Chapter 2: Biology and Psychology

Chapter 2: Biology and Psychology

Learning Outcomes Describe the nervous system, including neurons, neural impulses, and neurotransmitters. List the structures of the brain and their functions.

Learning Outcomes Explain the role of the endocrine system and list the endocrine glands. Describe evolutionary psychology and the connections between heredity, behavior, and mental processes.

The Nervous System: On Being Wired
LO1 Describe the nervous system, including neurons, neural impulses, and neurotransmitters

Neurons Neurons Glial cells Specialized cells of the nervous system
Receive and pass messages Glial cells Remove waste products Nourish and insulate neurons Direct growth of neurons neurons – a specialized cell of the nervous system that receives and transmits messages glial cells – cells that remove dead neurons and waste products from the nervous system, nourish and insulate neurons, form myelin, and play a role in neural transmission of messages

Neurons Vary according to location and function
Neurons include cell body, axon, and dendrites As brain matures axon lengthens and dendrites proliferate Myelin dendrites – rootlike structures, attached to the cell body of a neuron, that receive impulses from other neurons axon – a long, thin part of a neuron that transmits impulses to other neurons from branching structures called axon terminals or terminal buttons myelin – a fatty substance that encases and insulates axons, facilitating transmission of neural impulses

The Anatomy of a Neuron Figure 2.1: The Anatomy of a Neuron - “Messages” enter neurons through dendrites, are transmitted along the trunk-like axon, and then are sent from axon terminal buttons to muscles, glands, and other neurons. Axon terminal buttons contain sacs of chemicals called neurotransmitters. Neurotransmitters are released into the synaptic cleft, where many of them bind to receptor sites on the dendrites of the receiving neuron. Go to 4ltrpress.cengage.com/psych to access an interactive version of this figure.

Truth or Fiction? A single cell can stretch all the way from your spine to your toe. Truth or Fiction? A single cell can stretch all the way from your spine to your toe. TRUE A single cell can stretch all the way from your spine to your toe.

Truth or Fiction? A single cell can stretch all the way from your spine to your toe. TRUE! Truth or Fiction? A single cell can stretch all the way from your spine to your toe. TRUE A single cell can stretch all the way from your spine to your toe.

Neurons Afferent Neurons Efferent Neurons
Transmit messages from sensory receptors to the spinal cord and brain Efferent Neurons Transmit messages from bran or spinal cord to muscles and glands afferent neurons - neurons that transmit messages from sensory receptors to the spinal cord and brain. Also called sensory neurons efferent neurons – neurons that transmit messages from the brain or spinal cord to muscles and glands. Also called motor neurons

Neural Impulse Electrochemical messages travel within neurons
Resting potential Neuron is not responding to other neurons Action potential Conduction of neural impulse along axon neural impulse – the electrochemical discharge of a nerve cell, or neuron polarize – to ready a neuron for firing by creating an internal negative charge in relation to the body fluid outside the cell membranes resting potential – the electrical potential across the neural membrane when it is not responding to other neurons depolarize – to reduce the resting potential of a cell membrane from about 70 millivolts toward zero action potential – the electrical impulse that provides the basis for the conduction of a neural impulse along an axon of a neuron

Truth or Fiction? Messages travel in the brain by means of electricity. Truth or Fiction? Messages travel in the brain by means of electricity. TRUE The messages are within neurons. Communication between neurons, however, is carried out quite differently.

Truth or Fiction? Messages travel in the brain by means of electricity. TRUE! Truth or Fiction? Messages travel in the brain by means of electricity. TRUE The messages are within neurons. Communication between neurons, however, is carried out quite differently.

Firing: Neuron to Neuron
Conduction of neural impulse along the length of a neuron Threshold Incoming messages reach a strength at which neuron will fire

Truth or Fiction? A brain cell can send out hundreds of messages each second – and manage to catch some rest in between. Truth or Fiction? A brain cell can send out hundreds of messages each second – and manage to catch some rest in between. TRUE During the refractory period, the neuron is insensitive to messages from other neurons and will not fire.

Truth or Fiction? A brain cell can send out hundreds of messages each second – and manage to catch some rest in between. TRUE! Truth or Fiction? A brain cell can send out hundreds of messages each second – and manage to catch some rest in between. TRUE During the refractory period, the neuron is insensitive to messages from other neurons and will not fire.

All-or-none principle Every time a neuron fires, it transmits an impulse of the same strength. Refractory period Period of recovery time between firings all-or-none principle – the fact that a neuron fires an impulse of the same strength whenever its action potential is triggered refractory period – a phase following firing during which a neuron is less sensitive to messages from other neurons and will not fire

Synapse Fluid-filled gap (Synaptic cleft) between Axon terminal from transmitting neuron, and Dendrite of receiving neuron synapse – a junction between the axon terminals of one neuron and the dendrites or cell body of another neuron

Neurotransmitters Neurotransmitters Synaptic vesicles
Chemical substances that communicate from one neuron to another Synaptic vesicles Contain neurotransmitters in the axon terminals neurotransmitters – chemical substances involved in the transmission of neural impulses from one neuron to another

Neurotransmitters Receptor site Reuptake
On dendrite of receiving neuron Reuptake Neurotransmitters reabsorbed receptor site – a location on a dendrite of a receiving neuron tailored to receive a neurotransmitter

Neurotransmitters Excitatory neurons Inhibitory neurons
Cause other neurons to fire Inhibitory neurons Prevent other neurons from firing

Neurotransmitters of Interest to Psychologists
Acetylcholine (ACh) Controls muscle contractions Paralysis Prevalent in hippocampus Memory Alzheimer’s disease acetylcholine (Ach) – a neurotransmitter that controls muscle contractions hippocampus – a part of the limbic system of the brain that is involved in memory formation

Dopamine Pleasure, voluntary movement, learning, memory Parkinson’s disease Schizophrenia dopamine – a neurotransmitter that affects the ability to perceive pleasure, voluntary movement, and learning and memory; it is involved in Parkinson’s disease and that appears to play a role in schizophrenia Photo: The boxer Muhammad Ali and actor Michael J. Fox are two of the better-known individuals who are afflicted with Parkinson’s disease.

Norepinephrine Excitatory neurotransmitter Accelerates heart rate, affects eating, linked to activity levels, learning and remembering Mood disorders, depression, bipolar disorder norepinephrine – a neurotransmitter whose action is similar to that of the hormone epinephrine and that may play a role in depression

Serotonin Emotional arousal and sleep Eating disorders, alcoholism, depression, aggression, insomnia serotonin – a neurotransmitter involved in emotional arousal and sleep; deficiencies of serotonin have been linked to eating disorders, alcoholism, depression, aggression, and insomnia

Gamma-aminobutyric acid (GABA) Inhibitory may help relax anxiety reactions Depression gamma-amniobutyric acid (GABA) - an inhibitory neurotransmitter that apparently helps calm anxiety

Endorphins Occur naturally within the brain and bloodstream Inhibit pain May be connected to indifference to pain Runner’s high endorphins – inhibitory neurotransmitters that occur naturally in the brain and in the bloodstream and are similar to the narcotic morphine in their functions and effects

Parts of the Nervous System
Central Nervous System Brain and spinal cord Peripheral Nervous System Sensory (afferent) and motor (efferent) neurons nerve – a bundle of axons from many neurons central nervous system – the brain and spinal cord peripheral nervous system – the part of the nervous system consisting of the somatic nervous system and the autonomic nervous system

The Divisions of the Nervous System
Figure 2.4: The Divisions of the Nervous System - The nervous system contains two main divisions: the central nervous system and the peripheral nervous system. The central nervous system consists of the brain and spinal cord. The peripheral nervous system contains the somatic and autonomic systems. In turn, the autonomic nervous system has sympathetic and parasympathetic divisions. Go to 4ltpress.cengage.com/pysch to access an interactive version of this figure.

Peripheral Nervous System
Somatic Nervous System Sensory and motor neurons Transmits messages to the brain and purposeful body movements from the brain Autonomic Nervous System Regulates glands and muscles of internal organs Contains sympathetic and parasympathetic divisions somatic nervous system – the division of the peripheral nervous system that connects the central nervous system with sensory receptors, skeletal muscles, and the surface of the body autonomic nervous system (ANS) – the division of the peripheral nervous system that regulates glands and activities such as heartbeat, respiration, digestion, and dilation of the pupils

Truth or Fiction? Fear can give you indigestion.
Truth or Fiction? Fear can give you indigestion. TRUE The parasympathetic division stimulates digestive processes, but the sympathetic branch, which can be activated by fear, inhibits digestion. Thus fear can give you indigestion.

Truth or Fiction? Fear can give you indigestion. TRUE!
Truth or Fiction? Fear can give you indigestion. TRUE The parasympathetic division stimulates digestive processes, but the sympathetic branch, which can be activated by fear, inhibits digestion. Thus fear can give you indigestion.

Branches of Autonomic Nervous System
Sympathetic Most active during emotional responses Spend the body’s reserves of energy Parasympathetic Most active during processes that restore body’s reserve of energy sympathetic division – the branch of the ANS that is most active during emotional responses, such as fear and anxiety, that spend the body’s reserves of energy parasympathetic division – the branch of the ANS that is most active during processes (such as digestion) that restore the body’s reserves of energy

The Branches of the Autonomic Nervous System
Figure 2.5: The Branches of the Autonomic Nervous System (ANS) - The parasympathetic branch of the ANS generally acts to replenish stores of energy in the body. The sympathetic branch is most active during activities that expend energy. The two branches of the ANS frequently have antagonistic effects on the organs they service.

Central Nervous System
Spinal Cord Transmits messages from sensory receptors to the brain and from the brain to muscle and glands Spinal Reflex Simple, unlearned response to stimulus Interneurons spinal cord – a column of nerves within the spine that transmits messages from sensory receptors to the brain to muscles and glands throughout the body spinal reflex – a simple, unlearned response to a stimulus that may involve only two neurons

Central Nervous System
Gray matter – nonmyelinated neurons White matter – myelinated neurons gray matter – the grayish neurons and neural segments that are involved in spinal reflexes white matter – axon bundles that carry messages from and to the brain

The Reflex Arc Figure 2.6: The Reflex Arc - Reflexes are inborn, stereotyped behavior patterns that have apparently evolved because they help individuals adapt to the environment even before they can understand and purposefully manipulate the environment. Here we see a cross section of the spinal cord, highlighting a sensory neuron and a motor neuron, which are involved in the knee-jerk reflex. In some reflexes, interneurons link sensory and motor neurons.

The Brain: Wider Than the Sky
LO2 List the structures of the brain and their functions.

Truth or Fiction? The human brain is larger than that of any other animal. Truth or Fiction? The human brain is larger than that of any other animal. FICTION A human brain weighs about 3 pounds, but the brains of elephants and whales may be four times as heavy. However, our brains account for a greater part of our body weight than do those of elephants or whales.

Truth or Fiction? The human brain is larger than that of any other animal. FICTION! Truth or Fiction? The human brain is larger than that of any other animal. FICTION A human brain weighs about 3 pounds, but the brains of elephants and whales may be four times as heavy. However, our brains account for a greater part of our body weight than do those of elephants or whales.

How Do Researchers Learn About the Functions of the Brain
Experimenting with the brain Assessing damage from trauma and disease Intentionally damaging parts of a brain Electrical probes to stimulate parts of the brain Electroencephalograph Measurement of electrical activity – brain waves electroencephalograph (EEG) – a method of detecting brain waves by means of measuring the current between electrodes placed on the scalp

The Electroencephalograph (EEG)
Figure 2.7: The Electroencephalograph (EEG) – The EEG detects brain waves that pass between electrodes that are attached to the scalp. It has been used to reveal electrical activity associated with relaxation and the stages of sleep.

How Do Researchers Learn About the Functions of the Brain (continued)
Brain-Imaging Techniques Computerized axial tomography (CAT or CT scan) Positron emission tomography (PET scan) Magnetic Resonance Imaging (MRI) Functional Magnetic Resonance Imaging (fMRI) computerized axial tomography (CAT or CT scan) – a method of brain imaging that passes a narrow X-ray beam through the head and measures the structures that reflect the beams from various angles, enabling a computer to generate a three-dimensional image positron emission tomography (PET scan) – a method of brain imaging that injects a radioactive tracer into the bloodstream and assesses activity of parts of the brain according to the amount of glucose they metabolize magnetic resonance imaging (MRI) – a method of brain imaging that places a person in a magnetic field and uses radio waves to cause the brain to emit signals that reveal shifts in the flow of blood, which, in turn, indicate brain activity functional MRI (fMRI) – a form of MRI that enables researchers to observe the brain “while it works” by taking repeated scans

The Parts of the Brain Figure 2.9: The Parts of the Brain - This view of the brain, split top to bottom, shows some of the most important structures. Note how close the hypothalamus is to the pituitary gland. The proximity allows the hypothalamus to readily influence the pituitary gland. The “valleys” in the cerebrum are called fissures.

Structures and Functions of the Brain
Hindbrain Medulla Pons Cerebellum “Little brain” medulla – an oblong area of the hindbrain involved in regulation of heartbeat, blood pressure, movement, and respiration pons – a structure of the hindbrain involved in respiration, attention, and sleep and arousal cerebellum – a part of the hindbrain involved in muscle coordination and balance

Reticular formation From hindbrain, ascends through midbrain into lower part of forebrain Vital to attention, sleep, arousal reticular formation – a part of the brain involved in attention, sleep, and arousal

Forebrain Thalamus Relay station for sensory stimulation Hypothalamus Regulates body temperature, motivation and emotion Hunger, thirst, sexual behavior, caring for offspring, aggression thalamus – an area near the center of the brain involved in the relay of sensory information to the cortex and in the functions of sleep and attention hypothalamus – a bundle of nuclei below the thalamus involved in body temperature, motivation, and emotion

Forebrain Limbic System Amygdala, hippocampus and parts of hypothalamus Involved in memory and emotion limbic system – a group of structures involved in memory, motivation, and emotion that forms a fringe along the inner edge of the cerebrum amygdala – a part of the limbic system that apparently facilitates stereotypical aggressive responses

The Limbic System Figure 2.10: The Limbic System - The limbic system is made up of structures that include the amygdala, the hippocampus, and parts of the hypothalamus. It is evolved fully only in mammals and forms a fringe along the inner edge of the cerebrum. The limbic system is involved in memory and emotion, and in the drives of hunger, sex, and aggression.

Cerebrum Responsible for thinking and language Cerebral Cortex Surface of cerebrum Corpus Callosum Connects two hemispheres cerebrum – the large mass of the forebrain, which consists of two hemispheres cerebral cortex - the wrinkled surface area (gray matter) of the cerebrum corpus callosum – a thick fiber bundle that connects the hemispheres of the cortex

The Cerebral Cortex Outer layer of cerebrum Two Hemispheres Four Lobes
Frontal, Parietal, Temporal and Occipital

The Lobes of the Cerebral Cortex
Occipital Lobe Vision Temporal Lobe Hearing and Auditory functions Parietal Lobe Somatosensory Cortex Frontal Lobe Motor Cortex somatosensory cortex – the section of cortex in which sensory stimulation is projected. It lies just behind the central fissure in the parietal lobe. motor cortex – the section of cortex that lies in the frontal lobe, just across the central fissure from the sensory cortex; neural impulses in the motor cortex are linked to muscular responses throughout the body.

Truth or Fiction? If a surgeon were to stimulate a certain part of your brain electrically, you might swear that someone had stroked your leg. Truth or Fiction? If a surgeon were to stimulate a certain part of your brain electrically, you might swear that someone had stroked your leg. TRUE The action would be sensed in the somatosensory cortex.

Truth or Fiction? If a surgeon were to stimulate a certain part of your brain electrically, you might swear that someone had stroked your leg. TRUE! Truth or Fiction? If a surgeon were to stimulate a certain part of your brain electrically, you might swear that someone had stroked your leg. TRUE The action would be sensed in the somatosensory cortex.

The Geography of the Cerebral Cortex
Figure 2.11: The Geography of the Cerebral Cortex - The cortex has four lobes: frontal, parietal, temporal, and occipital. The visual area of the cortex is in the occipital lobe. The hearing or auditory cortex lies in the temporal lobe. The motor and somatosensory areas—shown above—face each other across the central fissure. Note that the face and the hands are “super-sized” in the motor and somatosensory areas.

Thinking, Language, and the Cortex
Association areas Not primarily involved in sensation or motor activity Responsible for learning, thought, memory and language Association areas in frontal lobe Responsible for executive functions Executive functions such as problem solving, making plans, and decision making.

Language Functions Two hemispheres of the brain mirror and differ
Left hemisphere contains language functions for nearly all people If damaged before age 13, speech functions would transfer to right hemisphere Two key language areas Broca’s area and Wernicke’s area Damage in either causes aphasia aphasia – a disruption in the ability to understand or produce language

Broca’s and Wernicke’s Areas
Figure 2.12: Broca’s and Wernicke’s Areas of the Cerebral Cortex – The areas that are most involved in speech are Broca’s area and Wernicke’s area. Damage to either area can produce an aphasia – a disruption of the ability to understand or produce language.

Language Functions Wernicke’s Area Angular Gyrus Temporal Lobe
Wernicke’s aphasia Impairs ability to comprehend speech and think of words to express own thoughts Angular Gyrus Translates visual into auditory information Damage impairs reading ability Wernicke’s aphasia – a language disorder characterized by difficulty comprehending the meaning of spoken language

Language Functions Broca’s Area Frontal Lobe Production of speech
Broca’s aphasia Understand language but speak slowly and laboriously Broca’s aphasia – a language disorder characterized by slow, laborious speech

Left Brain, Right Brain Left-brained Right-brained
Logical and intellectual Right-brained Intuitive, creative and emotional Hemispheres do not act independently Functions overlap and they respond simultaneously

Handedness Left-handed Origins of handedness
Somewhat greater-than-average probability of language problems and certain health problems More likely than right-handed people in gifted artists, musicians, and mathematicians Origins of handedness Genetics

Split-Brain Experiments
Severe cases of epilepsy may require split-brain operations Examples of “two brain” phenomenon Caused by inability of one hemisphere to communicate with the other epilepsy – temporary disturbances of brain functions that involve sudden neural discharges

A Divided Brain Experiment
[Insert Figure 2.13] Figure 2.13: A Divided Brain Experiment – In the drawing on the left, we see that visual sensations in the left visual field are projected in the occipital cortex of the right hemisphere. Visual sensations from the right visual field are projected in the occipital cortex in the left hemisphere. In the divided-brain experiment diagrammed on the right, a person with a severed corpus collosum handles a key with his left hand and perceives the written word key in this left visual field. The word “key” is projected in the right hemisphere. Speech, however, is usually a function of the left hemisphere. The written word “ring,” perceived by the right visual field, is projected in the left hemisphere. So, when asked what he is handling, the divided-brain subject reports “ring,” not “key.”

The Endocrine System LO3 Explain the role of the endocrine system and list the endocrine glands.

Endocrine System Comprised of ductless glands that release hormones into the bloodstream Hormones Regulate growth, metabolism and some behaviors Maintain steady bodily states gland – an organ that secretes one or more chemical substances such as hormones, saliva, or milk endocrine system – the body’s system of ductless glands that secrete hormones and release them directly into the bloodstream hormone – a substance secreted by an endocrine gland that regulates various body functions

The Endocrine Glands Figure 2.14: The Endocrine Glands

Pituitary and the Hypothalamus
Pituitary gland Lies below hypothalamus Labeled as “master gland” Hormones secreted by pituitary gland Hypothalamus regulates pituitary gland activity pituitary gland – the gland that secretes growth hormone, prolactin, antidiuretic hormone, and other hormones Growth hormone – regulates growth of muscles, bones, and glands Prolactin – regulates maternal behavior in lower mammals and stimulates production of milk in women Vasopressin – inhibits production of urine when body fluids are low Oxytocin – stimulates labor in pregnant women, connected with maternal behavior

Pineal Gland Pineal gland Secretes melatonin
Helps regulate sleep-wake cycle May affect onset of puberty

Thyroid Gland Thyroid gland Produces thyroxin
Affects body’s metabolism Hypothyroidism Hyperthyroidism Cretinism Hypothyroidism – Thyroxin deficiency Hyperthyroidism – Too much thyroxin Cretinism – stunted growth and mental retardation Thyroxin deficiency in children

Adrenal Glands Adrenal glands Located above the kidneys
Cortical steroids increase resistance to stress promote muscle development Epinephrine and norepinephrine Helps arouse body in threatening situations Adrenal cortex secretes cortical steroids – increase resistance to stress; promote muscle development; cause liver to release stored sugar; makes more energy available in emergency Adrenal medulla secretes epinephrine and norepinephrine – Helps arouse body in threatening situations

Steroids, Behavior, and Mental Processes
increase muscle mass, heighten resistance to stress, increase body’s energy supply Anabolic steroids enhance athletic prowess connected with self-confidence, aggressiveness, memory function

Testes and Ovaries Testosterone Estrogen and progesterone
produced by testes (smaller amounts from adrenal gland) male sex characteristics Estrogen and progesterone produced by ovaries (smaller amounts from testes) female sex characteristics

Evolution and Heredity: The Nature of Nature
LO4 Describe evolutionary psychology and the connections between heredity, behavior, and mental processes.

Truth or Fiction? Charles Darwin was nearly excluded from the voyage that led to the development of his theory of evolution because the captain of the ship did not like the shape of his nose. Truth or Fiction? Charles Darwin was nearly excluded from the voyage that led to the development of his theory of evolution because the captain of the ship did not like the shape of his nose. TRUE Darwin had volunteered to serve on an expeditionary voyage on the HMS Beagle, but the captain, Robert Fitz-Roy, objected to Darwin because of the shape of his nose. Fitz-Roy believed that you could judge a person’s character by the outline of his facial features and Darwin’s nose didn’t fit the bill. But Fitz-Roy relented, and in the 1830s, Darwin undertook the historic voyage to the Galapagos Islands that led to the development of his theory of evolution.

Truth or Fiction? Charles Darwin was nearly excluded from the voyage that led to the development of his theory of evolution because the captain of the ship did not like the shape of his nose. TRUE! Truth or Fiction? Charles Darwin was nearly excluded from the voyage that led to the development of his theory of evolution because the captain of the ship did not like the shape of his nose. TRUE Darwin had volunteered to serve on an expeditionary voyage on the HMS Beagle, but the captain, Robert Fitz-Roy, objected to Darwin because of the shape of his nose. Fitz-Roy believed that you could judge a person’s character by the outline of his facial features and Darwin’s nose didn’t fit the bill. But Fitz-Roy relented, and in the 1830s, Darwin undertook the historic voyage to the Galapagos Islands that led to the development of his theory of evolution.

Darwin’s Theory of Evolution
Struggle for existence Competition for same resources Natural selection Adaptive genetic variations aid in survival Mutations Sudden changes in genes natural selection – the concept that holds that adaptive genetic variations among members of a species enable individuals with those variations to survive and reproduce mutation – a sudden variation in an inheritable characteristic, as distinguished from a variation that results from generations of gradual selection

The Human Skeleton and the Skeletons of Some Relatives
Figure 2.15: The Human Skeleton and the Skeletons of Some Relatives – The idea that humans were genetically related to monkeys and other animals was so divergent from other 19th-century views of our species that Darwin was initially reluctant to discuss his theory of evolution. The Descent of Man, published in 1871, made the case that humans, like other species, were a product of evolution. Darwin believed that the great apes (chimpanzees, gorillas, and so on) shared a common primate ancestor. We did not descend from Neanderthals but we coexisted with them for thousands of years. Neanderthals became extinct some 35,000 years ago.

Evolutionary Psychology
Ways in which adaptation and natural selection are connected with behavior and mental processes Behavior patterns evolve and can be transmitted genetically from generation to generation Instinctive or species specific behaviors evolutionary psychology – the branch of psychology that studies the ways in which adaptation and natural selection are connected with mental processes and behavior

Evolutionary Psychology
Instinct Stereotyped patterns of behavior that are triggered in a specific situation Species-specific Resists modification, not learned instinct – a stereotyped pattern of behavior that is triggered by a particular stimulus and nearly identical among members of a species, even when they are reared in isolation

Heredity, Genetics and Behavioral Genetics
Transmission of traits from parent to offspring, based on genes Genetics Subfield of biology that studies heredity Behavioral Genetics Focuses on contributions of genes to behavior heredity – the transmission of traits from parent to offspring by means of genes genetics – the area of biology that focuses on heredity

Genes and Chromosomes Gene Chromosomes DNA (deoxyribonucleic acid)
Basic unit of heredity Chromosomes Structure within cell nucleus that carry genes Humans have 46 chromosomes (23 pairs) DNA (deoxyribonucleic acid) Substance that forms chromosomes Double helix – contains genetic code Nucleotides - A and T, C and G gene – a basic unit of heredity, which is found at a specific point on a chromosome chromosome - a microscopic rod-shaped body in the cell nucleus carrying genes that transmit hereditary traits from generation to generation; humans normally have 46 chromosomes DNA – acronym for deoxyribonucleic acid, the substance that forms the basic material of chromosomes; it takes the form of a double helix and contains the genetic code

Cells, Chromosomes, and DNA
Figure 2.16: Cells, Chromosomes, and DNA - A. The nuclei of cells contain chromosomes. B. Chromosomes are made up of DNA. C. Segments of DNA are made up of genes. The genetic code —that is, the order of A, G, T, and C—determines your species and all those traits that can be inherited, from the color of your eyes to predispositions toward many psychological traits and abilities, including sociability and musical talent.

Genes and Chromosomes Genes regulate development of specific traits
Some traits are determined by one gene Other traits are polygenic polygenic – referring to traits that are influenced by combinations of genes

Genes and Chromosomes Genotype Phenotype
Individual’s genetic makeup (nature) Phenotype Actual appearance, based on genotype and environmental influences (nature and nurture) genotype – one’s genetic makeup, based on the sequencing of the nucleotides we term A, C, G, and T phenotype – one’s actual development and appearance, as based on one’s genotype and environmental influences nature – the inborn, innate character of an organism nurture – the sum total of the environmental factors that affect an organism from conception onward

Chromosomes Receive 23 chromosomes from father’s sperm and 23 chromosomes from mother’s egg cell 23rd pair of chromosomes are sex chromosomes XX – female XY – male Down syndrome Chromosomal abnormality sex chromosomes – the 23rd pair of chromosomes, whose genetic material determines the sex of the individual Down syndrome – a condition caused by an extra chromosome on the 21st pair and characterized by mental deficiency, a broad face, and slanting eyes

Down Syndrome Photo: Down syndrome is caused by an extra chromosome on the 21st pair and becomes more likely to occur as the mother’s age at the time of pregnancy increases. Persons with Down syndrome have characteristic facial features including downward-sloping folds of skin at the inner corners of the eyes, are intellectually deficient, and usually have health problems that lead to death by middle age.

Kinship Studies Focus on presence of traits and behavior patterns in people who are, or are not related biologically Twin studies Monozygotic twins Dizygotic twins Adoption studies monozygotic (MZ) twins – twins that develop from a single fertilized ovum that divides in two early in prenatal development; MZ twins thus share the same genetic code; also called identical twins dizygotic (DZ) twins – twins that develop from two fertilized ova and who are thus as closely related as brothers and sisters in general; also called fraternal twins

Chapter 2: Biology and Psychology

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