Chicken or egg, what came first? It’s a pretty simple question to answer. At first there was an egg. Out of this egg a chicken hatched. See, pretty simple right? If there was no egg there would be no chicken! But wait a second – where does that egg come from? A chicken must have laid the egg. No chicken, no egg.
Even back in the good old days people struggled to answer this question. Aristotles (384 – 322 BC) tried to figure out what was first and came to the conclusion that both must always have existed. More than 2000 years later we now know better. In today’s article we will finally solve this puzzle and make things clear. Or worse.
Mitosis
Mitosis is a stage in the cell cycle which produces two identical daughter cells from one mother cell. The mitosis runs in 6 stages:
Interphase: Is the phase between two mitoses and serves the preparation of the next mitosis. Is the longest phase which takes up to 90% of the cell division cycle. The interphase itself is not part of the mitosis, but is responsible for the DNA replication.
Prophase: The DNA in the nucleus has the form of a double helix. This double helix is wrapped around certain proteins. During the prophase the DNA is packed more densely and changes it appearance. The process is called DNA condensation. The chromosomes are now visible under a light microscope (See figure below). Mitotic spindles are built, which will later separate the chromosomes.
Metaphase: The spindles align the chromosomes in the equatorial plane. This is important to make sure that the next phase works correctly.
Anaphase: The two chromosomes are separated in the middle (kinetochores) and pulled towards the opposite sides of the cell.
Telophase: The separated chromosomes reached the opposite side of the cell and the daughter cells start to build their own membrane. The DNA condensation is reversed.
Cytokinesis: Two daughter cells with an own nucleus each are produced. The mitosis is finished.
Chicken Or Egg
Fig.1 Stages of cell replication.
A short note about the DNA packing. As told DNA is a double helix string which however has different appearance. During mitosis the condensation of DNA happens which puts the double helix into the form of chromosomes.
Chicken Or Egg
Fig.2 DNA condensation.
The meiosis is also a form of cell reproduction, but the daughter cells are not identical. Meiosis plays a great role in sexual reproduction where we need to mix the chromosomes to create a new and unique individual. If sexual reproduction by humans would follow only mitosis we all would look the same and there would be no different genders.
Chicken Or Egg
Fig.3 Stages of mitosis, meiosis and binary fission.
Once there was a chicken-like animal. This chickenlike-chicken laid some chicken-like eggs from which other chickenlike-chickens hatched. (Too many chicken-like chickens here) With every new generation mutations and changes in the DNA occur. Over a long period these mutations in the DNA caused that inside an egg a real chicken developed. And there we go, our first real chicken that hatched from an not chicken egg.
