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9th grade Sex-linked traits and reading a pedigree worksheet

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Sex-linked traits and reading a pedigree

Grade 9 Science Worksheet - Building Confidence

NameDate

Circle the best answer.

  1. Read this first

    Table

    Color vision rules (model), 4 rows. Columns: item, rule. Row 1: XB, typical color vision allele, dominant. Row 2: Xb, red-green color vision difference allele, recessive. Row 3: XX, two X chromosomes. Row 4: XY, one X chromosome and one Y chromosome.

  2. Ari reads a rule card for a model family. Which color vision does an XX individual with the genotype XBXb show?

    • No color vision (the two alleles cancel out)
    • A mix of typical and different color vision (the alleles blend)
    • Typical color vision (XB is dominant to Xb)
    • The red-green color vision difference (the genotype holds an Xb)

  3. Table

    XY individual card (model), 3 rows. Columns: item, rule. Row 1: Xb, red-green color vision difference allele, recessive. Row 2: Y, no copy of this gene. Row 3: XY, one X chromosome and one Y chromosome.

  4. Bo reads a card about an XY individual in a model family. What does the genotype XbY show?

    • Typical color vision, as a carrier of the Xb allele
    • Typical color vision (the Y carries a dominant allele)
    • The red-green color vision difference (the only allele is Xb)
    • A mix of typical and different color vision

  5. Gene location card (model)

    genelocation
    red-green color vision genesX chromosome
    Y chromosomeno copy of these genes

  6. Esme reads a gene card. The color vision genes sit on the X chromosome and not on the Y. What is this pattern called?

    • X-linked inheritance (the genes sit on the X)
    • Recessive inheritance (the allele is hidden)
    • Y-linked inheritance (the genes sit on the Y)
    • Autosomal inheritance (the genes sit on a non-sex pair)

  7. Jun fills a Punnett square for a model color vision cross. Which genotype goes in the blank box?

    • XbY (a difference allele and a Y)
    • XBXb (a typical and a difference allele)
    • XBY (a typical allele and a Y)
    • XbXb (two difference alleles)

  8. Kira fills a Punnett square for a model color vision cross. Which genotype goes in the blank box?

    • XBY (a typical allele and a Y)
    • XBXB (two typical alleles)
    • XBXb (a typical and a difference allele)
    • XbY (a difference allele and a Y)

  9. Table

    Two kinds of individuals (model), 2 rows. Columns: kind, X chromosomes, alleles for an X-linked gene. Row 1: XX, 2, two alleles. Row 2: XY, 1, one allele, since the Y has no copy.

  10. Milo reads a card. Why can a single Xb allele show the trait in an XY individual?

    • No second allele is there to cover it
    • The Y chromosome adds a second Xb allele
    • Xb becomes dominant in an XY individual
    • XX and XY individuals show it equally often anyway

  11. Table

    Alleles card (model), 2 rows. Columns: item, rule. Row 1: XB, typical color vision allele, dominant. Row 2: Xb, red-green color vision difference allele, recessive.

  12. Pia reads an allele card for a model family. Which description fits a carrier of the Xb allele?

    • An XY individual with Xb and a Y, who shows typical color vision
    • An XX individual with XB and XB, who has no Xb
    • An XX individual with XB and Xb, who shows typical color vision
    • An XX individual with Xb and Xb, who shows the trait

  13. Use this

    squares are XY individuals, circles are XX individuals, a filled symbol has the trait, a circle with a dot is a marked carrier; a circle with no dot is not marked either way.

  15. Ren reads a made-up pedigree. II-2 is a filled square. Which description fits II-2?

    • An XX individual with the red-green color vision difference
    • An XY individual with the red-green color vision difference
    • An XY individual who is a carrier of the Xb allele
    • An XY individual with typical color vision

  16. Tala reads the same made-up pedigree. I-2 is a circle with a dot. Which description fits I-2?

    Use the picture in question 8.

    • An XX carrier of the Xb allele, with typical color vision
    • An XY carrier of the Xb allele, with typical color vision
    • An XX individual with the red-green color vision difference
    • An XX individual with two XB alleles and no Xb

  17. Use this

    Pedigree of a made-up family for the red-green color vision difference (squares are XY individuals, circles are XX individuals, a filled symbol has the trait, a circle with a dot is a marked carrier; a circle with no dot is not marked either way).

  18. Zee reads another made-up pedigree. How many individuals in it have the red-green color vision difference?

    • 3 individuals
    • 1 individual
    • 5 individuals
    • 2 individuals
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9th grade Sex-linked traits and reading a pedigree worksheet – printable
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About this worksheet

Sex-linked traits and pedigrees: XX and XY, carriers and reading a made-up family. Every version has 10 questions, and the answer key prints on the second page.

What your child will learn

  • I can say that an XX individual has two X chromosomes and an XY individual has one X and one Y, and that the Y chromosome has no copy of an X-linked gene.
  • I can say what X-linked means: the gene sits on the X chromosome and not on the Y.
  • I can read the genotypes XBXB, XBXb, XbXb, XBY and XbY (XB dominant, Xb recessive), say what each shows, and say that an XY individual has only one allele for an X-linked gene, so a single Xb shows.
  • I can fill and read a 2 by 2 grid with X and Y cards for XBXb × XBY, XBXB × XbY, XBXb × XbY and the fruit fly crosses XWXw × XwY and XwXw × XWY, and turn it into statements by sex (for example, half of the XY offspring have the trait and no XX offspring do).
  • I can say which parent gives an XY offspring its X (the XX parent) and why the XY parent gives it a Y.
  • I can say what a carrier is (an XX individual with one dominant and one recessive allele, who does not show the trait in this model) and that an XY individual with one Xb has the trait and is not a carrier.

Standard: HS-LS3-3

Words to know

sex chromosomes: The pair that differs between XX and XY individuals: two X chromosomes, or an X and a Y

autosomes: The 22 other pairs of chromosomes

X-linked: A gene that sits on the X chromosome and not on the Y

allele: One form of a gene, such as XB or Xb

genotype: The alleles one individual carries, such as XBXb or XbY

carrier: An XX individual with one recessive allele who does not show the trait

dominant, recessive: The allele that shows when present, and the one that shows only when no dominant allele is there

trait: A feature a gene helps set, such as eye color or red-green color vision

Common mistakes

Your child treated the Y chromosome as if it held an allele that pairs with or covers the X allele. The Y has no copy of these genes, so one Xb in an XY individual shows. Ask your child how many alleles an XY individual has for an X-linked gene.

Your child thought an XY parent passes its X to an XY child. An XY parent passes a Y to an XY child and its X to an XX child. Ask your child which chromosome an XY child gets from each parent.

Your child thought a carrier shows the trait. A carrier has one recessive allele beside a dominant one, so the trait stays hidden. Ask your child what an XBXb individual shows.

Questions parents ask

What is the most common mistake with sex-linked traits and reading a pedigree?

Your child treated the Y chromosome as if it held an allele that pairs with or covers the X allele. The Y has no copy of these genes, so one Xb in an XY individual shows. Ask your child how many alleles an XY individual has for an X-linked gene.

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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