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?

   • 2 chromosomes, one from pair 1 and one from pair 2
   • 3 chromosomes, both of pair 1 and one of pair 2
   • 2 chromosomes, both members of pair 1, which are dark and light
   • 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 4, and each new sperm cell has 2
   • The zygote has 8, and each new sperm cell has 4
   • The zygote has 16, because the two cells double

4. 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.

5. 3.

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

   • 2 units
   • 8 units
   • 4 units
   • 16 units

6. Table (fruit fly real, others model data)

   Chromosome counts, columns species, body cell and sperm cell. Row: fruit fly, 8 in a body cell, 4 in a sperm cell. Row: model plant A, 12 in a body cell, 6 in a sperm cell. Row: model animal B, ? in a body cell, 15 in a sperm cell.

7. 4.

   Kira fills in a table of chromosome counts. The fruit fly row is real, and the other rows are model data. What belongs in the blank?

   • 7 chromosomes
   • 15 chromosomes
   • 60 chromosomes
   • 30 chromosomes
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?

   • R, S, P, Q
   • Q, S, P, R
   • Q, P, S, R
   • P, Q, 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 1: a body cell should have 23 chromosomes
    • Line 4: the new cell should hold one set, not two

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 4: the 4 cells should be identical copies of each other
    • Line 1: the DNA is copied twice, once for each division
    • Line 3: each finished cell has 4 chromosomes, half of 8
    • 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
    • Yes: the DNA copy splits the chromosomes as soon as it is made
    • No: the sister chromatids stay joined, and the matching pairs part in the second division
    • 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?

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

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