B.7F-Evolutionary Mechanisms_B.10D Approaching – 03
Imagine a small population of white wildflowers. How can we explain the sudden appearance of red wildflowers? The red allele has moved into this population. There might be a nearby mixed population of the same wildflower. Insects carry pollen from flower to flower. The wind can randomly blow pollen between populations. Pollen contains genes.
Gene flow is the process that moves genes from one population to another. Genes can flow in both directions. Genes can be removed from a population. Some can be added to a population. Over time, the original white population will be a mixture of red and white flowers. Gene flow makes populations more similar.
What if a white variety of the flower did not exist? Suddenly a white flower appears in a population of all red. A change in the DNA of the flower color gene may have occurred. Mutation is a process that causes a permanent change in the DNA structure. The change must be able to be passed on to offspring.
Mutation introduces new versions of genes into the gene pool. Diversity is increased. A mutation is random. It does not appear because an organism needs it.
Sexual reproduction generates new combinations of genes in offspring. These combinations are not found in the parents. This process is known as genetic recombination.
There are three random events in recombination. Look at the diagrams of the three events. Genes cross over randomly during meiosis. Chromosomes sort independently when ovum and sperm form. Ovum and sperm unite by chance during fertilization. Genetic recombination increases the diversity of a population.
Genetic drift, gene flow, mutation, and genetic recombination are mechanisms of evolutionary change. They occur by random chance. They cause changes to the gene pool. They do not adapt a population to its environment. Their effect may be positive, negative, or neutral.