Evolution Test 9

Natural selection mainly leads to three selections. They are: Stabilizing selection, directional selection, and disruptive selection. Technical selection does not belong to natural selection. This classification is based on different organism-environmental relationship.

Stabilizing selection operates in a constant environment. It favors the average or complex phenotype and eliminates the extreme values. The mean value never changes. Also, the peak gets higher and narrower.

Mortality in babies is an example of stabilizing selection. It is all depended on the baby’s birth weight. The optimum birth weight is 7.3 pounds which favor this selection. Newborn infants with less than 5.5 pounds and more than 10 pounds have the highest mortality rate.

Directional selection is also known as progressive selection. This selection always operates in a changing environment. After this natural selection, mean value always changed.

In disruptive selection, the members of both extreme are selected. The average gets rejected. Most of the individuals get values other than the mean character value. The naturally selected members are shown by two peaks.

In disruptive selection, most of the individuals get the periphery values at both ends of the curve given in the graph. The population gets divided into two different groups. Hence, they have two peaks which resemble a two-humped camel.

Marine mollusca is also known as limpets. They are aquatic snails with a conical shaped shell with a muscular foot. They are members of the family Gastropoda. Their shell pattern shows disruptive selection.

Limpets shell has a continuous pattern with color ranging from pure white to dark tan. They either attached to white gooseneck barnacles or to tan colored rocks. The light-colored limpets camouflaged with white barnacles while tanned limpets camouflaged on tan-colored rocks. But, the limpets with intermediate shell patterns were conspicuous and were preyed by predatory shorebirds.

Allele frequencies does not vary from species to species. In a population, the frequency always remains fixed or constant according to Hardy Weinberg principle. The alleles and total genes in any population remain constant and hence stable.

According to Hardy Weinberg principle, the total sum of all the frequencies of the allele is one. It shows that the gene pool remains the same or constant, i.e. one. Hence, it can be also termed as genetic equilibrium.

Individual frequencies can be represented as p and q. But for a diploid organism, p and q explain the frequency of allele A and allele a. p² represents AA whereas q² represent aa.

Hardy Weinberg stated that there are six factors affecting this principle. They are Gene migration or gene flow, genetic drift, mutation, genetic recombination, and natural selection. Each factor plays a major role in evolution.

There are six factors affecting this principle. Among the factors, the genetic drop is not included in them. They only include Gene migration or gene flow, genetic drift, mutation, genetic recombination, and natural selection.

Gene migration or gene flow occurs when some species migrate from original to a new place. This changes the allele frequency in the old as well as a new place. So, new genes or alleles are being added to the new population and removed from the old one.

Gene flow occurs when gene migration occurs many or multiple times. When this occurs by a chance, a process called gene drift occurs. It cannot occur spontaneously, slowly or due to a disaster.