Sources of Phenotypic Variation
Sources of
Phenotypic
Variation
The creative force of evolution is natural selection acting on biological variation. Without variability among individuals, there could be no continued adaptation to a changing environment and no evolution (Organic Evolution).
There are actually several sources of variability, some of which we have already described. The independent assortment of chromosomes during meiosis is a random process that creates new chromosomal recombinations in the gametes. In addition, chromosomal crossing over during meiosis allows recombination of linked genes between homologous chromosomes, further increasing variability. The random fusion of gametes from both parents produces still another source of variation.
There is a story that George Bernard Shaw once received a letter from a famous actress who suggested that they conceive a perfect child who would combine her beauty and his brains. He declined the offer, pointing out that the child could just as well inherit her brains and his beauty. Shaw was correct; the fusion of parental gametes is random and thus unpredictable.
Thus sexual reproduction multiplies variation and provides the diversity and plasticity necessary for a species to survive environmental change. Sexual reproduction with its sequence of gene segregation and recombination, generation after generation, is, as the geneticist T. Dobzhansky has said, the “master adaptation which makes all other evolutionary adaptations more readily accessible.”
Although sexual reproduction reshuffles and amplifies whatever genetic diversity exists in the population, there must be ways to generate new genetic variation. This happens through gene mutations and, sometimes, through chromosomal aberrations.
The creative force of evolution is natural selection acting on biological variation. Without variability among individuals, there could be no continued adaptation to a changing environment and no evolution (Organic Evolution).
There are actually several sources of variability, some of which we have already described. The independent assortment of chromosomes during meiosis is a random process that creates new chromosomal recombinations in the gametes. In addition, chromosomal crossing over during meiosis allows recombination of linked genes between homologous chromosomes, further increasing variability. The random fusion of gametes from both parents produces still another source of variation.
There is a story that George Bernard Shaw once received a letter from a famous actress who suggested that they conceive a perfect child who would combine her beauty and his brains. He declined the offer, pointing out that the child could just as well inherit her brains and his beauty. Shaw was correct; the fusion of parental gametes is random and thus unpredictable.
Thus sexual reproduction multiplies variation and provides the diversity and plasticity necessary for a species to survive environmental change. Sexual reproduction with its sequence of gene segregation and recombination, generation after generation, is, as the geneticist T. Dobzhansky has said, the “master adaptation which makes all other evolutionary adaptations more readily accessible.”
Although sexual reproduction reshuffles and amplifies whatever genetic diversity exists in the population, there must be ways to generate new genetic variation. This happens through gene mutations and, sometimes, through chromosomal aberrations.
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