Meiosis: making egg and sperm cells with half the chromosomes

Grade 9 Science Worksheet

Circle the best answer.

1. Read this first

   Meiosis in a fruit fly, counts per cell (real body-cell count, standard steps)

   stage	cells	chromosomes per cell	chromatids per cell
   before copying	1 cell	8 chromosomes	8 chromatids
   after copying	1 cell	8 chromosomes	16 chromatids
   after the first division	2 cells	? chromosomes	? chromatids
   after the second division	4 cells	4 chromosomes	4 chromatids

2. 1.

   Bo fills in the table for a fruit fly cell. What belongs in the blanks for one cell after the first division?

   • 8 chromosomes, 16 chromatids
   • 4 chromosomes, 8 chromatids
   • 8 chromosomes, 8 chromatids
   • 4 chromosomes, 4 chromatids
3. 2.

   a fruit fly body cell has 8 chromosomes and completes meiosis. Total chromosomes in all the finished cells together: ? A fruit fly body cell (8 chromosomes) completes meiosis. Esme adds up the chromosomes in all the finished cells together. What is the total?

   • 32 chromosomes
   • 8 chromosomes
   • 4 chromosomes
   • 16 chromosomes
4. 3.

   Kira reads cell U, one of the two cells made by the first division of a fruit fly cell. What happens to its chromosomes in the second division?

   • Matching partners part, with 2 chromosomes going to each end
   • The 4 X shapes copy their DNA again and then part
   • Each X splits into 2 chromatids, with 4 going to each end
   • Each X stays whole, with 2 X shapes going to each end

5. Count card (real count)

   The starting cell has 8 chromosomes. Each cell after the first division has 4 chromosomes, and each of those is still 2 sister chromatids joined. Each cell after the second division has 4 chromosomes.

6. 4.

   Luz asks which division lowers a fruit fly cell's count from 8 chromosomes to 4, and why. Which statement is best?

   • The second, because the sister chromatids go to different cells
   • The first, because the DNA is copied then
   • The first, because the matching chromosomes go to different cells
   • The second, because each cell divides again

7. Count card (human counts)

   Egg cell, 23 chromosomes. Sperm cell, 23 chromosomes. The two cells join to make a new cell (a zygote) with ? chromosomes.

8. 5.

   An egg cell and a sperm cell each have 23 chromosomes and join in fertilization. Which description of the new cell does Milo choose?

   • 92 chromosomes, in 46 matching pairs
   • 23 chromosomes, one set from the egg cell
   • 46 chromosomes, with the egg cell supplying the whole set
   • 46 chromosomes, in 23 matching pairs

9. Count card (model data, a model plant)

   The new cell formed at fertilization has 10 chromosomes in matching pairs. Chromosomes from the pollen cell: ? Chromosomes from the egg cell: ?

10. 6.

    A model plant's new cell has 10 chromosomes after a pollen cell and an egg cell join. Noah traces where they came from. Which is right?

    • 10 from the egg cell, which holds the full set
    • 4 from the pollen cell and 6 from the egg cell
    • 5 from the pollen cell and 5 from the egg cell
    • 10 from the pollen cell and 10 from the egg cell

11. Table (model data)

    Chromosomes per cell across two generations, columns cell and chromosomes. Row: parent 1 body cell, 12. Row: parent 1 sperm cell, 6. Row: parent 2 body cell, 12. Row: parent 2 egg cell, 6. Row: offspring zygote, 12. Row: offspring sperm cell, ?

12. 7.

    Pia fills in a table that follows chromosome counts for a model animal across two generations. What belongs in the last row?

    • 24 chromosomes
    • 6 chromosomes
    • 12 chromosomes
    • 18 chromosomes

13. Chromosome cards (model, pairs 1 and 2 are different chromosome pairs)

    The parent cell holds 4 cards. Pair 1: a card with A and a card with a. Pair 2: a card with B and a card with b.

14. 8.

    A parent cell has chromosome pair 1 with alleles A and a, and pair 2 with B and b. Ren deals the cards for one egg cell. Which cards can go to it?

    • A, a and B
    • A and a
    • Aa and Bb
    • A and b

15. Use this

    Pair 1 and pair 2 are different chromosome pairs. The parent cell has pair 1 with A and a, and pair 2 with B and b. Side edge, from the other parent (same alleles): AB, Ab, aB, ab. Top edge: ?

16. 9.

    Tala deals cards along the top edge of a Punnett grid. The parent cell has A and a on pair 1, and B and b on pair 2. Which cards go on the edge?

    • A, a, B, b as single cards
    • AB and ab
    • AB, Ab, aB, ab
    • Aa and Bb
17. 10.

    Zee fills one box of a Punnett grid. The top card is Ab and the side card is aB. Which genotype goes in the box?

    • Aabb (A: one capital, one small; B: two small)
    • AaBb (A: one capital, one small; B: one capital, one small)
    • aaBb (A: two small; B: one capital, one small)
    • AABB (A: two capital; B: two capital)