Meiosis: How the sex cells are produced
Reading
OpenStax book: Ch. 7 - "The cellular basis of inheritance"
BJU: Section 5.3 - "Meiosis"
AP students additional reading: Princeton Review "Heredity", from Meiosis to the end.
Labs
Memo: 2020-2021 labs will include hands-on and virtual, and may vary as the Covid-19 situation changes. Some of you want more hands-on than others. We will do what we can do.
There are several good Mitosis and Meiosis labs, including:
OpenStax book: Ch. 7 - "The cellular basis of inheritance"
BJU: Section 5.3 - "Meiosis"
AP students additional reading: Princeton Review "Heredity", from Meiosis to the end.
Labs
Memo: 2020-2021 labs will include hands-on and virtual, and may vary as the Covid-19 situation changes. Some of you want more hands-on than others. We will do what we can do.
There are several good Mitosis and Meiosis labs, including:
- Mitosis lab with HeLa Case Study (fulfills AP "dirty dozen lab" #7)
- HHMI - The Eukaryotic Cell Cycle and Cancer (has both 'regular' and 'AP' lab reports)
- Univ. of Arizona Karyotyping WebLab (have used this several years)
- Several others
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 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...
| Lecture Slides: Cell Cycle - Meiosis.pptx |
Below: we will look at some videos explaining meiosis....
LABS & HOMEWORK BELOW: There are numerous labs, projects, presentations, and homework exercises posted on this portal. Don't panic. Some of these are current, some are left over from prior years, and some are just "parked" here for future use. DO NOT WORK ON A LAB OR HOMEWORK EXERCISE unless it has been assigned in your weekly class email! Due to the 2020-2021 Covid-19 situation, I will assign labs and homework as we go along based on what we are able to do.
LABS & HOMEWORK BELOW: There are numerous labs, projects, presentations, and homework exercises posted on this portal. Don't panic. Some of these are current, some are left over from prior years, and some are just "parked" here for future use. DO NOT WORK ON A LAB OR HOMEWORK EXERCISE unless it has been assigned in your weekly class email! Due to the 2020-2021 Covid-19 situation, I will assign labs and homework as we go along based on what we are able to do.
Meiosis homework questions
| 8._meiosis_homework_questions.docx |
Class presentations today
Presentation topic: Heart and Circulatory System
Presentation topic: Heart and Circulatory System
"Heart & Circulatory System" presentation
Prepare and present an 8-10 minute PowerPoint presentation in class. You already turned in your "idea" in a previous assignment. Now you will present it to the class.
Presentation topic: "The Heart and Circulatory System".
Examples: heart disease, pacemakers, artificial hearts, blood-borne infectious diseases (HIV, hepatitis B/C), how smoking and alcohol affect the heart, recent developments in heart valves, how heart muscles work, the heart’s electrical system, cardiac tissue engineering, Sickle Cell Anemia, Leukemia, new drugs or drugs under development.
Prepare and present an 8-10 minute PowerPoint presentation in class. You already turned in your "idea" in a previous assignment. Now you will present it to the class.
Presentation topic: "The Heart and Circulatory System".
Examples: heart disease, pacemakers, artificial hearts, blood-borne infectious diseases (HIV, hepatitis B/C), how smoking and alcohol affect the heart, recent developments in heart valves, how heart muscles work, the heart’s electrical system, cardiac tissue engineering, Sickle Cell Anemia, Leukemia, new drugs or drugs under development.
Mitosis and Meiosis Lab (aligns with AP Bio lab #7) - Continued from last session
This lab exercise will be spread over 2 sessions:
This lab exercise will be spread over 2 sessions:
- Part 1: Modeling mitosis and meiosis with pipe cleaner chromosomes
- Part 2: Karyotyping simulation: You will evaluate 3 patients' case histories, complete their karyotypes, and diagnose any missing or extra chromosomes. Link to Univ. of Arizona Karyotyping Simulation
- Part 3: HeLa Cells case study. HeLa cells are cervical cancer cells isolated from a woman named Henrietta Lacks. Her cells have been cultured since 1951 and used innumerous scientific experiments. Henrietta Lacks died from her cancer not long after her cells were isolated. Lacks' cancer cells contain remnants of human papillomavirus (HPV), which we now know increases the risk of cervical cancer.