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9th grade Mendel's laws of segregation and independent assortment worksheet

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Mendel's laws of segregation and independent assortment

Grade 9 Science Worksheet

NameDate

Circle the best answer.

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

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

  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
    • 3 in 4
    • 1 in 3, since there are three kinds of seed

  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. 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?

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

  5. Read this first

    Two genes on different chromosomes (model)

    geneeach parent's alleleswhere the gene sits
    seed colorYyone chromosome
    seed shapeRra different chromosome

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

    • 80 seeds
    • 160 seeds
    • 240 seeds
    • 180 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. 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
    • Not known, since 24 and 26 are not exactly 1 : 1
    • Vv (one violet, one white allele), since about half are white

  9. Two possible test cross partners (model)

    partner plantalleles its gametes can carry
    vvv
    VvV or v

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

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

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

    generationtall plantsdwarf plants
    F2787277

  12. 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 0.35 : 1
    • About 2.84 : 1, which does not fit 3 : 1
    • About 3.84 : 1

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

    generationround seedswrinkled seedsseeds in all
    F25,4741,8507,324

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

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

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

    characteristicplants with the dominant traitplants with the recessive trait
    flower color705224
    plant height787277
    seed color6,0222,001

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

    • Seed color, about 3.01 : 1
    • Each of them, since each ratio is exactly 3 : 1
    • Flower color, about 3.15 : 1
    • Plant height, about 2.84 : 1
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9th grade Mendel's laws of segregation and independent assortment worksheet – printable
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About this worksheet

Mendel's laws: segregation, independent assortment and monohybrid ratios. Every version has 10 questions, and the answer key prints on the second page.

What your child will learn

  • I can say what true-breeding, P, F1 and F2 mean in a pea cross, and place a box of a cross diagram in its generation.
  • I can say what dominant and recessive mean, and why a plant with one dominant and one recessive allele shows the dominant trait.
  • I can state the law of segregation (the two alleles of a gene separate, so each offspring gets one from each parent), the law of dominance, and the law of independent assortment (alleles of genes on different chromosomes are passed on separately), and match each to a case.
  • I can fill a 2 by 2 square for two heterozygous parents and give both ratios: genotypes 1 : 2 : 1 and phenotypes 3 : 1, and say which one a question asks for.
  • I can turn a ratio into an expected count out of a total (3/4 of 400 is 300) and know that a real count lands near the expected count, not on it.
  • I can read a test cross: all offspring show the dominant trait points to a homozygous dominant parent, and about half showing the recessive trait points to a heterozygous parent.

Standard: HS-LS3-3

Words to know

true-breeding: A plant line that always gives offspring like itself when crossed with itself

P, F1, F2: The parent plants, their offspring, and the offspring of those offspring

allele: One form of a gene, such as V or v

dominant, recessive: The allele that shows when present, and the one that shows only as a pair

genotype, phenotype: The pair of letters, and the look or trait you can see

homozygous, heterozygous: Two same letters (VV, vv), and two different letters (Vv)

Punnett square: A grid of every equally likely way two parents' alleles can pair up

law of segregation: The two alleles of a gene separate, one to each offspring from each parent

Common mistakes

Your child thought real counts must match a ratio exactly, so a count near 3 : 1 looked like a failure. Counts that come from chance land near the ratio, not on it. Ask your child how close 705 and 224 are to a 3 : 1 split.

Your child expected the two alleles of a hybrid to blend into an in-between look, such as pale violet. In Mendel's peas the dominant trait shows and the traits stay separate. Ask your child what color a Vv flower is.

Your child thought a recessive trait is lost when it does not show in the F1. The allele is still there, hidden, and it can show again in the F2. Ask your child where the 224 white plants came from.

Questions parents ask

What is the most common mistake with mendel's laws of segregation and independent assortment?

Your child thought real counts must match a ratio exactly, so a count near 3 : 1 looked like a failure. Counts that come from chance land near the ratio, not on it. Ask your child how close 705 and 224 are to a 3 : 1 split.

Are these 9th grade science worksheets free to print?

Yes. All 6 printable versions at each level are free to print, with the answer key, and no account is needed.

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