Question

Basic understanding of genetic heredity. DNA code must be understood but molecular details are not needed. Relation between genes, evolution, and natural selection. The distinction between learned behavioral adaptations and innate behavioral adaptations is important. In this context, what we have meant by “3 sources of knowledge in behavior” is crucial. Basics of behavior genetics and the notion of the heritability estimates. Gene-environment interactions are quite important as well.

Answer 1

The influence of genes on behavior has been well established in the scientific community. To a large extent, who we are and how we behave is a result of our genetic makeup. While genes do not determine behavior, they play a huge role in what we do and why we do it.

Behavioral genetics studies heritability of behavioral traits, and it overlaps with genetics, psychology, and ethology (the scientific study of human and animal behavior). Genetics plays a large role in when and how learning, growing, and development occurs. For example, although environment has an effect on the walking behavior of infants and toddlers, children are unable to walk at all before an age that is predetermined by their genome. However, while the genetic makeup of a child determines the age range for when he or she will begin walking, environmental influences determine how early or late within that range the event will actually occur.

Classical, or Mendelian, genetics examines how genes are passed from one generation to the next, as well as how the presence or absence of a gene can be determined via sexual reproduction. Gregor Mendel is known as the father of the field of genetics, and his work with plant hybridization (specifically pea plants) demonstrated that certain traits follow particular patterns. This is referred to as the law of Mendelian inheritance.

Genes can be manipulated by selective breeding, which can have an enormous impact on behavior. For example, some dogs are bred specifically to be obedient, like golden retrievers; others are bred to be protective, like German shepards. In another example, Seymour Benzer discovered he could breed certain fruit flies with others to create distinct behavioral characteristics and change their circadian rhythms.

The Influence of Behavior on Genes

Behavior can influence genetic expression in humans and animals by activating or deactivating genes.

Drugs and Alcohol

Prenatal exposure to certain substances, particularly drugs and alcohol, has detrimental effects on a growing fetus. The most serious consequences of prenatal drug or alcohol exposure involve newborn addiction and fetal alcohol syndrome (FAS). Fetal alcohol syndrome affects both physical and mental development, damaging neurons within the brain and often leading to cognitive impairment and below-average weight. Exposure to drugs and alcohol can also influence the genes of children and adults. Addiction is thought to have a genetic component, which may or may not be caused by a genetic mutation resulting from drug or alcohol use.

Temperature

Temperature exposure can affect gene expression. For example, in Himalayan rabbits, the genetic expressions of fur, skin, and eyes are regulated by temperature. In the warm areas of the rabbits’ bodies, the fur lacks pigment due to gene inactivity and turns white. On the extremities of the rabbits’ bodies (nose, ears and feet) the gene is activated and therefore pigmented (usually black).

Light

Light exposure also influences genetic expression. Thomas Hunt Morgan performed an experiment in which he exposed some caterpillars to light and kept others in darkness. Those exposed to certain light frequencies had corresponding wing colors when they became butterflies (for example, red produced vibrant wing color, whereas blue led to pale wings). Darkness resulted in the palest wing color, leading him to conclude that light exposure influenced the genes of the butterflies. In this manner a caterpillar’s behavior can directly affect gene expression; a caterpillar that actively seeks out light will appear different as a butterfly than one that avoids it.

Down syndrome is a human genetic defect in which there is an extra 21st chromosome. People with Down syndrome have distinctive physical features and often some type of developmental disability.

Phenylketonuria (PKU) is an inherited metabolic disorder. The presence of a particular gene keeps the individual from being able to process the amino acid phenylalanine. An excess of this chemical interferes with the formation of myelin in the brain and can produce a type of developmental disability. The genetic problem can be detected by a PKU test given at birth and can be regulated by dietary methods.