Gene Pool
The term gene pool refers to the total sum of genetic information contained on the genes within in a population at any given time. A gene pool can be assigned to any set group or population. This is true for plants, animals, and humans alike. Each gene pool contains all of the inherited information for all of the traits of the members of the population.
Genetic information, in the form of deoxyribonucleic acid (DNA), is passed from generation to generation. It is the genetic information that determines, or has a potential to determine, characters and traits expressed with a population (e.g., eye color, hair color, etc)
Each gene is a segment of DNA, and sequencing of the four base molecules of DNA create the gene. Variations in the nucleotide sequence account for variations in genes. A form of a gene is termed an allele. Although individuals may carry different alleles, each particular gene is found on the same chromosome in each individual. The long, linear strings of DNA are arranged into smaller packages known as chromosomes. There are 46 chromosomes in normal human cells. The 46 chromosomes can be matched into 23 pairs. One of each pair is inherited from the mother's egg and one of each pair is inherited from the father's sperm. Human cells contain two copies of each chromosome and likewise two copies or alleles of each gene. Each individual receives one allele from each parent because they receive one of each of the 23 chromosomes from each parent.
Although each person has 46 chromosomes, the DNA that makes up those chromosomes is slightly different from individual to individual. It is this variation within specific genes that gives the diversity observed throughout populations around the world and creates the gene pool for the human species.
Different versions of the same gene are referred to as alleles. Blood types are examples of alleles. In humans, there are several different blood types, including A, B, O, and AB. These arise by various combinations of the three blood-type alleles; the A-allele, the B-allele, and the O-allele. The specific blood type a person has depends on the exact blood type alleles they inherited from their parents. For example, a person may inherit two O-alleles, in which case they would have type O blood, or they may inherit an A and a B-allele, in which case they would have type AB blood, and so on.
Population genetics is the study of genetic variation within a population. This includes the subtle changes in DNA sequences and the frequencies of these different forms. Changes within the DNA sequences may arise through several pathways. Mechanisms commonly studied by population geneticists include mutation, natural selection, and genetic drift.
Mutations are changes within the DNA sequence that alter the original directions encoded within DNA. Mutation may result from damage to DNA, or a mistake in the replication of DNA resulting in a change in sequence. The majority of mutations arise by chance although some may be caused by environmental factors, such as toxins that penetrate the cells of the body and attack the DNA. Natural selection is the difference in mortality (death rates) and fertility (birth rates) between different genetic types. The interplay of the expressed phenotype and the environment influences natural selection. If the phenotype is favorable, the individual survives and perpetuates his or her genetic profile in the gene pool. Genetic drift is a process by which the frequencies of specific alleles change, by chance, within a population.
Each gene pool accounts for all of the alleles for all of the traits of the members of a population. Within a population, different alleles will occur at different frequencies. For instance, approximately 44% of the population has type O blood, 42% of the population has type A blood, 10% of the population has type B blood, and four percent of the population has type AB blood. The percentages of each blood type are directly related to the frequency of each blood type allele. The more frequent the A-allele, the more frequent type A blood would be seen in the population.
There are several projects underway at this time in an effort to further understand the gene pool, population genetics, and the human genome. The Human Genome Diversity Project (HGDP) is an international project that seeks to understand the diversity and unity of the entire human species. The Human Genome Project, a separate venture from HGDP, made the news in 2000 when scientists announced they had elucidated a working draft of the human genome sequence.
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