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Explain how and why Genetic diversity increases through the processes of Crossing Over and Mutations.

Crossing Over -

Crossing over allows exchange of parts of chromosomes. This mixing and matching allows for new combinations of genes in a population. If this did not happen then “populations� of species would be less diverse. For example, a diploid organism, in this case a mouse, (having two copies of every chromosome) has a chromosome with the genes for eye color, and also the genes for fur color. If the mouse is heterozygous for eye color; the dominant R producing red eyes and the recessive giving brown eyes, and it is also heterozygous for fur color with a dominant F making white fur and the recessive f giving brown fur. One copy of the chromosome has the R and F alleles, and the other has the r and f alleles. If there is no crossing over, then R and F are always inherited together as are r and f. This means that any of the mouses’s offspring with white fur will always have red eyes. If there was crossing over then the offspring could have brown fur and red eyes.


What is a mutation?


The diversity of beetle species as seen in the picture is driven by genetic mutation. Mutations are changes in the genetic sequence, and they are a main cause of diversity among organisms. These changes occur at many different levels, and they can have widely differing consequences. There are two general types of mutations: point (gene) mutations and chromosomal mutations. Point mutations affect only one or a few nucleotides within a gene Chromosomal mutations change the number of chromosomes or the number or arrangement of genes in a chromosome (= change in chromosome structure) In biological systems that are capable of reproduction, we must first focus on whether they are inheritable; specifically, some mutations affect only the individual that carries them, while others affect all of the carrier organism's offspring, and further descendants. For mutations to affect an organism's descendants, they must: 1) occur in cells that produce the next generation, and 2) affect the hereditary material. Ultimately, the interplay between inherited mutations and environmental pressures generates diversity among species.


Genetics Standard 2