Pretest

Question 1 • CMS 2026-2027 Biology CREDIT RECOVERY

Drosophila eye color is an X-linked trait. Red eye color is dominant, and white eye color is recessive. Which Punnett square shows a cross in which the probability of offspring will have red eyes is 100 percent?

Answer

Image with description 2 by 2 Punnett square. Columns labeled X superscript lowercase r and Y. Rows labeled X superscript uppercase R and X superscript lowercase r. Cells show X superscript uppercase R X superscript lowercase r, X superscript uppercase R Y, X superscript lowercase r X superscript lowercase r, and X superscript lowercase r Y.

Image with description 2 by 2 Punnett square. Columns labeled X superscript lowercase r and Y. Rows labeled X superscript lowercase r and X superscript lowercase r. Cells show X superscript lowercase r X superscript lowercase r, X superscript lowercase r Y, X superscript lowercase r X superscript lowercase r, and X superscript lowercase r Y.

Image with description 2 by 2 Punnett square. Columns labeled X superscript lowercase r and Y. Rows labeled X superscript uppercase R and X superscript uppercase R. Cells show X superscript uppercase R X superscript lowercase r, X superscript uppercase R Y, X superscript uppercase R X superscript lowercase r, and X superscript uppercase R Y.

Image with description 2 by 2 Punnett square. Columns labeled X superscript uppercase R and Y. Rows labeled X superscript uppercase R and X superscript lowercase r. Cells show X superscript uppercase R X superscript uppercase R, X superscript uppercase R Y, X superscript uppercase R X superscript lowercase r, and X superscript lowercase r Y.

Image with description A Punnett square is shown. The columns are labeled Upper X r and Upper Y. The rows are labeled x Upper R and x r. Clockwise, from top-left, the boxes include: Upper X Upper R Upper X r, Upper X Upper R Y, Upper X r Upper Y, Upper X r Upper X r.

Explanation

Choice C pairs a mother with two red-eye alleles (XᴿXᴿ) with a white-eye father (XʳY). Every daughter inherits Xʳ from her father and Xᴿ from her mother, making her XᴿXʳ; every son inherits Y from his father and Xᴿ from his mother, making him XᴿY. Since each offspring has the dominant red-eye allele, all offspring will have red eyes.

AI-written and checked against the verified answer.

More from this Course

Pretest

Pretest

Pretest