Explanation:
-increases genetic variation
-increases the fitness of a species
Further Explanation:
All the genetic information within the eukaryotic cell is stored within the nucleus as helical DNA. This DNA is tightly wound around histones as chromosomes. To produce daughter cells during cell division, the chromosomes (total number of chromosomes (2n)) are copied before the cell splits into two daughter cells. This process is known as mitosis, and occurs in cell division and growth processes. Two new nuclei are formed, along with identical cells. These are the same as the parent cell and the chromosome number (2n) is maintained.
Conversely in meiosis, the number of chromosomes (2n) is halved through meiotic divisions, producing 4 (n) germ cells (sperm or eggs), each containing half the number of chromosomes as its parent cell. During the process of cell division, spontaneous changes within the genome can arise. These mutations are errors occur when copies of the DNA within the cell are made; mutations may range from small changes called single nucleotide polymorphisms, to large scale deletions, and additions which span multiple genes. There are two types:
- somatic: these only occur within certain cells, and arise from environmental factors such as UV light
- hereditary: occur within germ cells of the parent and later the fertilized egg which forms a zygote; these are present within all cells of the new organism.
Like other events, such as crossing over during mitosis and meiosis, mutations lead to increases in genetic variation. This variation refers to the genetic characteristics present within a species. Mutations are maintained within cells, as they form new traits called alleles, which may confer adaptations that increase the fitness of a species, along with ensuring survival by conferring a protective advantage
.
e.g. sickle cell anemia, a disease caused by a mutation, confers protection against the disease malaria.
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Two ways:
1. In prophase I of meiosis the homologous chromosomes synapse and crossing over occurs. This switches sections of two of the sister chromatids so the outer two chromatids have the same mix of alleles as the parents and the inner two chromatids have new combinations of alleles.
2. Meiosis puts only one of each kind of chromosome in the gametes, selecting one of each homologous pair at random. Then when each gamete joins with the gamete from the other parent, there are practically infinite combinations of the alleles possible.
