Predict traits with a Punnett square

Answer Key - Grade 7 Science Worksheet - Challenge Me

Circle the best answer, or write your answer on the line.

1. 1.

   Ari’s class plants 40 seeds from a Tt × Tt pea cross. About how many plants would you expect to be dwarf?

   10
2. 2.

   Bo reads about 80 seeds from one Rr × Rr pea cross. About how many would you expect to be round?

   60
3. 3.

   Esme reads about 60 seeds from a Yy × Yy pea cross. About how many would you expect to be green?

   15
4. 4.

   Second-generation pea plants, 705 violet and 224 white. V = violet (dominant), v = white (recessive). Jun reads Mendel’s real counts for pea flower color in the second generation. About what ratio is this, and what were the parents’ letters?

   • About 3 to 1, so both parents were mixed, Vv
   • About 3 to 1, so both parents were pure violet, VV
   • About 1 to 1, so the parents were Vv × vv
   • About 1 to 2 to 1, so the colors blended
5. 5.

   705 violet, 224 white; ratio about 3.15 to 1. Kira sees that Mendel’s 705 to 224 is about 3.15 to 1, not exactly 3 to 1. Why?

   • Some flowers blended into pale violet
   • He miscounted the plants, since the square promises 3 to 1
   • Chance decides each plant, so counts vary near 3 to 1
   • The Punnett square is wrong for peas

6. Read this first

   Results card (model data)

   120 plants from a Tt × Tt pea cross: 88 tall, 32 dwarf. A 3 to 1 split of 120 is 90 and 30.

7. 6.

   Luz’s class grew 120 plants from a Tt × Tt cross and got 88 tall and 32 dwarf. Do the results fit the square?

   • No: it has to be exactly 90 and 30
   • Yes: it shows tall and dwarf blending
   • No: it should be 60 tall and 60 dwarf
   • Yes: 88 to 32 is close to 3 to 1
8. 7.

   Violet parent (letters unknown) × white parent (vv). Offspring: 40 violet, 0 white. Milo reads about a violet pea plant with unknown letters crossed with a white (vv) plant. All 40 offspring are violet. What are its letters, most likely?

   • Most likely VV, because no white offspring appeared
   • Vv, since half the offspring should blend to pale violet
   • Vv, because violet is dominant
   • vv, since a white parent was used
9. 8.

   Pia asks why a test cross pairs the unknown violet plant with a white (vv) plant, not another violet plant. Which answer is best?

   • A violet partner would promise an exact count
   • vv gives only v, so a hidden v shows up as white
   • White plants make more seeds than violet ones
   • The white plant blends the colors so the hidden ones show
10. 9.

    V = violet (dominant), v = white (recessive). Cross: VV × Vv. Ren’s friend says Vv pea plants have pale violet flowers, a blend of the two colors. Which response is best?

    • Disagree: Vv looks like VV, because V is dominant
    • Agree: each letter adds half its color
    • Agree: Vv shows white with a violet edge
    • Disagree: Vv flowers are white, since v hides V
11. 10.

    V = violet (dominant), v = white (recessive). Cross: Vv × Vv. Zee’s friend says two violet pea plants cannot have a white offspring. Which response is best?

    • Agree: white offspring need white parents
    • Agree: violet is dominant, so violet passes on each time
    • Disagree: the colors blend and then split apart
    • Disagree: two Vv parents can each pass v, giving vv