Diagrammatically distingnish between mitosis and meiosis in animal cells
In which cells does meiosis occur in the plants?
Answers
Answer:
Explanation:
Mitosis
Meiosis
What is the purpose of this process?
In a unicellular organism, the purpose of mitosis is to proliferate asa species. In a multicellular organism, the purpose can be to grow during development, or to repair or regenerate
adamaged tissue, for example.
To create gametes with only one copy of the organism’s genetic information, in preparation for sexual reproduction. Various steps in meiosis create opportunity for genetic diversity in the daughter cells. This is the raw substrate for evolution.
What is the outcome of this process?
Two diploid cells with identical genetic information.
Four haploid cells with different genetic information.
Which organisms perform this process?
Mitosis is performed by unicellular and multicellular eukaryotes.Bacteria have their own version of mitosis called “binary fission”.This is distinct from meiosis as bacteria typically have one circular chromosome,which is not contained within a nucleus, like eukaryotic chromosomes.
Only organisms which perform sexual reproduction. Archaeaand bacteria do not do this, so it might be tempting to think that unicellularorganisms do not sexually reproduce. However, there are exceptions; buddingyeast will form haploid spores under nutritional deprivation.
How long does this process take?
Mitosis is usually shorter than meiosis. The process can take over 10 hours for mammalian cells in culture [2], budding yeast can take ~80 minutes to complete a cell cycle [3], whilst bacteria can divide every 20 minutes.
Meiosis has various timescales in different organisms, which can be affected by several factors including temperature and environment of the organism, and the amount of nuclear DNA. The process lasts 6 hours in yeast but can last more than 40 years in human females, due to a developmental hold at prophase I, until ovulation. Other examples are 1-2 days in male fruit flies and ~ 24 days in human males. [1]
What is an example of a disease caused by an error in this process?
Uncontrolled mitosis occurs in cancer, where either genes that stop cell division (tumour suppressors) are switched off, or genes that encourage cell division (oncogenes) are overactive.
Errors in meiosis can lead to the wrong number of chromosomes ending up in germ cells, this is called aneuploidy. This can trigger miscarriage, but is occasionally tolerated. One example is Down’s syndrome, caused by trisomy 21. Another example is Klinefelter syndrome, where XY males have an additional X chromosome.
Etymology?
Mitosis is the Greek word for thread, after the thread-like chromosomes that can be seen under the microscope in dye-stained cells during cell division.
Meiosis means a “lessening” in Greek. This refers to the outcome of meiosis, where the genetic information in each new cell is halved.
First described by?
Walther Flemming in his 1882 work “Cell substance, nucleus and cell division.” [5]
Oskar Hertwig described the fusion of egg and sperm in the transparent sea urchin egg in 1876. [4]