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### Dihybrid Crosses

### Now you try!Zork worksheet due at the end of class

Student Expectation (SE) 6F - predictpossible outcomes of various genetic combinations such as monohybrid crosses, dihybrid crosses and non-Mendelian inheritance

Two heterozygous red-flowering plants are crossed. If red is dominant over white, what is the most likely phenotype in the offspring?

Rr

Rr

R

r

R

RR

Rr

Red

r

Rr

rr

1. Dihybrid Crosses

- A dihybrid cross is a prediction of an offsprings genotype for two traits such as:
- Yellow seeds and wrinkled seeds
- Blond hair and blue eyes
- Purple lipped and one legged

2. Show how the gametes form from a cross between Round,yellow seeds (RRYY) and Wrinkled, green seeds (rryy)

RRYY

rryy

2n

Meiosis 1

2n

rryy

rryy

RRYY

RRYY

Meiosis 2

RY

RY

RY

RY

ry

ry

ry

ry

n

- 3. Show how the gametes form from a cross between two offspring from the F1 generation

RrYy

RrYy

2n

Meiosis 1

2n

RrYy

RrYy

RrYy

RrYy

Meiosis 2

RY

ry

Ry

rY

RY

ry

Ry

rY

n

Round/green = ?

wrinkled/Yellow = ?

wrinkled/green = ?

RY

ry

Ry

rY

RY

ry

Ry

rY

4. DihybridCross5. DihybridCross Short Cut

Muppets can either have Ruffled feathers (R) or smooth feathers (r). They can also have Yellow eyes (Y) or green eyes (y)

Big Bird and Mrs. Bird are heterozygous for ruffled feathers and yellow eyes. What are the chances their offspring will have smooth feathers and Yellow eyes?

Dihybrid Cross

Step 1) figure out what this means:

Big Bird and Mrs. Bird are heterozygous for ruffled feathers and yellow eyes

Heterozygous: different

That means Mr. and Mrs. Bird are both:

RrYy

Find the chances of having one trait…

- What are the chances the baby will have smooth feathers?

Rr

Rr

R

r

R

RR

Rr

¼ chance of smooth feathers

r

Rr

rr

Find the chances of having one trait…

- What are the chances the baby will have yellow eyes?

Yy

Yy

Y

y

Y

YY

Yy

¾ Chance of yellow eyes

y

Yy

yy

Step 3

- There is a 3/16 chance the baby will have smooth feathers and yellow eyes.

Chances of smooth feathers

Chances of yellow eyes

Chances of smooth feathers AND yellow eyes

=

x

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