Cell Division
Each of us started as one cell. How do we become an organism with more than a trillion cells? In previous classes, you have learned that cells reproduce through controlled growth and division in a process called the cell cycle. All somatic cells – body cells of plants and animals – go through cell cycles. Each time a cell g oes through one complete cycle, it becomes two cells. When the cell cycle is repeated continuously, the result is a continuous production of new cells.
Do you remember the three stages of the cell cycle? What are the processes that are indicated by the letters A to G in the diagram below?
Each of us started as one cell. How do we become an organism with more than a trillion cells? In previous classes, you have learned that cells reproduce through controlled growth and division in a process called the cell cycle. All somatic cells – body cells of plants and animals – go through cell cycles. Each time a cell g oes through one complete cycle, it becomes two cells. When the cell cycle is repeated continuously, the result is a continuous production of new cells.
Do you remember the three stages of the cell cycle? What are the processes that are indicated by the letters A to G in the diagram below?
Sexual Reprod uction
When somatic cells reproduce by mitosis, the new daughter cells have the same genetic information as the parent cells. If mitosis was the only strategy for reproducing cells, we would produce exact clones of ourselves during reproduction. However, except for identical twins, no one is an exact genetic copy of another person. This is because humans reproduce through sexual reproduction, which involves two parents and leads to the production of genetically distinct offspring.
Sexual reproduction involves the fusion of a male reproductive cell with a female reproductive cell. These reproductive cells are called gametes, and the cell that results from this fusion is called a zygote. The process of combining gametes to form a zygote is called fertilization. In humans, the male gamete is the sperm cells and the female gamete is the egg cell or ovum. Gametes, which contain single, unpaired chromosomes, are said to be haploid (n). Cells that contain pairs of chromosomes, which include all somatic cells, are said to be diploid (2n).
When somatic cells reproduce by mitosis, the new daughter cells have the same genetic information as the parent cells. If mitosis was the only strategy for reproducing cells, we would produce exact clones of ourselves during reproduction. However, except for identical twins, no one is an exact genetic copy of another person. This is because humans reproduce through sexual reproduction, which involves two parents and leads to the production of genetically distinct offspring.
Sexual reproduction involves the fusion of a male reproductive cell with a female reproductive cell. These reproductive cells are called gametes, and the cell that results from this fusion is called a zygote. The process of combining gametes to form a zygote is called fertilization. In humans, the male gamete is the sperm cells and the female gamete is the egg cell or ovum. Gametes, which contain single, unpaired chromosomes, are said to be haploid (n). Cells that contain pairs of chromosomes, which include all somatic cells, are said to be diploid (2n).
The process that produces gametes with a haploid number of chromosomes is called meiosis.
So, what is meiosis?
In the following videos, you will learn about meiosis as a type of cell division involved in sexual reproduction and the stages of meiosis, specifically how a diploid germ line cell divides into four haploid gametes. You will also get to observe and identify the various stages of meiosis under a microscope.
Instructions: Please read over the following questions before you begin to watch the videos. You may want to write down some notes during the video to help you answer the questions afterwards. Post your responses to the questions in the comment section!
So, what is meiosis?
In the following videos, you will learn about meiosis as a type of cell division involved in sexual reproduction and the stages of meiosis, specifically how a diploid germ line cell divides into four haploid gametes. You will also get to observe and identify the various stages of meiosis under a microscope.
Instructions: Please read over the following questions before you begin to watch the videos. You may want to write down some notes during the video to help you answer the questions afterwards. Post your responses to the questions in the comment section!
Video #1 - Questions:
1. What are germ line cells?
2. Differentiate between the terms diploid and haploid.
3. Synapsis is the side-by-side alignment of:
a. sister chromatids of a chromosomes
b. homologous chromosomes
c. non-homologous chromosomes
d. spindle fibres
e. nuclei prior to the division of the cytoplasm
4. What is recombination (crossing over) and when does it occur?
5. At the end of meiosis I, each daughter cell is:
a. diploid, and each chromosome consists of a single chromatid
b. diploid, and each chromosome consists of two chromatids
c. haploid, and each chromosome consists of a single chromatid
d. haploid, and each chromosome consists of two chromatids
e. haploid, containing a mixture of single- and double-chromatid chromosomes
6. If the number of chromosomes were not reduced during meiosis, how many chromosomes would a human gamete have? How many chromosomes would result after fertilization?
7. What are some similarities between mitosis and meiosis II? What is the significant difference between them?
1. What are germ line cells?
2. Differentiate between the terms diploid and haploid.
3. Synapsis is the side-by-side alignment of:
a. sister chromatids of a chromosomes
b. homologous chromosomes
c. non-homologous chromosomes
d. spindle fibres
e. nuclei prior to the division of the cytoplasm
4. What is recombination (crossing over) and when does it occur?
5. At the end of meiosis I, each daughter cell is:
a. diploid, and each chromosome consists of a single chromatid
b. diploid, and each chromosome consists of two chromatids
c. haploid, and each chromosome consists of a single chromatid
d. haploid, and each chromosome consists of two chromatids
e. haploid, containing a mixture of single- and double-chromatid chromosomes
6. If the number of chromosomes were not reduced during meiosis, how many chromosomes would a human gamete have? How many chromosomes would result after fertilization?
7. What are some similarities between mitosis and meiosis II? What is the significant difference between them?
Video #2 – Questions:
8. Were you able to see all of the phases of meiosis? If not, why do you think you could not see any cells in that phase?
9. Which phase of cells was found most frequently? What can you infer, therefore, about the length of that phase?
10. During which phase(s) are chromosomes most easily identified? Explain why.
Review Questions:
11. List the phases of meiosis and an identifying feature of each phase. (If you like you can draw a diagram of each stage too!)
12. The somatic cells in a horse have 64 chromosomes.
a. What is the diploid number for a horse?
b. What is the haploid number for a horse?
c. How many chromosomes are present in a normal gamete?
d. How many chromosomes are present in a cell at prophase I?
8. Were you able to see all of the phases of meiosis? If not, why do you think you could not see any cells in that phase?
9. Which phase of cells was found most frequently? What can you infer, therefore, about the length of that phase?
10. During which phase(s) are chromosomes most easily identified? Explain why.
Review Questions:
11. List the phases of meiosis and an identifying feature of each phase. (If you like you can draw a diagram of each stage too!)
12. The somatic cells in a horse have 64 chromosomes.
a. What is the diploid number for a horse?
b. What is the haploid number for a horse?
c. How many chromosomes are present in a normal gamete?
d. How many chromosomes are present in a cell at prophase I?