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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

NameDate

Circle the best answer.

  1. Ari fills an empty Punnett square for model parents XBXb and XBY. Which statement about the offspring is true?

    • No XY offspring have the trait, because the X comes from the XY parent
    • Half of the offspring have the trait, in both XX and XY
    • Half of the XY offspring have the trait, and no XX offspring do
    • Half of the XX offspring have the trait, and no XY offspring do

  2. Bo fills an empty square for the X-linked eye color that Morgan studied in fruit flies, using model genotypes XWXw and XwY. Which list gives the eye colors?

    • 1 red-eyed female : 1 white-eyed female : 1 red-eyed male : 1 white-eyed male
    • 2 red-eyed females : 1 red-eyed male : 1 white-eyed male
    • 3 red-eyed flies : 1 white-eyed fly
    • 2 red-eyed females : 2 white-eyed males

  3. Esme fills an empty square for model parents XBXB and XbY. Which statement is true?

    • No offspring have the trait, but the XX offspring are carriers
    • The XX offspring have the trait, since the XY parent has it
    • Half of the offspring have the trait and half are carriers
    • The XY offspring have the trait, because the X comes from the XY parent

  4. Read this first

    Model group of XY individuals, Northern European ancestry (model counts; rate from NIH MedlinePlus Genetics)

    groupnumber in model groupabout how many have the red-green color vision difference
    XY individuals1,2001 in 12

  5. Kira reads a model group of 1,200 XY individuals. About how many are expected to have the red-green color vision difference?

    • 100 individuals
    • 6 individuals
    • 14,400 individuals
    • 1,188 individuals

  6. Two model groups, Northern European ancestry (model counts; rates from NIH MedlinePlus Genetics)

    groupnumber in model grouprate with the red-green color vision difference
    XY individuals (men)2,4001 in 12
    XX individuals (women)2,4001 in 200

  7. Luz reads two model groups. About how many more XY than XX individuals are expected to have the trait?

    • 0 more
    • 2,388 more
    • 212 more
    • 188 more

  8. Model offspring card (model)

    itemdetail
    offspringXbY
    parent 1an XX individual
    parent 2an XY individual

  9. Noah reads a model offspring card. From which parent did the XbY offspring receive its Xb allele?

    • From either parent, because both parents pass on an X
    • From both parents, because the trait needs two Xb alleles
    • From the XX parent, because the XY parent passes on a Y
    • From the XY parent, because an XY offspring takes its X from the XY parent

  10. Genotype list (model)

    genotypechromosomes
    XBXBXX
    XBXbXX
    XbXbXX
    XBYXY
    XbYXY. XB is dominant to Xb

  11. Pia reads a genotype list. Which choice holds every genotype that shows the red-green color vision difference?

    • XbXb and XbY
    • XBXb, XbXb and XbY
    • XbXb (the Y covers the Xb allele in XbY)
    • XbY and XBY (both XY genotypes)

  12. Use this

    a circle with no dot is not marked either way.

  14. Ren reads a made-up pedigree. II-2 is a filled square. From which parent did II-2 receive the Xb allele?

    • From both I-1 and I-2 (the trait needs two Xb alleles)
    • From I-1 (an XY child takes its X from the XY parent)
    • From I-2 (an XY child takes its X from the XX parent)
    • From neither, since neither parent has the trait

  15. Tala reads the same pedigree. II-1 is a circle with no dot, so II-1 is not marked either way. What is the chance that II-1 carries Xb?

    Use the picture in question 8.

    • 1 in 1
    • 0
    • 1 in 4
    • 1 in 2

  16. 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).

  17. Zee reads a made-up pedigree. II-1 is a filled circle. Which statement fits the pedigree?

    • II-1 has one Xb allele, and one is enough to show the trait
    • II-1 has two Xb alleles, and both came from I-2
    • II-1 has two Xb alleles: one from I-1 and one from I-2
    • II-1 is a carrier, since a filled circle marks a carrier
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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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