Determine Phenotype Ratios
count how many of each phenotype you have
record # of phenotypes represented
purple, round: 16/16 [or 100%] AB ab
AaBb

18. Solving a Dihybrid #2 Determine the genotypes of each parent
Given to you, or you have to solve for them
Given – both parents are heterozygous for both traits.
Given: Parent #1 QqRr
Given: Parent #2 QqRr

19. Solving a Dihybrid
Create your dihybrid cross [4x4]

20. Solving a Dihybrid Determine Gametes:
pair first allele of first trait with first allele of second trait
Q q R r
first gamete = QR

21. Solving a Dihybrid Determine Gametes:
pair first allele of first trait with second allele of second trait
Q q R r
second gamete = Qr

22. Solving a Dihybrid Determine Gametes:
pair second allele of first trait with first allele of second trait
Q q R r
third gamete = qR

23. Solving a Dihybrid Determine Gametes:
pair second allele of first trait with second allele of second trait
Q q R r
fourth gamete = qr

24. Solving a Dihybrid Label cross w/ parent gametes above / to left QR Qr

25. Solving a Dihybrid Fill in boxes: Q R Q r q r
fill DOWN each column w/ whatever’s there QR Qr qR qr
Q R
Q r
q r

26. Solving a Dihybrid Fill in boxes: QQRR QQRr QqRR QqRr QQrr Qqrr qqRR
fill ACROSS each column with whatever’s there QR Qr qR qr
QQRR
QQRr
QqRR
QqRr
QQrr
Qqrr
qqRR
qqRr
qqrr QR Qr qR qr
Q R
Q r
q r

27. Solving a Dihybrid Determine Genotype Ratios
record all genotypes you have
count and record number of each genotype
[not going to make you do it for this one.. just know how to] QR Qr qR qr
QQRR
QQRr
QqRR
QqRr
QQrr
Qqrr
qqRR
qqRr
qqrr

28. Solving a Dihybrid Determine Phenotype Ratios
count how many of each phenotype you have
record # of phenotypes represented
9/16 - purple, round
3/16 - purple, wrinkled
3/16 - white, round
1/16 - white, wrinkled QR Qr qR qr
QQRR
QQRr
QqRR
QqRr
QQrr
Qqrr
qqRR
qqRr
qqrr