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?

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

   Bo crosses two Tt pea plants. What is the ratio of tall plants to dwarf plants in the offspring?

   • 1 tall : 2 mixed : 1 dwarf
   • 1 tall : 1 dwarf
   • 3 tall : 1 dwarf
   • 1 tall : 3 dwarf
4. 3.

   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 4, since only yy is green
   • 1 in 2, since a y makes a seed green
5. 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?

   Use the picture in question 3.

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

6. 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

7. 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?

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

8. 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.

9. 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

10. Two possible test cross partners (model)

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

11. 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 works as well, since it also has a v allele
    • A vv partner blends with the unknown plant, so the offspring look pale

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

    generation	tall plants	dwarf plants
    F2	787	277

13. 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 2.84 : 1, which does not fit 3 : 1
    • About 0.35 : 1
    • About 3.84 : 1

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

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

15. 9.

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

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

16. 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

17. 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
    • Each of them, since each ratio is exactly 3 : 1
    • Seed color, about 3.01 : 1
    • Plant height, about 2.84 : 1