Keywords:

Haploid – A cell with one set on each chromosome (in Humans – 23). Sperm and Eggs.

Diploid – A cell with two sets of each chromosome (In Humans 23 chromosomes, 2 of each = 46 total). All cells except from sex cells are diploid!

Gametes – Cells involved in sexual reproduction. Four are produced from meiosis. Ex. Sperm and Eggs.

Gonads – Primary sex organs. Where meiosis occurs to produce gametes.

Homologous Chromosomes – Chromosomes that carry the same genes (DNA that codes for a trait). We get one from the mother and one from the father.

Stages of meiosis:

Crete a table showing each of the stages of meiosis 1 and 2. Use the link below, gather information about the stages of both meiosis 1 and 2. Draw each stage – be sure to include adequate detail as presented to you be the resources.

Meiosis 1: Produces 2 daughter cells with 23 chromosomes (haploid)
Meiosis 2 – Follows similar steps to mitosis, but the cells are already haploid (only 23 chromosomes)

Additional resource:

http://www.johnkyrk.com/meiosis.html

Identifying stages of Meiosis

Characteristics unique to meiosis:

  1. Crossing over: During prophase I, there is an exchange of genetic material.
  2. Pairing of homologous chromosomes: Homologous chromosomes synapse (pair up) to form bivalents.
  • NON-SISTER CHROMATIDS break at the same point, twist around each other and exchange a segment of their chromosome with each other.
  • Since genes are at the same location, but DNA may differ between maternal and paternal chromosomes, a new combo of alleles may be present when the chromosomes separate
Figure 1: Crossing over

          3. Random Orientation – During metaphase I, homologous pairs line up along the centre of the   cell. The way they line up is random (either maternal or paternal chromosome can orient to either pole).

  • This increases genetic variation in gametes – In humans, 2^23 (8,388,608) possible outcomes.
Figure 2: Random orientation of chromosomes during Metaphase 1

Summer School July 10th Homework

Answer the six questions below to the best of your ability. Due Thursday, July 11th

  1. State the function of meiosis. [1]
  2. How do meiosis and mitosis differ? [2]
  3. Explain why meiosis is described as a reduction division. [1]
  4. Outline the processes that occur during the first division of meiosis. [3]
  5. Explain how meiosis results in genetic variation in gametes. [2]
  6. Outline how sexual reproduction leads to even further genetic variation within a species. [2]

SUMMER SCHOOL – INFO BELOW IS NOT NECESSARY!

Extra or missing chromosomes

  • Non-disjunction – errors in anaphase (I or II) in which a pair of homologous chromosomes fails to separate.
  • Can lead to a gamete with an extra chromosome or missing one.
  • Ex. Klinefelter Syndrome
  • Males with an extra X chromosome (XXY)
  • ~1:1000 males

Symptoms are often not obvious, however sterility is common.

Figure 3: Non-disjunction during anaphase I and II

Summer School July 10th Homework

Answer the six questions below to the best of your ability. Due Wednesday March 8th.

  1. State the function of meiosis. [1]
  2. State the definition of the term homologous chromosome. [1]
  3. Explain why meiosis is described as a reduction division. [1]
  4. Outline the processes that occur during the first division of meiosis. [6]
  5. Explain how meiosis results in genetic variation in gametes. [2]
  6. Outline how sexual reproduction leads to even further genetic variation within a species. [2]