DIHYBRID CROSSES

We’re still thinking MENDELIAN genetics– (2 possible phenotypes)

– (Upper case and lower case letters)

• 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)

• 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?

(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?

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

What are the possible gamete combinations we could have with 2

heterozygous parents?GgWw GgWw

? ?

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

Practice!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

Plugging it into a Punnett Square:

P RD Rd rD rd

RD

Rd

rD

rd

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

Check your work on #3

Red with Diamonds

White with Diamonds

Red without diamonds

White without diamonds

P RD Rd rD rd

RD RRDD RRDd RrDD RrDd

Rd RRDd RRdd RrDd Rrdd

rD RrDD RrDd rrDD rrDd

rd RrDd Rrdd rrDd rrdd

Practice on your puppy sheet:

Two parents are heterozygous for floppy

ears and long hair: F f H hFind the gametes

Practice on your Puppy Genetics sheet: Show the cross for two parents that are

heterozygous for floppy ears and long hair

PCross

_______ _______

___ ___ ___ ___ ___ ___ ___ ___

F = floppy ear H = long hairf = pointy ear h = short hair

More practice

PCross

_______ _______

___ ___ ___ ___ ___ ___ ___ ___

Polygenic Traits – pg 216Same setup – different phenotypes

PCross

_______ _______

___ ___ ___ ___ ___ ___ ___ ___

Really short

Short Medium Tall Really Tall