Mendel's laws of segregation and independent assortment

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. 1.

   Ari picks one violet-flowered offspring of two Vv plants at random. What is the chance that it is Vv?

   • 2 in 3, since 2 of the 3 violet boxes are Vv
   • 1 in 3, since 1 of the 3 violet boxes is a Vv plant
   • 3 in 4, since 3 of the 4 boxes are violet
   • 1 in 2, since 2 of the 4 boxes are Vv
2. 2.

   Bo crosses a round plant with a wrinkled plant (rr). If the round plant is Rr, what is the chance that three offspring in a row are all round?

   • 3 in 4
   • 1 in 4
   • 1 in 2
   • 1 in 8

3. Read this first

   Two genes on different chromosomes (model)

   gene	each parent's alleles	where the gene sits
   flower position	Aa	one chromosome
   pod color	Gg	a different chromosome

4. 3.

   Esme crosses two AaGg plants (A for axial flowers, a for terminal; G for green pods, g for yellow). What is the chance one offspring has terminal flowers and yellow pods?

   • 9 in 16
   • 1 in 2, since 1/4 + 1/4
   • 1 in 4
   • 1 in 16

5. Cross card

   A cross of two tall plants (model data), 1 row. Columns: parents, offspring. Row 1: two tall plants, letters unknown, 30 tall and 10 dwarf.

6. 4.

   Kira reads a cross card for two tall pea plants. What are the parents' letters, most likely?

   • Tt × tt (one parent has two dwarf alleles)
   • TT × Tt (one parent has two tall alleles)
   • TT × TT (both parents have two tall alleles)
   • Tt × Tt (each parent has one tall, one dwarf allele)

7. Cross card

   A surprise dwarf plant (model data), 1 row. Columns: parents, one offspring. Row 1: two tall plants, letters unknown, a dwarf plant.

8. 5.

   Two tall pea plants have one dwarf offspring. Luz asks what must be true of both parents.

   • Both are TT, since a tall plant has lost its dwarf allele
   • Neither has a dwarf allele; the heights blended into a small plant
   • Both carry a dwarf allele, so both are Tt
   • One needs a dwarf allele, so TT × Tt could do it

9. Notebook

   Notes on two Vv plants (classmate's notebook), 4 lines. Columns: line, entry. Line 1: Each Vv parent passes on one of its two alleles, chosen at random. Line 2: So the four boxes are VV, Vv, Vv and vv. Line 3: The three kinds of genotype are in the ratio 3 : 1. Line 4: The phenotypes are 3 violet to 1 white.

10. 6.

    Milo reads a classmate's notebook about two Vv pea plants. Which line has the mistake?

    • Line 2: the two Vv boxes should be counted as one
    • Line 4: the phenotypes are in the ratio 1 : 2 : 1
    • Line 1: a parent should pass on both of its alleles
    • Line 3: the genotypes are in the ratio 1 : 2 : 1

11. Notebook

    Notes on Mendel's flower cross (classmate's notebook), 4 lines. Columns: line, entry. Line 1: Mendel crossed true-breeding violet plants with true-breeding white plants. Line 2: All the F1 plants had violet flowers, so the white allele was lost for good. Line 3: F1 plants crossed with themselves gave 705 violet and 224 white in the F2. Line 4: So the white allele was in the F1 plants, hidden by the violet allele.

12. 7.

    Noah reads a classmate's notebook about Mendel's flower-color cross. Which line has the mistake?

    • Line 4: an allele that does not show cannot be in a plant
    • Line 2: the white allele was hidden in the F1, not lost
    • Line 3: the counts 705 and 224 should be about equal
    • Line 1: Mendel should have used plants that were not true-breeding
13. 8.

    Ren says: two Vv parents with four offspring will have exactly 3 violet and 1 white. Do you agree?

    • Yes, because the square has 3 violet boxes and 1 white box
    • No, because each offspring has a 3 in 4 chance of violet, so four can differ
    • No, because the ratio of looks is 1 : 2 : 1, not 3 : 1
    • Yes, because a 3 : 1 ratio fixes the numbers in a family of four

14. Mendel's real counts, flower color (real data: Mendel)

    generation	what the plants showed
    F1	100 percent violet
    F2	705 violet and 224 white

15. 9.

    Tala claims that the F1 plants lost the white allele. Do you agree?

    • No, because the F1 flowers were pale violet, a blend
    • No, because 224 white F2 plants show the allele was still there
    • Yes, because 705 : 224 is not exactly 3 : 1
    • Yes, because 100 percent of the F1 plants had violet flowers
16. 10.

    Two Vv parents have three violet offspring so far. Zee says the next one must be white to make 3 : 1. Do you agree?

    • No, because the next offspring is violet with chance 3 in 4, as before
    • Yes, because the square has one white box left
    • Yes, because a family has to match the 3 : 1 ratio
    • No, because the next offspring is Vv, which blends violet and white