Two-trait crosses with a 4 by 4 square
Grade 9 Science Worksheet - Challenge Me
Circle the best answer.
Ren test-crosses a round yellow plant (RrYy) with a wrinkled green plant (rryy). What phenotype ratio does the square predict?
- 1 : 1 : 1 : 1
- 3 : 1
- 1 : 1
- 9 : 3 : 3 : 1
Read this first
Test cross (model data)
Plant X, a round yellow plant of unknown genotype, crossed with a wrinkled green plant (rryy). Offspring: 26 round yellow, 24 round green, 25 wrinkled yellow, 25 wrinkled green. Total: 100. Table: Test cross counts (model data); columns offspring and number of plants; rows round yellow, round green, wrinkled yellow, wrinkled green, total.
Jun reads the model counts from a test cross of plant X with a wrinkled green plant (rryy). Which genotype is plant X?
- RRYy (R: two capital; Y: one capital, one small)
- RrYY (R: one capital, one small; Y: two capital)
- RRYY (R: two capital; Y: two capital)
- RrYy (R: one capital, one small; Y: one capital, one small)
Test cross (model data)
Plant X, a round yellow plant of unknown genotype, crossed with a wrinkled green plant (rryy). Offspring: 51 round yellow, 0 round green, 49 wrinkled yellow, 0 wrinkled green. Total: 100. Table: Test cross counts (model data); columns offspring and number of plants; rows round yellow, round green, wrinkled yellow, wrinkled green, total.
Kira reads the model counts from another test cross of a round yellow plant X with a wrinkled green plant (rryy). Which genotype is plant X?
- RrYY (R: one capital, one small; Y: two capital)
- RRYy (R: two capital; Y: one capital, one small)
- RRYY (R: two capital; Y: two capital)
- RrYy (R: one capital, one small; Y: one capital, one small)
Use this
Example counts, a table of offspring and number of plants, from a textbook and not Mendel's own: tall inflated 2,706; tall constricted 930; dwarf inflated 888; dwarf constricted 300. Tall (T) and inflated pods (I) are dominant; dwarf (t) and constricted pods (i) are recessive. Divide each count by 300 and round to whole numbers.
Milo reads example counts from TtIi × TtIi pea plants. Dividing each count by 300, the smallest, and rounding, which ratio is closest?
- 9 : 3 : 1 : 3
- 9 : 3 : 3 : 1
- 3 : 1
- 1 : 1 : 1 : 1
Notebook for RrYy × RrYy
Line 1: Each parent passes on 4 combinations. Line 2: The square has 4 × 4 = 16 boxes. Line 3: Round green fills 3 boxes. Line 4: The chance of round green is 3/4 + 1/4 = 1. Table: Notebook for RrYy × RrYy; columns line and what the notebook says; rows 1, 2, 3, 4.
Tala's notebook is about one RrYy × RrYy cross. One line is wrong. Which fix is right?
- Line 4 should multiply: 3/4 × 1/4 = 3/16
- Line 2 should say the square has 4 + 4 = 8 boxes
- Line 3 should say round green fills 9 boxes
- Line 1 should say each parent passes on 2 combinations
Notebook for a test cross
Line 1: The cross is RrYy × rryy. Line 2: The rryy plant passes on only ry. Line 3: The square has 4 boxes, one for each combination of the RrYy plant. Line 4: The offspring come out 9 : 3 : 3 : 1. Table: Notebook for a test cross; columns line and what the notebook says; rows 1, 2, 3, 4.
Zee's notebook is about a test cross. One line is wrong. Which fix is right?
- Line 3 should say the square has 16 boxes
- Line 2 should say the rryy plant passes on RY, Ry, rY and ry
- Line 4 should say the offspring come out 1 : 1 : 1 : 1
- Line 1 should say the cross is RrYy × RrYy
Notebook for 480 seeds from RrYy × RrYy
Line 1: Round yellow fills 9 of 16 boxes. Line 2: Wrinkled green fills 1 of 16 boxes. Line 3: Expected wrinkled green: 480 ÷ 16 = 30 seeds. Line 4: Expected round yellow: 9 × 480 = 4,320 seeds. Table: Notebook for 480 seeds; columns line and what the notebook says; rows 1, 2, 3, 4.
Ari's notebook scales a model total of 480 seeds from RrYy × RrYy. One line is wrong. Which fix is right?
- Line 2 should say wrinkled green fills 3 of 16 boxes
- Line 3 should say 480 ÷ 4 = 120 seeds
- Line 1 should say round yellow fills 3 of 16 boxes
- Line 4 should say 9 ÷ 16 × 480 = 270 seeds
Claim card
RrYy × RrYy always gives 9 : 3 : 3 : 1. Both genes show simple dominance (R over r, Y over y). The seed shape gene and the seed color gene can be on different chromosomes or on the same one. Table: Claim card; columns claim and cross; rows always 9 : 3 : 3 : 1.
Esme claims that two plants with RrYy always give 9 : 3 : 3 : 1, with simple dominance for both genes. Which reply has the correct reason?
- Yes, because the dominant alleles stay together when passed on
- Yes, because the 16 boxes are the same for any two genes
- No: the ratio needs the two genes to sort independently, as genes on different chromosomes do
- No, because two genes followed together give 3 : 1
Model data
32 plants from RrYy × RrYy. Found: 1 wrinkled green plant. Prediction: wrinkled green fills 1 box of 16, so 32 ÷ 16 = 2 plants are expected. Table: Claim card; columns item and plants; rows plants grown, boxes in the square, wrinkled green found, wrinkled green expected.
Bo grows 32 plants from RrYy × RrYy (model data) and finds 1 wrinkled green plant. The claim is that the 1/16 prediction is wrong. Which reply is best?
- The claim is weak, because 18 are expected
- The claim is right, because exactly 2 must appear
- The claim is right, because the expected number is 8
- The claim is weak: 2 are expected, and a count near 2 can happen by chance in a small group
Claim card: a test cross of RrYy with rryy shows the four allele combinations RrYy can pass on. Jun claims that a test cross of RrYy with rryy shows the four combinations RrYy can pass on. Which reason supports the claim?
- The rryy plant passes on its own gene pairs, rr and yy, so the offspring copy them
- The rryy plant passes on only ry, so each offspring shows one combination from the other plant
- The offspring come out 9 : 3 : 3 : 1, which shows the combinations
- The RY combination stays together, so only RY and ry offspring appear