The genetic composition of an organism is what is referred to as the genotype. The genotype is composed of a pair of alleles and it is what is manifested as the phenotype or observable characteristics of an organism. The pairs of alleles are confined in a locus having different phenotypic dominance thereby causing dominant and recessive alleles. A population can be sad to be a breeding group where the genetic makeup of individuals is transmitted from a generation to the next. Therefore the genotype frequencies may change from a generation to the next due to factors such as mutation, selection, and genetic drift. The genotype frequency would only remain constant if the population is in the Hardy-Weinberg equilibrium. However, this is a very rare situation in life since it requires special conditions to be able to hold the genotype frequency constant. As the genotype frequency changes, it is possible to have the allele frequency remaining constant. Take for example two parents with blood groups AA and BB who end up producing offspring with blood group AB. The genotype frequency has changed from being homozygous to heterozygous; however, the allele frequency remains to be 1:1. It can therefore be concluded that it is possible for a genotype frequency to change s the allele frequency is constant.
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The bright red coloring of male stickleback fish is the phenotypic expression of their genes. On mating with the female stickleback fish, they produce offspring that either has the bright red coloring or a blend of the two colors. Since the bright red coloration makes them conspicuous, the predators become prone to being preyed on by the predators. In a situation where all the predators are removed from the environment, the population of the bright red coloring male stickleback fish increases. Once their population increases and the fact that they are preferred mates of the female stickleback fish there will be an increased number of offspring with bright red coloring. The reason behind this is that the bright red coloring is a result of a dominant gene that expresses itself in the offspring. However, this situation will not be arrived at immediately. It will be progressive with the first set of offspring having a partly bright red colored population then after subsequent generations of mating the whole population is highly composed of the bright red colored stickleback fish.
According to the context of natural selection which essentially entails a trait being prevalent or less in a population the above situation is based on the same. Natural selection could either be a result of survival or reproduction in the population. In the case of the stickleback fish, both mechanisms are applied to make the bright red-colored stickleback fish dominate the population. Survival mechanism is applied when the predators are all removed from the environment to make the bright red colored male stickleback fish safe hence increasing their numbers. At the same time, reproduction comes in since the bright red colored stickleback male fish is preferred by the female stickleback fish as their mates. Therefore an increase in their numbers would enhance reproduction hence increasing the population of the bright red colored stickleback fish in the environment.