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Pigeons Pigeons get a new look – Jacobin pigeon Researchers have found that mutations in pigeon DNA can control a variety of traits, including the directions their feathers grow, like in this Jacobin pigeon. Charles Darwin raised pigeons and was interested in their breeding as an extreme example of domestic selection. Let's explore how variations and mechanisms of change occur in different populations.

Learning Objectives

After completing the topic, the student will be able to:

  • Explore how change in allele frequencies related to evolution of populations.
  • Define and distinguish the terms directional, disruptive and sexual selection.
  • List the five conditions necessary to maintain Hardy–Weinberg equilibrium.
  • Apply the Hardy – Weinberg principle to estimate equilibrium genotype frequencies.
  • List the agents of evolutionary change.
  • Classify the sources of variations within populations.
  • Define and discuss the term "mechanism of change" and explain how this phenomenon extends evolutionary species.
Mendel's experiments on pea plants Mendel's experiments on pea plants (Pisum sativum) over many generations

His observation on seven traits include
1.Color of flower is purple or white
2.Flower position is axil or terminal
3.Stem length is long or short
4.Seed shape is round or wrinkled
5.Seed color is yellow or green
6.Pod shape is inflated or constricted
7.Pod color is yellow or green
Modern Evolutionary Synthesis - Modern Synthetic Theory of Evolution

Evolution is the change over time of inherited traits found in a population of individuals. Inherited traits are distinguishing characteristics comprising a phenotype encompassing such observables as physiology, anatomy, biochemistry and behavior that are passed on from one generation to the next.

Charles Darwin’s work on "Origin of Species" led to overwhelming acceptance of theory of evolution by natural selection within the scientific community. In the 1930s, Darwinian natural selection was combined with Gregor Mendelian’s theory of genetics as the basis for biological inheritance and mathematical population genetics to form the modern evolutionary synthesis, in which the connection between the units of evolution (genes) and the mechanism of evolution (natural selection) was made.

This powerful explanatory and predictive theory has become the central organizing principle of modern biology, providing a unifying explanation for the diversity of life on Earth. In the 1940’s, the identification of DNA as the genetic material by Oswald Avery and colleagues and the subsequent publication of the structure of DNA by James Watson and Francis Crick in 1953, demonstrated the physical basis for inheritance. Since then, genetics and molecular biology have become core parts of evolutionary biology.

The modern theory of evolution is based on two primary key points: All living beings are related to each other to varying degrees through common decent, developed from a single common ancestor. The origin of a new species results from random heritable genetic mutations or changes, some of which are more likely to spread and persist in a gene pool rather than others.

Albinism Albinism - Congenital disorder Albinism is associated with a number of vision defects, such as Photophobia, Nystagmus (voluntary and involuntary eye movement) and Astigmatism (blurred vision). Lack of skin pigmentation makes for more susceptible to sunburn and skin cancers.
Heredity or Inheritance

Living organisms are distinguished by their ability to reproduce their own kind. Only apple trees produce apples, and only lions can make more lions. Biological inheritance or heredity is the process by which an offspring cell or organism acquires or becomes predisposed to characteristics of its parent cell or organism. The transmission of traits from one generation to the next is called heredity. Along with inherited similarity, there is also variation, Offspring differ somewhat in appearance from parents and siblings. Through inheritance, variations exhibited by individuals can accumulate and cause a species to evolve.

In humans, for example, eye color is an inherited characteristic, which individuals can inherit from one of their parents. Inherited traits are controlled by genes and the entire set of genes within an organism’s genome is called its genotype. The complete set of observable traits that make up the structure and behavior of an organism is called its phenotype. These traits come from the interaction of its genotype with the environment.

As a result, not every aspect of an organism’s phenotype is inherited. Suntanned skin results from the interaction between a person’s genotype and sunlight; thus, a suntan is not hereditary. However, people have different responses to sunlight, arising from differences in their genotype; a striking example is individuals with the inherited trait of albinism (Albinism is a congenital disorder characterized by the complete or partial absence of pigment (melanin) in the skin, hair and eyes due to defect of tyrosinase, a copper–containing enzyme involved in the production of melanin.), who do not tan and are highly sensitive to sunburn.