This document discusses factors that influence natural selection: 1. Genetic variety within species, brought about by mutations and genetic recombination, allows for variation on which natural selection can act. 2. Gene expression influences how genes determine traits. 3. Excess reproduction, the ability of most species to produce more offspring than can survive, means individuals must compete for limited resources. Together, genetic variety, gene expression, and excess reproduction exert influence on the process of natural selection.

1. WHAT INFLUENCES NATURAL SELECTION EVOLUTION

2. REVIEW OF NATURAL SELECTION PRINCIPLES Principles of Natural Selection A. Observations about populations: 1. Natural populations have an inherent reproductive capacity to increase. 2. As a population expands, resources that are used by its individuals (such as food and living space) eventually become limited. 3. When resources are limited, individuals of a population compete for them.

3. PRINCIPLES OF NATURAL SELECTION B. Observation about genetics 1. Individuals of a species share certain traits. 2. Individuals of a natural population vary in the details of their shared traits. 3. Traits have a heritable basis, in genes. Alleles (slightly different forms a gene) arise by mutation.

4. PRINCIPLES OF NATURAL SELECTION C. Inferences 1. A certain form of a shared trait may make its bearer more competitive at securing a limited resource. 2. Individuals better able to secure a limited resource tend to have more offspring than others of a population. 3. Thus, an allele associated with an adaptive trait tends to become more common in a population over time.

5. What Influences Natural Selection? There are factors that influence natural selection? 1. Genetic variety > Within a species (the fact that not all organisms of a given kind contain the same genes) is brought about by mutations (changes to genes) and genetic recombination (the mixing of gene combinations that occurs during sexual reproduction). 2. Gene expression The degree to which genes determine a trait. 3. Excess reproduction > the ability of most species to reproduce excess offspring.

6. What Influences Natural Selection? So genetic variety, gene expression and excess reproduction all exert influence on the process of natural selection.

7. 1. GENETIC VARIETY If all individuals were identical genetically, it would not matter which ones reproduce – the same genes would be passed to the next generation and natural selection would not occur. Under genetic variety are two processes that make genes vary in an organism. 1. Mutation 2. Genetic Recombination

8. GENETIC VARIETY 1. Mutation – it is a change in either the amount or the arrangement of the genetic material in a cell. It can happen to any type of cell. If it occurs in a gamete, the resulting characteristic could be inherited. Mutations occur in the normal body cells as well. If mutations occur on these normal body cells (not on gametes), these are called somatic mutations and they cannot be passed on to the next generation.

9. GENETIC VARIETY – 1. Mutation Chromosome mutations involve large scale changes and may involve parts, or even, whole chromosomes. Point mutation (Gene mutation) on the other hand are on a much smaller scale. It involves a change to relatively small number of bases in the genetic material.

10. GENETIC VARIETY – 1. Mutation The rate at which mutation takes place can be increased by exposure to various mutagens. 1. Ultraviolet radiation 2. X-rays 3. Organic chemicals

11. GENETIC VARIETY – 1. Mutation Genes of a particular trait originated as a result of mutations sometime in the past and have been maintained with in the species as result of sexual reproduction. Many mutations are unfavorable since they originate from a random change in a gene or genetic combination that has already proven valuable to the organism. (These mutation is called lethal mutation).

12. GENETIC VARIETY – 1. Mutation But it is quite possible that a new beneficial gene could come about as a result of random mutation from over thousands of generations from populations of millions of individuals, each of whom has thousand of genes. We can consider this type of mutation a beneficial mutation or neutral mutation.

13. GENETIC VARIETY – 1. Mutation Every gene originated from an existing gene. As an example we could say: 1. That the blue eye gene is a mutation of the brown eye gene. 2. That the blond hair gene is a mutation of the brown hair gene.

14. Evolution Presentation