1. DIHYBRID CROSSES We’re still thinking MENDELIAN genetics
(2 possible phenotypes)
(Upper case and lower case letters)

2. How many different genotypes can you get when you cross a wrinkled seed pea plant with a smooth seed pea plant? (W=wrinkled, w=smooth)

3. How many different genotypes can you get when you cross a green seeded pea plant with a yellow seeded pea plant?
Does it matter if they’re wrinkled or smooth?

4. (W=wrinkled, w=smooth) (G=green seed, g=yellow seed) What if you cross a wrinkled, green seeded plant with a smooth yellow seeded plant?

5. Mendel’s Law of Independent Assortment says…
Two (or more) traits on different chromosomes are inherited independently of each other
That means the offspring can be green or yellow, wrinkled or round

6. What are the possible gamete combinations we could have with 2 heterozygous parents?
GgWw GgWw ? ?

7. Use the FOIL method to find gametes! (write this in your handout)
F – First allele of each trait
O – Outside of both traits
I – Inside of both traits
L – Last allele of each trait
GgWw
GW Gw gW gw

8. Practice setting up the crosses for number 2
Mendel’s Law of Independent Assortment states that gene pairs separate independently of each other. That means two traits don’t have to be inherited together.
Practice setting up the crosses for number 2
R R D D R r d d
R r D D r r d d
r r D d R r D d

9. Plugging it into a Punnett Square:RD Rd rD rd

10. Tips for filling in a dihybrid cross
Always keep the traits in the same order
Keep letters from the same trait together
Write dominant letter first… ONLY IF YOU CAN
Try #3

11. Check your work on #3 P RD Rd rD rd
RRDD
RRDd
RrDD
RrDd
RRdd
Rrdd
rrDD
rrDd
rrdd
Red with Diamonds White with Diamonds Red without diamonds White without diamonds

12. Practice on your puppy sheet:
Two parents are heterozygous for floppy ears and long hair: F f H h
Find the gametes

13. Practice on your Puppy Genetics sheet: Show the cross for two parents that are heterozygous for floppy ears and long hair
F = floppy ear H = long hair
f = pointy ear h = short hair
Cross
_______ _______
___ ___ ___ ___ ___ ___ ___ ___ P

14. ___ ___ ___ ___ ___ ___ ___ ___
More practice
Cross
_______ _______
___ ___ ___ ___ ___ ___ ___ ___ P

15. Polygenic Traits – pg 216 Same setup – different phenotypes
Cross
_______ _______
___ ___ ___ ___ ___ ___ ___ ___
Really short
Short
Medium
Tall
Really Tall