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?

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

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

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

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

   • 200 seeds
   • 75 seeds
   • 300 seeds
   • 100 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?

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

5. Read this first

   Two genes on different chromosomes (model)

   gene	each parent's alleles	where the gene sits
   seed color	Yy	one chromosome
   seed shape	Rr	a different chromosome

6. 5.

   Model data: Luz's class plants 320 seeds from YyRr × YyRr parents. About how many seeds are expected to be yellow, whatever their shape?

   • 160 seeds
   • 180 seeds
   • 240 seeds
   • 80 seeds

7. 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.

8. 6.

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

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

9. 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.

10. 7.

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

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

11. Two possible test cross partners (model)

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

12. 8.

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

    • 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 has the dominant trait, so the offspring look violet
    • A Vv partner works as well, since it also has a v allele

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

    generation	tall plants	dwarf plants
    F2	787	277

14. 9.

    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

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?

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