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.