Meiosis

Science 9 Biology

Lesson objectives

• Know the difference between Meiosis and mitosis

• Explain Meiosis, including the genetic advantages.

• Know the difference between haploid and diploid cells.

Somatic cells

• Somatic cells are cells that replicate through cell division.

• Human somatic cells have 23 pairs of chromosomes, for a total of 46 chromosomes.

• Somatic cells are called ‘diploid cells’ because they have the full number of chromosomes

Gametes

• The sex cells are also called gametes. • Gametes have half the chromosomes of the

parent cell so they are called ‘haploid cells.’• Male gametes = sperm• female gametes = eggs or ova (singular: ovum)

Why haploid?

• If egg and sperm cells contained all chromosomes, the offspring would have DOUBLE the genes!

• The process that produces gametes, which have half the number of chromosomes as the parent, is called meiosis.

Corresponding pairs

• Diploid (2n) somatic cells have their chromosomes arranged in corresponding pairs, called homologous chromosomes.

• The genes on one of the chromosomes in the pair correspond to the genes on the other chromosome in the pair.

• This is how you could pass on genes for blue eyes even if your eyes are brown.

• The first phase, meiosis I is similar to mitosis during interphase and prophase.

• During interphase, the chromosomes replicate to form joined sister chromatids.

• During prophase, the chromosomes shorten and thicken, and become visible with a light microscope.

• Metaphase and anaphase are different in Meiosis I.• the homologous chromosomes (each joined to its

sister chromatid) pair up along the equator. • Then, during anaphase the pairs of homologous

chromosomes separate and move to opposite poles along with their sister chromatids.

• The sister chromatids do not separate in meiosis I.

• In Meiosis II, the sister chromatids in the two daughter cells line up at the equator of the cell.

• Each chromatid is pulled to the opposite pole. The nuclear membranes reform, and cytokinesis occurs, resulting in four haploid daughter cells called gametes.

• This second phase is similar to mitosis, in which the sister chromatids separate. But since meiosis II starts with two daughter cells, which both divide in two, four daughter cells are produced. Mitosis and meiosis are compared in Table 1.

Pleistocene chromosome activity

• In groups of 3, use the Pleistocene and 3 sheets of construction paper to show how chromosomes move through all the stages of Meiosis and mitosis. **NOTE** your chromosomes should be color coded!

• One person in each group should take a photograph of each stage with their phone

• Using these photos, make a digital slide show with titles of each phase and email them to plegun@gulfislandssecondary.ca

‘What happens in Meiosis’1. Gametes,

gametes, gametes

2. Fertilization, zygote

3. Mitosis, embryo4. 235. 23, haploid

6. Chromosome7. Meiosis I8. Meiosis II9. Diploid, 4

Comparing meiosis and mitosis

1. In both, chromosomes line up along the equator

2. In meiosis I, each pair of chromosomes includes one chromosome from each parent

3. In both, chromosomes are pulled to opposite poles

4. In meiosis II, there are half as many chromosomes as in mitosis

Meiosis multiple choice…

1.C2.E3.B4.J5.H

6.I7.A8.D9.F10.C

11.C12.C13.A14.A