Mitosis (Asexual Reproduction) Mitosis is the simple replication of cells. During mitosis, the original cell’s DNA is copied, so the two new cells have the same genetic code. Whenever you start with one cell, you’ll get two new ones that are the same. There are 5 basic steps in the cell life cycle: PMATI. Prophase→Metaphase→Anaphase→Telophase→Interphase Prophase is when the cell gets the idea that it's time to split. In half. During metaphase, the pieces line up to divide. Anaphase is when the split begins and half of the chromosomes go one way, while the other half go the other way. Telophase is when the divide is ending and the membrane closes, separating the cell. Interphase is like the resting state of the cell, after the divide is complete. Mitosis is used in asexual reproduction of organism and cells.
Meiosis (Sexual Reproduction) Unlike mitosis, the DNA is not duplicated during meiosis because there are two different cells with different DNA being combined. A cell is split and the two resulting cells are split again to get four cells. The 4 cells you get have 23 chromosomes each (instead of 46) and they combine with other cells, also with 23 chromosomes. This is important because a species needs to have a variety of genes in order to survive. Meiosis would create more genetic variabilitythan mitosis because the process creates more organisms than mitosis, so that automatically creates more options for a mutation or something different. Also, DNA is not duplicated during meiosis as it is during mitosis.
Genetic Variability and Crossover Genetic variability is how much organisms' genetic material differs from others around them, including physical appearance. There is a process that causes more genetic variability called crossover. During the process of crossover, two chromosomes exchange parts of their genetic material. This creates more variability because the genetic codes are ‘messed up’ even though genetic variability is not a bad thing. In fact, it is necessary for the survival of animals and humans. That’s because there needs to be backup. If one species starts to die out as a result of not being the fittest to survive, there needs to be another species to keep going.
Natural Selection Natural selection is a gradual process where certain genes and traits become more or less common based on the environment. It is an important part of evolution. For example, imagine a population of grey and brown squirrels. The brown squirrels blend into the environment better than the grey squirrels so they are less likely to be eaten. Over a long period of time, there are less and less grey squirrels and more brown squirrels because the brown fur is more useful and gets passed down more. Basically, who ever is fittest to survive will survive. Biological Reproduction and Sickle Cell Disease As you can see, environment affects biological reproduction. Reproduction will carry on for whichever species is more adapted to the environment-whichever species is fittest to survive. For example, the sickle cell disease is much more common in Africa than it is here in the United States. It's also better to be a carrier of the disease in Africa. That's not because of availability of facilities or treatment, but because of its usefulness to life there. In Africa, malaria is a serious disease that highly affects the population. Being a carrier of sickle cell prevents malaria, (click here to find out more) so that disease thrives more where it's most useful, which is Africa. In the United States, malaria is not a threat. Therefore, sickle cell has no useful purpose.