Vocabulary: mutations, natural selection, variations
Variations are differences between groups of organisms of one species. Mutation is one source of variation between different groups within a species. The variation of organisms within a species increases the likelihood that at least some members of the species will survive under changed environmental conditions.
Sources of Variation
- The exchanging and recombining of genes during meiosis and fertilization result in a great variety of new possible gene combinations from that of the parents.
- Mutations are random changes in the genes or DNA of sex cells may result in new gene combinations creating variation in the offspring formed from these.
Only mutations that occur in sex cells can be passed on to the offspring. Mutations which occur in other cells can be passed on to other body cells only. The experiences an organism has during its lifetime can affect its offspring only if the genes in its own sex cells are changed by the experience.
Variation and Evolution
Evolution is the consequence of the following factors:
- the potential for a species to increase its numbers
- the genetic variability of offspring due to mutation and recombination of genes
- a finite supply of the resources required for life
- the ensuing selection by the environment of those offspring better able to survive and leave offspring.
Some characteristics give individuals an advantage over others in surviving and reproducing, and the advantaged offspring, in turn, are more likely than others to survive and reproduce. The proportion of individuals that have advantageous characteristics will increase.
An Example of Variation Driving Natural Selection
Natural selection favors longer necks for a better chance to get higher leaves. Favored characteristic is passed on to next generation.
Original group exhibits variation in neck length. After many generations, the group is still variable, but shows a general increase in neck length.
The variation of organisms within a species increases the likelihood that at least some members of the species will survive under changed environmental conditions.
The great diversity of organisms is the result of billions of years of selection for favorable variations that has filled available niches of our planet with life forms.
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