Predict traits with a Punnett square

Answer Key - Grade 7 Science Worksheet

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

1. 1.

   Bo makes a Punnett square for Tt × Tt pea plants. What is the chance an offspring is dwarf, as a percent?

   25
2. 2.

   Esme makes a Punnett square for YY × Yy pea plants. What is the chance an offspring seed is yellow, as a percent?

   100
3. 3.

   T = tall (dominant), t = dwarf (recessive). Cross: Tt × tt. Kira predicts the offspring of a Tt × tt pea cross. Which ratio of tall to dwarf is expected?

   • 1 tall to 1 dwarf
   • 1 TT to 2 Tt to 1 tt
   • 3 tall to 1 dwarf
   • Medium-height plants
4. 4.

   Y = yellow (dominant), y = green (recessive). Cross: Yy × Yy. Luz predicts the seed colors from a Yy × Yy pea cross. Which ratio of yellow to green is expected?

   • Yellow-green seeds
   • 3 yellow to 1 green
   • 1 yellow to 1 green
   • 1 YY to 2 Yy to 1 yy
5. 5.

   Every offspring Vv, violet flowers. V = violet (dominant), v = white (recessive). Milo reads that every offspring of a pea cross is violet with the letters Vv. Which parents fit?

   • VV × VV: two pure violet parents
   • VV × vv: pure violet and white
   • vv × vv: two white parents
   • Vv × Vv: two mixed parents
6. 6.

   21 tall, 19 dwarf. T = tall (dominant), t = dwarf (recessive). Noah reads that about half the offspring of a pea cross are tall and half are dwarf. Which parents fit?

   • TT × tt: pure tall and dwarf
   • Tt × tt: mixed tall and dwarf
   • TT × TT: two pure tall parents
   • Tt × Tt: two mixed tall parents
7. 7.

   Mostly round seeds, some wrinkled. Both parents have round seeds. R = round (dominant), r = wrinkled (recessive). Pia reads that two round-seeded pea plants had some wrinkled seeds. Which parents fit?

   • RR × Rr: pure round and mixed
   • rr × rr: two wrinkled parents
   • Rr × Rr: two mixed round parents
   • RR × RR: two pure round parents
8. 8.

   Ren grows seedlings from a Tt × Tt cross. The first three are tall. What is the chance the next one is dwarf?

   • 1 in 3, since three are done
   • 1 in 4, the same as for each seedling
   • Certain: one in four seedlings has to be dwarf
   • Zero: this cross makes tall plants
9. 9.

   Tala has 4 seeds from one Rr × Rr cross. Must exactly 3 of them be round?

   • No: the 4 seeds will match each other
   • Yes: unless a seed blends into a new shape
   • Yes: the square promises 3 round in each 4
   • No: each seed has a 3 in 4 chance, so counts vary
10. 10.

    Zee grows plants from a Vv × vv cross. The first two have white flowers. What is the chance the third is violet?

    • Zero, since white keeps showing up
    • 1 in 2, the same as each time
    • 1 in 4, as in a Vv × Vv cross
    • Above 1 in 2, to balance the two white