Genetics - Dihybrid crosses

GENETICS D I H Y B R I D C R O S S E S: predicting 2 traits at a time Robert Perry MALIBU HIGH SCHOOL

Gregor Mendel studied 7 characteristics of garden peas.

Let’s see how to predict crosses with TWO traits at a time:

1. Choose symbols:

1. Choose symbols: SEED SHAPE

RR = round Rr = round r r = wrinkled

1. Choose symbols: SEED SHAPE

SEED COLOR

RR = round Rr = round r r = wrinkled YY = yellow Yy = yellow y y = green

1. Choose symbols: SEED SHAPE

SEED COLOR

RR = round Rr = round r r = wrinkled YY = yellow Yy = yellow y y = green

RECALL THAT ROUND & YELLOW ARE BOTH DOMINANT TRAITS.

WE WILL WORK A DIHYBRID CROSS BETWEEN 2 ROUND & YELLOW HYBRID PEAS.

Rr Yy (BOTH PARENTS WILL HAVE THE SAME GENOTYPE IN THIS PROBLEM)

2. Write gamete genotypes using Mendel’s Principle of Independent Assortment: Parental Rr Yy

genotype (both parents)

2. Write gamete genotypes using Mendel’s Principle of Independent Assortment: Parental Rr Yy

genotype

RY possible Gamete genes

2. Write gamete genotypes using Mendel’s Principle of Independent Assortment: Parental Rr Yy

RY

genotype

Ry possible Gamete genes

2. Write gamete genotypes using Mendel’s Principle of Independent Assortment: Parental Rr Yy

RY

Ry

genotype

rY possible Gamete genes

2. Write gamete genotypes using Mendel’s Principle of Independent Assortment: Parental Rr Yy

RY

Ry

rY

genotype

ry possible Gamete genes

2. Write gamete genotypes using Mendel’s Principle of Independent Assortment: Parental Rr Yy

genotype

RY

Ry

rY

ry

1/4

1/4

1/4

1/4

Gametes

Notice there are now FOUR different genetic possibilities for a gamete

3. Make a 16 square Punnett Square: Rr Yy RY

male genotype and gametes

RY Rr Yy

Ry rY ry

Ry

female genotype and gametes

rY

ry

4. Match up genes from both parents: Rr Yy RY

Rr Yy

Ry

rY

ry

RY

RRYY RRYy

RrYY

RrYy

Ry

RRYy

RRyy

RrYy

Rryy

rY

RrYY

RrYy

rrYY

rrYy

ry

RrYy

Rryy

rrYy

rryy

4. Match up genes from both parents: Rr Yy

Rr Yy

RY

Ry

rY

ry

RY

RRYY

RRYy

RrYY

RrYy

Ry

RRYy

RRyy RrYy

Rryy

rY

RrYY

RrYy

rrYy

ry

RrYy

Rryy

rrYY rrYy

rryy

5. Count and analyze the offspring: Rr Yy RY RY Rr Yy

Ry rY ry

Ry

rY

ry

5. Count and analyze the offspring: 9 9 smooth + yellow

1

2

6

5 7 9

3

8

4

5. Count and analyze the offspring: 9 9 smooth + yellow

3 3 smooth + green

1

2

3

4

5

1

6

2

7

8

1

2

9

3

3

5. Count and analyze the offspring: 9 9 smooth + yellow

3 3 smooth + green

1

2

3

4

5

1

6

2

7

8

1

2

9

3

3

3 3 wrinkled + yellow

5. Count and analyze the offspring: 9 9 smooth + yellow

3 3 smooth + green

1

2

3

4

5

1

6

2

7

8

1

2

9

3

3

1

3 3 wrinkled + yellow

1 1 wrinkled + green

5. Count and analyze the offspring: 9 9 smooth + yellow

3 3 smooth + green

3 3 wrinkled + yellow

1 1 wrinkled + green

A DIHYBRID CROSS RESULTS IN A

5. Count and analyze the offspring: 9 9 smooth + yellow

A DIHYBRID CROSS RESULTS IN A

3 3 smooth + green

3 3 wrinkled + yellow

1 1 wrinkled + green

9:3 :3:1 RATIO

5. Count and analyze the offspring: 9 9 smooth + yellow

A DIHYBRID CROSS RESULTS IN A

3 3 smooth + green

3

9:3 :3:1 RATIO

3 wrinkled + yellow

1 1 wrinkled + green

(If there is complete dominance)

REVIEW CHECKPOINT:

REVIEW CHECKPOINT: 1. What is meant by a “dihybrid” ?

REVIEW CHECKPOINT: 1. What is meant by a “dihybrid” ?

2. How many different gamete genotypes are possible in a dihybrid cross ?

REVIEW CHECKPOINT: 1. What is meant by a “dihybrid” ?

2. How many different gamete genotypes are possible in a dihybrid cross ?

3. How many boxes are needed in a dihybrid Punnett Square ?

REVIEW CHECKPOINT: 1. What is meant by a “dihybrid” ?

2. How many different gamete genotypes are possible in a dihybrid cross ?

3. How many boxes are needed in a dihybrid Punnett Square ?

4. What are the ratios of possible offspring from a dihybrid cross ?

REVIEW CHECKPOINT: 1. What is meant by a “dihybrid” ?

2. How many different gamete genotypes are possible in a dihybrid cross ?

3. How many boxes are needed in a dihybrid Punnett Square ?

4. What are the ratios of possible offspring from a dihybrid cross ?

5. Show a cross between a pure wrinkled green pea plant and a pure round and yellow pea plant. Give ratios for offspring.

REVIEW CHECKPOINT: 6. Big feet are dominant over small feet in kangaroos. Similarly, tall ears are dominant over short ears. Show a cross between two hybrid kangaroos and give the ratios of expected baby kanga’s.

REVIEW CHECKPOINT: 6. Big feet are dominant over small feet in kangaroos. Similarly, tall ears are dominant over short ears. Show a cross between two hybrid kangaroos and give the ratios of expected baby kanga’s.

7. In buffalo, a cross between a black and a white give brown coat baby buffalo. And long horn buffalos crossed with shorties give medium horns. Give the ratios of expected offspring from two brown & medium horny buff’s.