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.
- http://bit.ly/1dOJ5JN – Click on step-through to navigate meiosis.
- (http://www.sumanasinc.com/webcontent/animations/content/meiosis.html)
![](https://blogs.ubc.ca/mrpletsch/files/2017/03/Screen-Shot-2019-07-10-at-1.07.55-PM-1024x635.png)
![](https://blogs.ubc.ca/mrpletsch/files/2017/03/Screen-Shot-2019-07-10-at-1.08.02-PM-1024x626.png)
Additional resource:
http://www.johnkyrk.com/meiosis.html
Characteristics unique to meiosis:
- Crossing over: During prophase I, there is an exchange of genetic material.
- 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
![](https://blogs.ubc.ca/mrpletsch/files/2017/03/mei1-1024x327.png)
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.
![](https://blogs.ubc.ca/mrpletsch/files/2017/03/mei2-1024x608.png)
Summer School July 10th Homework
Answer the six questions below to the best of your ability. Due Thursday, July 11th
- State the function of meiosis. [1]
- How do meiosis and mitosis differ? [2]
- Explain why meiosis is described as a reduction division. [1]
- Outline the processes that occur during the first division of meiosis. [3]
- Explain how meiosis results in genetic variation in gametes. [2]
- 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.
![](https://blogs.ubc.ca/mrpletsch/files/2017/03/mei3-1024x729.png)
Summer School July 10th Homework
Answer the six questions below to the best of your ability. Due Wednesday March 8th.
- State the function of meiosis. [1]
- State the definition of the term homologous chromosome. [1]
- Explain why meiosis is described as a reduction division. [1]
- Outline the processes that occur during the first division of meiosis. [6]
- Explain how meiosis results in genetic variation in gametes. [2]
- Outline how sexual reproduction leads to even further genetic variation within a species. [2]
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