Mendel's laws of segregation and independent assortment

Grade 9 Science Worksheet

Circle the best answer.

1. 1.

   Ari fills the square for two Vv pea plants and counts the genotypes. What is the genotype ratio?

   • 3 : 1
   • 2 : 1 : 1
   • 1 : 2 : 1
   • 1 : 1 : 1
2. 2.

   Esme crosses two Yy pea plants. What is the chance that one offspring seed is green?

   • 3 in 4
   • 1 in 3, since there are three kinds of seed
   • 1 in 2, since a y makes a seed green
   • 1 in 4, since only yy is green
3. 3.

   Model data: Jun's class plants 400 seeds from Rr × Rr parents. About how many seeds are expected to be round?

   • 100 seeds
   • 300 seeds
   • 200 seeds
   • 75 seeds
4. 4.

   Model data: Kira's class plants 120 seeds from Yy × Yy parents. About how many seeds are expected to be Yy, with one yellow and one green allele?

   • 40 seeds
   • 60 seeds
   • 30 seeds
   • 90 seeds

5. Read this first

   Test cross card

   A test cross (model data), 1 row. Columns: plant crossed with a white-flowered vv plant, offspring. Row 1: violet-flowered plant, letters unknown, 24 violet and 26 white.

6. 5.

   Milo reads a test cross card. What are the letters of the violet-flowered plant, most likely?

   • VV (two violet alleles), since the plant is violet
   • vv (two white alleles), since white offspring appeared
   • Vv (one violet, one white allele), since about half are white
   • Not known, since 24 and 26 are not exactly 1 : 1

7. Test cross card

   Another test cross (model data), 1 row. Columns: plant crossed with a wrinkled-seeded rr plant, offspring. Row 1: round-seeded plant, letters unknown, 31 round and 0 wrinkled.

8. 6.

   Noah reads a second test cross card. What are the letters of the round-seeded plant, most likely?

   • Rr (one round, one wrinkled allele), since round is dominant
   • rr (two wrinkled alleles), since the partner was rr
   • RR (two round alleles), since no wrinkled seeds appeared
   • Not known, since a test cross needs a wrinkled seed

9. Two possible test cross partners (model)

   partner plant	alleles its gametes can carry
   vv	v
   Vv	V or v

10. 7.

    Pia compares two partners for a test cross. Why is a vv partner better than a Vv partner?

    • A vv partner has the dominant trait, so the offspring look violet
    • A vv partner passes on only v, so each offspring shows the other plant's allele
    • A vv partner blends with the unknown plant, so the offspring look pale
    • A Vv partner works as well, since it also has a v allele

11. Mendel's real counts, plant height (real data: Mendel)

    generation	tall plants	dwarf plants
    F2	787	277

12. 8.

    Ren divides Mendel's F2 plant-height counts. About what is the ratio of tall plants to dwarf plants?

    • About 2.84 : 1, close to 3 : 1
    • About 3.84 : 1
    • About 2.84 : 1, which does not fit 3 : 1
    • About 0.35 : 1

13. Mendel's real counts, seed shape (real data: Mendel)

    generation	round seeds	wrinkled seeds	seeds in all
    F2	5,474	1,850	7,324

14. 9.

    Tala wants the count that a 3 : 1 ratio predicts. How many round seeds does 3/4 of the total give?

    • 2,441 seeds
    • 5,493 seeds, close to Mendel's count
    • 1,831 seeds
    • 5,474 seeds, since the prediction must equal the count

15. Mendel's real F2 counts (real data: Mendel)

    characteristic	plants with the dominant trait	plants with the recessive trait
    flower color	705	224
    plant height	787	277
    seed color	6,022	2,001

16. 10.

    Zee divides each row of Mendel's F2 counts. Which characteristic has a ratio closest to 3 : 1?

    • Flower color, about 3.15 : 1
    • Plant height, about 2.84 : 1
    • Each of them, since each ratio is exactly 3 : 1
    • Seed color, about 3.01 : 1