Meiosis: making egg and sperm cells with half the chromosomes

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. 1.

   Dark and light show which parent each chromosome came from. A model animal body cell has pair 1 and pair 2, each with one dark and one light chromosome. Ari lists what one sperm cell could hold. Which is possible?

   • 3 chromosomes, both of pair 1 and one of pair 2
   • 2 chromosomes, both members of pair 1, which are dark and light
   • 2 chromosomes, one from pair 1 and one from pair 2
   • 4 chromosomes, both members of each pair

2. Read this first

   Trace card (real fruit fly counts: body cells have 8 chromosomes)

   Egg cell, 4 chromosomes. Sperm cell, 4 chromosomes. They join to make a zygote with ? chromosomes. The fly that grows from the zygote later makes sperm cells with ? chromosomes each.

3. 2.

   A fruit fly egg cell (4 chromosomes) is joined by a sperm cell (4 chromosomes). The new fly later makes sperm cells. Bo traces the counts. Which is right?

   • The zygote has 8, and each new sperm cell has 8
   • The zygote has 16, because the two cells double
   • The zygote has 4, and each new sperm cell has 2
   • The zygote has 8, and each new sperm cell has 4

4. Count card (real count: body cells have 8 chromosomes)

   After the DNA is copied, the cell has 16 sister chromatids in all, 2 for each of its 8 chromosomes. The cell then completes meiosis. Chromatids in each finished cell: ?

5. 3.

   After its DNA is copied, a fruit fly cell has 16 sister chromatids. It completes meiosis. How many chromatids does each finished cell have, asks Esme?

   • 4 chromatids
   • 2 chromatids
   • 8 chromatids
   • 16 chromatids

6. Table (model units, model data)

   DNA amount through meiosis, columns stage, cells, DNA per cell and DNA in all cells. Row: before copying, 1 cell, 4 units per cell, 4 units in all. Row: after copying, 1 cell, 8 units per cell, 8 units in all. Row: after the first division, 2 cells, 4 units per cell, 8 units in all. Row: after the second division, 4 cells, 2 units per cell, ? units in all.

7. 4.

   Jun reads a table of model DNA amounts through meiosis. What belongs in the last blank?

   • 4 units
   • 8 units
   • 2 units
   • 16 units
8. 5.

   Luz puts four picture cards of one fruit fly cell in order, starting from a cell whose DNA is already copied. Which order is right?

   • P, Q, S, R
   • R, S, P, Q
   • Q, S, P, R
   • Q, P, S, R

9. Notebook (human counts)

   Line 1: A human body cell has 46 chromosomes. Line 2: An egg cell and a sperm cell each have 23 chromosomes. Line 3: At fertilization the two cells join, and the new cell has 92 chromosomes. Line 4: The new cell holds two sets of chromosomes, one from each cell.

10. 6.

    Noah's notebook describes fertilization using human counts. Which line has a flaw?

    • Line 3: 23 + 23 = 46, so the new cell has 46 chromosomes
    • Line 2: an egg cell should have 46 chromosomes like a body cell
    • Line 4: the new cell should hold one set, not two
    • Line 1: a body cell should have 23 chromosomes

11. Notebook (real fruit fly count)

    Line 1: A body cell with 8 chromosomes copies its DNA once. Line 2: It then divides twice in a row, making 4 cells. Line 3: Each of the 4 finished cells has 8 chromosomes. Line 4: The 4 cells can carry different combinations of alleles.

12. 7.

    Pia's notebook describes the whole of meiosis in a fruit fly cell. Which line has a flaw?

    • Line 1: the DNA is copied twice, once for each division
    • Line 3: each finished cell has 4 chromosomes, half of 8
    • Line 4: the 4 cells should be identical copies of each other
    • Line 2: one division makes 2 cells, not 4

13. Claim card (model, not to scale)

    In meiosis I, every chromosome splits into its 2 sister chromatids, which halves the chromosome number. Model cell: 4 X-shaped chromosomes in 2 matching pairs, lined up in pairs across the middle.

14. 8.

    Ren reads a claim that the first division of meiosis splits every chromosome into two sister chromatids. Which reply is best?

    • No: the matching pairs part first, and the sister chromatids part in the second division
    • No: the sister chromatids stay joined, and the matching pairs part in the second division
    • Yes: the DNA copy splits the chromosomes as soon as it is made
    • Yes: the sister chromatids part in the first division, which halves the number

15. Claim card (human counts)

    a human body cell has 46 chromosomes. Suppose an egg cell with 46 chromosomes and a sperm cell with 46 chromosomes joined. The claim says the chromosome number would grow with each generation.

16. 9.

    Tala reads a claim: if egg and sperm cells had the body-cell count, the number would keep growing. Which reply is best?

    • True: but the number would rise once, to 92, and then stay there
    • True: 46 + 46 = 92 in the new cell, and it would keep rising, so gametes must carry half
    • False: joining cells would not add chromosomes, so the new cell keeps 46
    • False: normal fertilization already takes the number from 46 to 92 and back

17. Claim card (model)

    A fruit fly body cell with 8 chromosomes completes meiosis and makes 4 finished cells, each with 4 chromosomes. The claim says the 4 cells are identical to each other.

18. 10.

    Zee reads a claim that the four cells made in one meiosis are identical. Which reply is best?

    • No: each has 4 chromosomes, but which pair member each gets can differ
    • No: they differ in how many chromosomes each one holds, as cells divide unevenly
    • Yes: they have the same number of chromosomes, so their alleles must match
    • Yes: they came from one cell, so they are exact copies of one another