Meiosis: making egg and sperm cells with half the chromosomes
Grade 9 Science Worksheet - Challenge Me
Circle the best answer.
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
- 4 chromosomes, both members of each pair
- 2 chromosomes, both members of pair 1, which are dark and light
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.
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 4
- 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 8
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.
Jun reads a table of model DNA amounts through meiosis. What belongs in the last blank?
- 16 units
- 2 units
- 4 units
- 8 units
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.
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?
- 60 chromosomes
- 30 chromosomes
- 7 chromosomes
- 15 chromosomes
Notebook (real fruit fly count, steps are the standard model)
Line 1: A body cell with 8 chromosomes copies its DNA once, so each chromosome has 2 sister chromatids. Line 2: In the first division the 4 matching pairs part, so each cell gets 4 X-shaped chromosomes. Line 3: In the second division the matching pairs part again, leaving 2 chromosomes in each cell. Line 4: The 4 finished cells each hold 4 single chromosomes.
Milo's notebook describes meiosis in a fruit fly cell. Which line has a flaw?
- Line 4: four cells should hold 8 chromosomes each
- Line 3: the sister chromatids part, leaving 4 chromosomes in each cell
- Line 2: the first division should split the sister chromatids
- Line 1: the DNA should be copied before each division
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.
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
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.
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
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.
Ren reads a claim that the first division of meiosis splits every chromosome into two sister chromatids. Which reply is best?
- 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
- No: the matching pairs part first, and the sister chromatids part in the second division
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.
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
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.
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
- Yes: they have the same number of chromosomes, so their alleles must match
- 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