Unit 6: Meiosis: How the sex cells are produced
Reading
BJU Biology: Section 5.3 - "Meiosis"
AP: OpenStax Biology Ch. 11 "Meiosis and Sexual Reproduction"
OpenStax orange book: Ch. 7 - "The cellular basis of inheritance"
Labs
Here is a list of possible labs for this lesson. I will choose from this list when we get here.
BJU Biology: Section 5.3 - "Meiosis"
AP: OpenStax Biology Ch. 11 "Meiosis and Sexual Reproduction"
OpenStax orange book: Ch. 7 - "The cellular basis of inheritance"
Labs
Here is a list of possible labs for this lesson. I will choose from this list when we get here.
- Mitosis lab with HeLa Case Study (aligns with AP "dirty dozen lab" #7)
- HHMI - The Eukaryotic Cell Cycle and Cancer (has both 'regular' and 'AP' lab reports)
- Univ. of Arizona Karyotyping WebLab
Introduction
In the previous Unit, we studied mitosis - the process whereby somatic cells replicate and divide. Somatic cells are the cells of the body (soma = body), in other words skin cells, muscle cells, nerve cells, and so forth.
In this Unit, we will be discussing meiosis - the process whereby the sex cells (sperm and eggs) are made. The sex cells are formed in the gonads - testes in the case of male, and ovaries in the case of female. Genetically speaking, they are a special type of cell which differs from somatic cells.
The process of meiosis has enormous importance in the research of genetic disorders.
In the previous Unit, we studied mitosis - the process whereby somatic cells replicate and divide. Somatic cells are the cells of the body (soma = body), in other words skin cells, muscle cells, nerve cells, and so forth.
In this Unit, we will be discussing meiosis - the process whereby the sex cells (sperm and eggs) are made. The sex cells are formed in the gonads - testes in the case of male, and ovaries in the case of female. Genetically speaking, they are a special type of cell which differs from somatic cells.
The process of meiosis has enormous importance in the research of genetic disorders.
| Lecture Slides: Cell Cycle - Meiosis.pptx |
Lecture outline
Meiosis is the process by which the germ cells contained in the gonads manufacture the sex cells (sperm and eggs). Meiosis happens in the gonads, or reproductive organs, of all sexually-reproducing organisms.
It differs from mitosis in some key aspects:
During meiosis, a single germ cell divides twice to produce four sex cells each containing half the original amount of genetic information. The sex cells are the sperm in males, eggs in females. During meiosis one cell divides twice to form four daughter cells.
Contrast this with mitosis (covered in the previous Unit): In mitosis, a single somatic cell divides once to produce two somatic cells each having the full amount of genetic information. Somatic cells are the cells of the body.
Why can't the sperm and egg be formed using mitosis? Because they would start off each having 23 pairs of chromosomes in the case of humans, and when they united during fertilization the fertilized egg would then have 46 pairs of chromosomes - and that's twice too many! Then in the next generation they would unite again and produce a fertilized egg having 92 pairs of chromosomes!...and then 184 pairs.... and so on. The genetic material would double with each generation, and that wouldn't work.
Because of this, meiosis operates in two phases during which the number of chromosomes is first cut in half; that way during fertilization the two haploid sex cells (each containing just half the genetic material) unite to form a diploid fertilized egg containing the full amount of genetic material.
Prokaryotic organisms (think: bacteria) do not need meiosis; they replicate simply by binary fission as we learned in the previous Unit. They just copy their DNA and then divide things up 50/50 and split into two identical cells. More complex eukaryotic organisms which sexually reproduce (humans, whales, corn plants) utilize meiosis in order to maintain the correct number of chromosomes - but also to introduce genetic variety within their species. That is one of the advantages of sexual reproduction within a species - you end up with offspring which are not genetically identical - and genetic variety helps to ensure survival of the species.
Thankfully, meiosis I and II use the same terminology as mitosis: "prophase, metaphase, anaphase, and telophase". Your textbooks - and the lecture slides and videos below - cover this in greater detail...
Meiosis is the process by which the germ cells contained in the gonads manufacture the sex cells (sperm and eggs). Meiosis happens in the gonads, or reproductive organs, of all sexually-reproducing organisms.
It differs from mitosis in some key aspects:
During meiosis, a single germ cell divides twice to produce four sex cells each containing half the original amount of genetic information. The sex cells are the sperm in males, eggs in females. During meiosis one cell divides twice to form four daughter cells.
Contrast this with mitosis (covered in the previous Unit): In mitosis, a single somatic cell divides once to produce two somatic cells each having the full amount of genetic information. Somatic cells are the cells of the body.
Why can't the sperm and egg be formed using mitosis? Because they would start off each having 23 pairs of chromosomes in the case of humans, and when they united during fertilization the fertilized egg would then have 46 pairs of chromosomes - and that's twice too many! Then in the next generation they would unite again and produce a fertilized egg having 92 pairs of chromosomes!...and then 184 pairs.... and so on. The genetic material would double with each generation, and that wouldn't work.
Because of this, meiosis operates in two phases during which the number of chromosomes is first cut in half; that way during fertilization the two haploid sex cells (each containing just half the genetic material) unite to form a diploid fertilized egg containing the full amount of genetic material.
Prokaryotic organisms (think: bacteria) do not need meiosis; they replicate simply by binary fission as we learned in the previous Unit. They just copy their DNA and then divide things up 50/50 and split into two identical cells. More complex eukaryotic organisms which sexually reproduce (humans, whales, corn plants) utilize meiosis in order to maintain the correct number of chromosomes - but also to introduce genetic variety within their species. That is one of the advantages of sexual reproduction within a species - you end up with offspring which are not genetically identical - and genetic variety helps to ensure survival of the species.
Thankfully, meiosis I and II use the same terminology as mitosis: "prophase, metaphase, anaphase, and telophase". Your textbooks - and the lecture slides and videos below - cover this in greater detail...
Below: we will look at some videos explaining meiosis....
Meiosis homework questions
| 8._meiosis_questions_2021.docx |
HHMI WebLab: "The Eukaryotic Cell Cycle and Cancer"
- The WebLab is located here www.biointeractive.org/classroom-resources/eukaryotic-cell-cycle-and-cancer
- Click the "Launch Interactive" button. The interactive window will open. You will be clicking around on the interactive diagram as you answer the questions.
- Regular class: Research and respond to all questions on the "Overview Worksheet"
- AP students: Research and respond to all questions on the "In-Depth Worksheet", including the Extension Questions. (don't do the overview worksheet, above).
- Upload your completed work to Canvas.