Population Genetics Overview

Populations

• A species is a group of individuals with a common ancestry, able to breed and produce fertile offspring
• A population is a group of the same species in the same area, at the same time, which can interbreed
• A gene pool is all the alleles of all the genes in a population
• Allele frequency is the proportion of individuals with a single copy of an allele
• Allele frequencies change due to natural selection within and between populations

Population Genetics

• Populations can be seen as gene pools consisting of all alleles of all genes
• Populations evolve as allele frequencies change across generations
• Allele frequencies can be determined using the Hardy-Weinberg equation

Variation

• Within populations, there's phenotypic variation
• Continuous variation is polygenic (influenced by many genes), while discontinuous variation is monogenic (influenced by a single gene)
• Genetic variation comes from mutations, meiosis, and random fertilisation
• The environment affects how genes are expressed

The Effect of Selection on Allele Frequencies

• Predation, disease, and competition lead to differential survival and reproduction
• Individuals with advantageous traits are more likely to reproduce, passing on their favorable alleles
• This causes allele frequency changes within a population, leading to evolution
• Directional selection favors one extreme trait
• Stabilizing selection favors the average trait
• Disruptive selection favors both extreme traits, potentially leading to speciation.

Speciation

• Speciation is the formation of new species from existing ones
• Reproductive isolation, followed by genetic changes, results in the formation of new species
• Genetic differences between populations can arise from geographic isolation (allopatric speciation) or reproductive isolation within the same geographic area (sympatric speciation)
• Reproductive isolation can occur due to different breeding seasons, courtship behaviors, anatomical differences or genetic incompatibility
• Hybrid sterility occurs if the resulting offspring cannot produce viable gametes

Genetic Drift

• Genetic drift occurs when allele frequencies change due to chance events in a population (not selection pressures)
• It's more prominent in smaller populations, allowing chance fluctuations to greatly affect the gene pool
• Random gamete production and fertilization can lead to allele fluctuations

Ecosystems and Population Size

• A community consists of all the populations of various species interacting in a given area
• An ecosystem encompasses all living (biotic) and non-living (abiotic) factors within a defined area
• Every organism occupies a specific ecological niche, fitting its needs with abiotic and biotic factors
• Carrying capacity is the greatest population an area can sustain
• Limiting factors (abiotic and biotic) affect population size
• Population size can be estimated using methods like quadrats and mark-recapture

Succession

• Succession involves gradual changes in an ecosystem over time
• Primary succession starts on bare rock, with pioneer species gradually building soil, followed by other species
• Secondary succession occurs after a disturbance in an existing habitat
• Climax community is reached when a stable ecosystem is formed with a higher biodiversity

Conservation

• Conservation is maintaining biodiversity, including diversity between and within species
• Conservation efforts manage communities and ecosystems to preserve biodiversity from extinction risks
• The increasing human population and demand for resources create tension between human needs and conservation efforts

Explore the fundamental concepts of population genetics, including the definitions of species, populations, and gene pools. Understand how allele frequencies vary, the effects of natural selection, and the significance of genetic variation within populations. This quiz will enhance your knowledge of the mechanisms behind evolution and inheritance.