Question

What is evolution? What processes give rise to genetic variation? What processes can cause allele frequencies to change over time? (Section 12.6)

Short answer

Evolution is the change in species over time. Genetic variation arises from mutations, recombination, and gene flow. Allele frequencies change due to natural selection, genetic drift, and gene flow.

Step-by-step solution

- Define Evolution

Evolution is the process through which species of organisms undergo changes over time through genetic variation and natural selection. It encompasses the genetic changes in populations across generations.

- Processes Giving Rise to Genetic Variation

Genetic variation arises through several mechanisms including mutations, which are changes in the DNA sequence, recombination during sexual reproduction, and gene flow where new genes are introduced into a population from another population.

- Processes Causing Allele Frequency Changes

Allele frequencies within a population can change through natural selection, where traits that enhance survival and reproduction become more common, genetic drift, which is random changes in allele frequencies, and gene flow, the movement of alleles between populations. Additionally, mutations can introduce new alleles into a population.

Key concepts

Genetic Variation

Genetic variation is the foundation of evolution, providing the raw material on which natural selection acts. This diversity within a gene pool arises through various processes that increase the differences among individuals.
First, mutations play a crucial role. These are changes in the DNA sequence that can introduce new alleles (variants of a gene) into a population. Mutations happen randomly and can be caused by errors during DNA replication or by environmental factors such as radiation.
Second, recombination occurs during sexual reproduction. When parental DNA combines to form offspring, genes are shuffled, producing new genetic combinations. Recombination increases genetic diversity by mixing the alleles from both parents.
Lastly, gene flow introduces new genetic material into a population from another population. This movement of genes happens when individuals migrate between populations and breed with them, spreading their different alleles.
Genetic variation is vital because it allows populations to adapt to changing environments, enhancing their chances of survival and reproduction.

Natural Selection

Natural selection is a critical process in evolution where organisms better adapted to their environment tend to survive and reproduce more successfully. This gradually shifts the genetic makeup of the population.
Natural selection works on the principle that individuals with advantageous traits are more likely to survive and pass these traits to their offspring. Over time, these beneficial traits become more common in the population while disadvantaging or neutral traits may diminish.
Several factors influence natural selection:

• **Survival of the Fittest**: Individuals with traits that offer survival advantages in a specific environment are more likely to survive.
• **Reproductive Success**: Traits that improve reproductive success will likely be passed to the next generation.
• **Variability**: A variety of traits within a population allows natural selection to filter which traits are fit for survival and reproduction

This continuous process helps populations to adapt to their environments, providing resilience against changes such as new predators, diseases, or climate shifts.

Allele Frequencies

Allele frequencies represent how common a particular allele is within a population. Understanding what alters these frequencies is fundamental to grasping evolution.
Several processes can change allele frequencies over time:
1. **Natural Selection**: Traits that are beneficial for survival and reproduction increase in frequency, while less advantageous ones may decrease.
2. **Genetic Drift**: Random changes in allele frequencies can happen over generations, especially in small populations. This can lead to some alleles becoming more common purely by chance.
3. **Gene Flow**: The movement of alleles between populations through migration can alter allele frequencies. When individuals from one population breed with another, they introduce new alleles.
4. **Mutations**: As the original source of genetic variation, mutations can introduce new alleles. If these mutations are beneficial, they may increase in frequency through natural selection.
By monitoring these factors, scientists can understand how populations evolve and adapt over time.