Unit 5: Topic 1 - Meiosis

Question 1

What is the process used by sexually-reproducing diploid organisms to create gametes?
A) Mitosis
B) Meiosis
C) Cleavage
D) Haplosis

Answer 1

B) Meiosis

Question 2

How does meiosis ensure that sexually reproducing organisms have haploid gametes?

Answer 2

Through two rounds of division (meiosis I and meiosis II), the process of meiosis ensures that the 4 daughter cells have half the number of chromosomes that the diploid somatic cells have. During anaphase I, the homologous pairs of chromosomes (chromosomes that have the same genes in the same location, with one chromosome typically being inherited from each parent) get separated into two daughter cells. Each chromosome from the homologous pair has previously replicated, so while the 2 daughter cells are haploid, each chromosome is still duplicated. During anaphase II, the sister chromatids are separated (in each of those two cells), so the end result is 4 haploid daughter cells.

Question 3

List and explain the steps of meiosis.

Answer 3

1. Interphase: Chromosomes replicate, and the spindle fibers start forming from the centrioles
2. Prophase I: Homologous chromosomes pair up, and crossing over occurs (will be explained in the next topic); the nuclear membrane dissolves
3. Metaphase I: Homologous chromosome pairs line up in the center of the cell
4. Anaphase I: Spindle fibers attach to the homologous chromosomes, and the pairs are separated
5. Telophase I: The cell pinches inwards, and two haploid daughter cells (with duplicated chromosomes) are formed
   The following steps occur for both of the daughter cells produced at the end of meiosis I:
6. Prophase II: Nuclear membrane dissolves, and spindle fibers reform
7. Metaphase II: The chromosomes line up in the center of the cell
8. Anaphase II: The sister chromatids are separated
9. Telophase II: The cells pinch inward, and a total of 4 haploid daughter cells are formed

A diagram depicting the process of meiosis

Question 4

Explain the similarities and differences between mitosis and meiosis.

Answer 4

Similarities:
- Both start with a diploid parent cell
- Both separate sister chromatids at some point (this happens in anaphase of mitosis and anaphase II of meiosis)
- Both separate chromosomes using the same method (chromosomes line up in the center and are pulled apart by spindle fibers)

Differences:
- The two processes result in a different number of cells (mitosis produces 2 daughter cells, while meiosis produces 4)
- The daughter cells have different ploidy (mitosis results in diploid cells, while meiosis results in haploid cells)
- The genetic content of the daughter cells is different (in mitosis, the genetic content of the daughter cells is the same as the parent cell, while in meiosis, the genetic content of the daughter cells is different from the parent cell due to crossing over)