Sex-linked traits and reading a pedigree

Grade 9 Science Worksheet - Building Confidence

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. 1.

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

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

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. 2.

   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)

   gene	location
   red-green color vision genes	X chromosome
   Y chromosome	no copy of these genes

6. 3.

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

   • Recessive inheritance (the allele is hidden)
   • X-linked inheritance (the genes sit on the X)
   • Y-linked inheritance (the genes sit on the Y)
   • Autosomal inheritance (the genes sit on a non-sex pair)
7. 4.

   Jun 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 (a typical and a difference allele)
   • XbY (a difference allele and a Y)
   • XbXb (two difference alleles)
8. 5.

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

   • XBXB (two typical alleles)
   • XbY (a difference allele and a Y)
   • XBXb (a typical and a difference allele)
   • XBY (a typical allele and a Y)
9. 6.

   Luz fills a Punnett square for model fruit flies. Which genotype goes in the blank box?

   • XwY (a white-eye allele and a Y)
   • XWY (a red-eye allele and a Y)
   • XwXw (two white-eye alleles)
   • XWXw (a red-eye and a white-eye allele)

10. 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.

11. 7.

    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
    • XX and XY individuals show it equally often anyway
    • Xb becomes dominant in an XY individual

12. 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.

13. 8.

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

14. 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. 9.

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

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

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. 10.

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

    • 5 individuals
    • 2 individuals
    • 3 individuals
    • 1 individual