Amoeba proteus– Reproduction
As Amoeba proteus is a type of amoeba, it reproduces asexually through binary fission. Binary fission is where an individual cell (the parent cell) duplicates itself and divides into two new daughter cells through the process of mitosis. The steps involved in the process of binary fission are as follows:
1. The DNA of the amoeba uncoils, and the chromosome is replicated.
2. The amoeba grows in size, and the two sister chromatids migrate to the opposite poles of the cell.
3. The amoeba elongates, the chromosomes are separated, and a cleavage furrow forms in the middle.
4. The cell splits in the middle, forming two identical daughter cells, (a new cell wall is also formed in order to facilitate this.)
One advantage of binary fission as a means of reproduction is that the process is very rapid compared to forms of sexual reproduction. For example, E. coli. (Escherichia coli) divides every 20 minutes. One disadvantage, however, is that because all daughter cells are identical, the species can quickly become vulnerable to external influences. For example, when antibiotics are developed. If an antibiotic were developed against Amoeba proteus, all cells would be vulnerable until one cell duplicates with a random DNA mutation making it immune. This immune amoeba would duplicate until, eventually, the species as a whole is immune to the antibiotic.
Brown rat (Rattus norvegicus)
The brown rat, on the other hand, reproduces sexually, meaning they require two partners to do so. Once they reach sexual maturity at around 11 weeks, they can reproduce all year round provided the female is in oestrus (when she is sexually receptive after ovulation.) Rats have a life expectancy of 1 year on average, in which a female usually has 3-5 litters of 7-8 pups at one time (Davis, 1953). In terms of mating habits, the brown rat is polygamous- females frequently switch partners to ensure pregnancy. Mating is initiated when a male sniffs a female to show interest. If the female is not in oestrus, she will kick the male to indicate this. However, if she is in oestrus, the two will wiggle their ears at one another to show interest. Finally, the male rat will mount the female and insert the penis into the vagina until ejaculation occurs, multiple times consecutively to ensure pregnancy (Hull, Dominguez, 2007.)
On a more biological level, as the brown rat reproduces sexually, its offspring go through meiosis rather than mitosis. Meiosis ensures that the offspring produced are genetically varied to its parents. One diploid cell (42 chromosomes) will divide twice, forming four haploid (21 chromosomes) daughter cells. These will be either the egg cells in the female rat or the sperm cells
in the male rat. During meiosis, the gametes that are being produced undergo different steps to ensure genetic variation. One of these is crossing over. This is when two sister chromatids overlap each other and swap small sections of DNA with each other. Another way in which genetic variation is achieved is through ransom fertilisation, meaning it is down to chance which sperm will be the one to successfully fertilise the egg. When fertilisation occurs, these haploid cells will combine to create a diploid zygote.
Comparison:
The way in which Amoeba proteus and Rattus norvegicus reproduce is very different. For example, Amoeba proteus reproduce asexually through binary fission, and the brown rat reproduces sexually. This means that the amoeba does not need any others of its species in order to reproduce whereas the brown rat needs another partner to do so. Therefore, offspring of Amoeba proteus will be genetically identical, and offspring of the brown rat will be genetically varied.