Learning Outcome
Understand that the continuity of life requires:
- the replication of genetic material, and
- its transfer to the next generation through processes, including binary fission, mitosis, meiosis and fertilisation (SU)
1. Replicating genetic material
- This takes place via the DNA replication process discussed in previous lessons.
- Without replication, new cells would have no code for cellular processes, there would be no further life.
2. Transfering genetic material to the next generation
Via Binary Fission
In the process of binary fission, an organism duplicates its genetic material (DNA), and then divides into two parts (cytokinesis), with each new organism receiving one copy of DNA.
Binary fission is the primary method of reproduction of prokaryotic organisms.
It is an asexual method of reproduction as it does not require another individual.
When replication is complete, a dividing line—called a septum—forms, physically separating the cytoplasm of the cells. A cell wall then forms along the septum and the cell pinches in two, forming the daughter cells.
Information from: https://www.britannica.com › science › binary-fission and https://www.thoughtco.com/binary-fission-vs-mitosis-similarities-and-differences-4170307
In the process of binary fission, an organism duplicates its genetic material (DNA), and then divides into two parts (cytokinesis), with each new organism receiving one copy of DNA.
Binary fission is the primary method of reproduction of prokaryotic organisms.
It is an asexual method of reproduction as it does not require another individual.
When replication is complete, a dividing line—called a septum—forms, physically separating the cytoplasm of the cells. A cell wall then forms along the septum and the cell pinches in two, forming the daughter cells.
Information from: https://www.britannica.com › science › binary-fission and https://www.thoughtco.com/binary-fission-vs-mitosis-similarities-and-differences-4170307
Via Mitosis
Where a single cell divides into two identical daughter cells (cell division). During mitosis one cell divides once to form two identical cells. The major purpose of mitosis is for growth and to replace worn out cells. Mitosis is divided into five phases: 1. Interphase 2. Prophase 3. Metaphase 4. Anaphase 5. Telophase & Cytokinesis |
Wait...Why the different names for Binary Fission & Mitosis?
They are different!!
While, binary fission and mitosis are both types of asexual reproduction in which the parent cell divides to form two identical daughter cells, fission primarily occurs in prokaryotes (bacteria), while mitosis occurs in eukaryotes (e.g., plant and animal cells).
Another way to look at it is that in binary fission the cell that divides lacks a nucleus, while in mitosis, the cell that divides does possess a nucleus. As a result, there are a number of differences in the process of dividing these different cell types.
To get a better understanding of the processes, let's take a closer look at what's involved.
While, binary fission and mitosis are both types of asexual reproduction in which the parent cell divides to form two identical daughter cells, fission primarily occurs in prokaryotes (bacteria), while mitosis occurs in eukaryotes (e.g., plant and animal cells).
Another way to look at it is that in binary fission the cell that divides lacks a nucleus, while in mitosis, the cell that divides does possess a nucleus. As a result, there are a number of differences in the process of dividing these different cell types.
To get a better understanding of the processes, let's take a closer look at what's involved.
Via Meiosis & Fertilisation
Meiosis has two major phases:
Meiosis has two major phases:
- Meiosis I divides 4n germ cells (primary gametocytes) to form 2n intermediate cells (secondary gametocytes).
- Meiosis II divides 2n cells to form n (haploid) gametes.
Meiosis I:
A brief period of interphase occurs before Meiosis II
Meiosis II:
Daughter cells have only single chromatids from each bivalent and are thus haploid (n). These are now gametes ready for fertilisation to restore diploidy (2n).
- Prophase I – Chromosomes condense and in synapsis, homologous chromosomes pair up as bivalents
- Metaphase I – The nuclear envelope dissolves and bivalents assemble at the cell’s equator
- Anaphase I – Disjunction is the separation of bivalents when maternal and paternal chromosomes move to opposite poles of the cell
- Telophase I – Spindle fibres that have segregated the bivalents dissolve, the chromosomes de-condense and cytokinesis occurs
A brief period of interphase occurs before Meiosis II
Meiosis II:
- Prophase II – A new spindle forms at right angles to the first
- Metaphase II – Chromosomes move to the equator of the spindle
- Anaphase II – Chromatids separate and move to opposite ends of the cell
- Telophase II – Spindle apparatus dissolves, nuclear membrane reappears and cytokinesis occurs
Daughter cells have only single chromatids from each bivalent and are thus haploid (n). These are now gametes ready for fertilisation to restore diploidy (2n).
Fertilisation
Now you should:
- Read the entire Chapter 2 (if you haven't already).
- Complete Question Sets 2.2 and 2.3.
- Complete Activity Sheet on Seqta called "Mitosis".
- Control of the Cell Cycle Game:https://educationalgames.nobelprize.org/educational/medicine/2001/about.html