Sex-linked traits and reading a pedigree

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. 1.

   Ari crosses model parents XBXb and XbY. What is the chance that one offspring is an XX individual with the trait?

   • 1 in 2
   • 0
   • 3 in 4
   • 1 in 4
2. 2.

   Bo crosses model fruit flies XwXw and XWY. What is the chance that one offspring is a white-eyed XY fly?

   • 1 in 4
   • 3 in 4
   • 1 in 2
   • 0
3. 3.

   Esme crosses model parents XBXb and XBY. One offspring is an XY individual. What is the chance that it has the trait?

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

4. Read this first

   Use this

   Pedigree of a made-up family for a made-up trait (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).

5. 4.

   Jun reads a made-up pedigree. Neither parent has the trait, but daughter II-1 does. Which choice states what this rules out?

   • Both patterns: a parent without the trait has no allele
   • X-linked recessive: the XY parent would have the trait too
   • Neither pattern: an XX parent can pass Xb to a daughter
   • Autosomal recessive: parents without the trait cannot carry it

6. 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.

7. 5.

   Luz reads a made-up pedigree. The trait appears in I-1 and III-1 but skips II-1. Which statement explains it?

   • I-1 passed Xb to II-1 on a Y chromosome
   • III-1 got its Xb from II-2, the XY parent
   • II-1 is a carrier of Xb from I-1
   • II-1 has the trait, but it is hidden

8. Notebook

   Notes on a model cross (classmate's notebook), 4 lines. Columns: line, entry. Line 1: A model cross has parents XBXb and XBY. Line 2: XX offspring get one X from each parent. Line 3: XY offspring get their X from the XY parent. Line 4: So the XbY box is one of the four boxes.

9. 6.

   Milo reads a classmate's notebook about a model XBXb × XBY cross. Which line has the mistake?

   • Line 2: XX offspring should get both X chromosomes from one parent
   • Line 3: an XY offspring gets its X from the XX parent
   • Line 1: the XY parent should be written XbY
   • Line 4: XbY should be a carrier, because the Y holds a second allele

10. Notebook

    Notes on pedigree symbols (classmate's notebook), 4 lines. Columns: line, entry. Line 1: Squares are XY individuals and circles are XX individuals. Line 2: A filled symbol is an individual with the trait. Line 3: A circle with a dot is a carrier, and it does not show the trait. Line 4: An XY individual with one Xb allele is a carrier.

11. 7.

    Pia reads a classmate's notebook about pedigree symbols. Which line has the mistake?

    • Line 1: squares should be XX individuals
    • Line 4: an XY individual with one Xb allele has the trait
    • Line 2: a filled symbol should mean a carrier
    • Line 3: a circle with a dot should show the trait

12. Model offspring card (model)

    item	detail
    offspring	XbY
    parent 1	an XX individual with genotype XBXb
    parent 2	an XY individual with genotype XBY

13. 8.

    Ren claims that the XbY offspring must have received its Xb from the XY parent. Do you agree?

    • Yes, because the XY parent passes an X to each child
    • No, because the XY parent passes on a Y, so the Xb came from the XX parent
    • Yes, because the XX parent has typical color vision and holds no Xb
    • No, because the Xb came from the Y of the XY parent

14. Red-green color vision difference, Northern European ancestry (data: NIH MedlinePlus Genetics)

    group	about how many have it
    men (XY individuals)	1 in 12
    women (XX individuals)	1 in 200

15. 9.

    Tala claims that the trait should be about as common in XX as in XY individuals, because the genes sit on the X. Do you agree?

    • Yes, because both XX and XY individuals carry X chromosomes
    • No, because one Xb shows in XY, but an XX individual needs two
    • No, because the Y holds a second copy of Xb in XY individuals
    • Yes, because an XX individual with one Xb also shows the trait
16. 10.

    Zee claims that II-2, a circle with no dot, cannot pass an Xb allele to a child. Do you agree?

    • No, because II-2 got a Y chromosome that holds Xb
    • No, because II-2 got an Xb from I-1 and can pass it on
    • Yes, because a symbol that is not filled holds no Xb allele
    • Yes, because a carrier would show the trait