Genetic variability, mutations and sexual reproduction

Genetic variability, mutations and sexual reproduction

Genetic variability is the presence of generation of genetic difference

Juan Fernando Arias Siabato, Juan Diego Burgos Ruiz

It can be caused thanks to:

• “Homologous recombination: during meiosis in sexual organisms, two homologous chromosomes cross over another and exchange genetic material. The chromosomes the split apart and are ready to contribute to forming an offspring.
• Immigration, emigration, and translocation during meiosis in sexual organism, two homologous chromosomes cross over one another and exchange genetic material. The chromosomes allows for even more genetic variability in one’s offspring.
• Polyploidy having more than two homologous chromosomes allows for even more recombination during meiosis allowing for even more genetic variability in one’s offspring.
• Diffuse centromeres in asexual organisms where the offspring is an exact genetic copy of the parent, there are limited sources of genetic variability.
• Genetic mutations, which contribute to genetic variability whitin a population and can have positive, negative, or neutral effects on a fitness”. (Wikipedia 2017)

To explain the relation between these three concepts (genetic variability, mutations, sexual reproduction) first we have to explain each one specifically.

“The genetic variability can inform us about our origins and history. Humans are relatively homogeneous genetically, reflecting a recent common origin. Anatomically modern humans probably originated in Africa, undergoing population bottleneck as some left to colonize the rest of the world. Because these events are fair recent, and because of extensive gene flow within major human population, most genetic variation can be found    within major human population. Genetic data also provide useful information about the origins and histories of individual human populations. As our capacity to collect and analyze data on human on human genetic variation increases our understanding of human evolutionary history will continue to grow”. (Jorde, 2003)

“The mutations a gene mutation is a permanent alteration in DNA sequence that makes up a gene, such that the sequence differs from what is found in most people. Mutations range in size; they can affect anywhere from a single DNA building block (base pair) to a large segment of a chromosome that includes multiple genes.

Gene mutations can be classified in two major ways:

• Hereditary mutations are inherited from parent and are presented throughout a person’s life in virtually every cell in the body. These mutations are also called germline mutations because they are presents in the parents egg or sperm cells, which are also called germ cells, when an egg and a sperm cell unite, the resulting fertilized egg cell receives DNA from both parents, if this DNA has a mutation, the child that grows from the fertilized egg will have the mutation in each of his or her cells.

• Acquired (or somatic) mutations occurs at some time during a person’s life and are present only in certain cells, not in every cells, not in every cell in the body. These changes can be caused by environmental factors such as ultraviolet radiation from the sun, or can occur in an error is made as DNA copies itself during cell division. Acquired mutations in somatic cells (cells other than sperm and egg cells) cannot br passed to the next generation.

Somatic mutations that happen in a single cell early in embryonic development can lead to a situation called mosaicism. These genetic changes are not present in a parent’s egg or sperm cell, or in the fertilized egg, but happen abit later when the embryo includes several cells. As all the cells divided during growth and development, cells that arise from the cell with the altered gene will have the mutation, while other cells will not. Depending on the mutation and how many cells are affected, mosaicism may or may not cause health problems”. (Reference, 2018)

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