Genetics YEAR 12 BIOLOGY Originally created by Bob Perry, Malibu High School Modified by John Cary, Malibu High School

Dihybrid Crosses: or predicting 2 traits at a time

characteristics of garden peas. Gregor Mendel studied 7 characteristics of garden peas.

Let’s see how to predict crosses with TWO traits at a time: Gregor Mendel studied 7 characteristics of garden peas.

RECALL THAT ROUND & YELLOW ARE BOTH DOMINANT TRAITS. 1. Choose symbols: RR = round Rr = round r r = wrinkled SEED SHAPE YY = yellow Yy = yellow y y = green SEED COLOR RECALL THAT ROUND & YELLOW ARE BOTH DOMINANT TRAITS.

CROSS BETWEEN 2 ROUND & YELLOW WE WILL WORK A DIHYBRID CROSS BETWEEN 2 ROUND & YELLOW HYBRID PEAS. Rr Yy (BOTH PARENTS WILL HAVE THE SAME GENOTYPE IN THIS PROBLEM)

Notice there are now FOUR different genetic possibilities for a gamete 1. Write gamete genotypes using Mendel’s Principle of Independent Assortment: Parental Genotype Both parents Rr Yy Ry rY ry RY Notice there are now FOUR different genetic possibilities for a gamete possible Gamete genes

2. Make a 16 square Punnett Square: female genotype and gametes Rr Yy RY Ry rY ry male genotype and gametes RY Ry Rr Yy rY ry

3. Match up genes from both parents: Rr Yy RY Ry rY ry RRYy RrYY RrYy RY RRYY Ry RRYy RRyy RrYy Rryy Rr Yy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy

4. Match up genes from both parents: Rr Yy RY Ry rY ry RRYy RrYY RrYy RY RRYY RRyy Ry RRYy RrYy Rryy Rr Yy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy

5. Count and analyze the offspring: Rr Yy RY Ry rY ry RY Ry Rr Yy rY ry

5. Count and analyze the offspring: 9 9 smooth + yellow 1 2 3 4 3 3 smooth + green 6 5 1 2 3 7 1 2 8 3 wrinkled + yellow 1 9 3 3 1 1 wrinkled + green

9 : 3 : 3 : 1 RATIO A DIHYBRID CROSS RESULTS IN A 5. Count and analyze the offspring: 9 A DIHYBRID CROSS RESULTS IN A 9 smooth + yellow 3 3 smooth + green 9 : 3 : 3 : 1 RATIO 3 3 wrinkled + yellow (If there is complete dominance) 1 1 wrinkled + green

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 yellow and round 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. 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.