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Bell Ringer10.21.2011  Name a part of your brain that you remember reading about and write down anything you remember about it (e.g. where it’s located,

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Presentation on theme: "Bell Ringer10.21.2011  Name a part of your brain that you remember reading about and write down anything you remember about it (e.g. where it’s located,"— Presentation transcript:

1 Bell Ringer  Name a part of your brain that you remember reading about and write down anything you remember about it (e.g. where it’s located, it’s function, etc.).

2 Unit 3: Biological Bases of Behavior AP PsychologyMs. Desgrosellier

3 Neuropsychologists:  psychologists who explore the relationships between brain/nervous systems and behavior.  aka: biological psychologists, biopsychologists, behavioral geneticists, physiological psychologists, and behavioral neuroscientists.

4 ORGANIZATION OF YOUR NERVOUS SYSTEM  All of the neurons in your body are organized into your nervous system.  The two major subdivisions are the central nervous system and the peripheral nervous system.

5 ORGANIZATION OF YOUR NERVOUS SYSTEM  Central Nervous System (CNS): made up of the brain and spinal cord.  Spinal cord: starts at the base of your back and extends upward to the base of your skull where it joins your brains.  Made mainly of interneuron’s and glial cells, which are all bathed by cerebrospinal fluid produced by your glial cells.

6 ORGANIZATION OF YOUR NERVOUS SYSTEM  Peripheral Nervous System (PNS): made up the somatic and autonomic nervous systems, and spread around your body from your spinal cord outwards.  Somatic Nervous System: motor neurons that stimulate skeletal (voluntary) muscle.  Autonomic Nervous System: motor neurons that stimulate smooth (involuntary) and heart muscle.

7 ORGANIZATION OF YOUR NERVOUS SYSTEM  The Autonomic Nervous System is divided into two parts:  Sympathetic Nervous System: Responses that help your body deal with stressful events, including:  Dilation of pupils, release of glucose from your liver, dilation of bronchi, inhibition of digestive functions, acceleration of heart rate, secretion of adrenalin from your adrenal glands, acceleration of breathing rate, and inhibition of secretion of your tear glands.

8 ORGANIZATION OF YOUR NERVOUS SYSTEM  The Autonomic Nervous System is divided into two parts:  Parasympathetic Nervous System: Calms your body following sympathetic stimulation by restoring digestive processes (salivation, peristalsis, enzyme secretion), returning pupils to normal size, stimulating tear glands, restoring normal bladder contractions, slow breathing and heart rate, etc.

9 ORGANIZATION OF YOUR NERVOUS SYSTEM  Turn to your neighbor and explain the two major subdivisions of the nervous system.  What are the 2 parts of the CNS?  What are the 2 parts of the PNS?  What are the 2 parts of the autonomic NS?

10 Nervous System Peripheral Nervous System Central Nervous System Spinal Cord Autonomic Nervous System Somatic Nervous System Sympathetic Nervous System Parasympathetic Nervous System Brain

11 STRUCTURE AND FUNCTION OF THE NEURON  neuron: the basic unit of structure and function of your nervous system.  three major functions:  receive information, process it, and transmit it to the rest of your body.

12 STRUCTURE AND FUNCTION OF THE NEURON  glial cells: guide the growth of developing neurons, help provide nutrition for and get rid of wastes of the neuron, and form an insulating sheath around neurons that speeds conduction.

13 STRUCTURE AND FUNCTION OF THE NEURON  cell body (cyton or soma): contains cytoplasm and the nucleus, which directs synthesis of neurotransmitters.

14 STRUCTURE AND FUNCTION OF THE NEURON CELL BODY

15 STRUCTURE AND FUNCTION OF THE NEURON  dendrites: branching tubular processes capable of receiving information.  axon: emerges from the cyton as a single conducting fiber (longer than a dendrite) which branches.

16 STRUCTURE AND FUNCTION OF THE NEURON CELL BODY DENDRITES AXON

17 STRUCTURE AND FUNCTION OF THE NEURON  terminal button (axon terminal or synaptic knob): tip of the axon.  myelin sheath: fatty tissue created by glial cells that insulate the axon and speeds up transmission.

18 STRUCTURE AND FUNCTION OF THE NEURON CELL BODY DENDRITES AXON MYELIN SHEATH AXON TERMINAL

19 STRUCTURE AND FUNCTION OF THE NEURON  nucleus: holds all the genetic information of the cell.  node of Ranvier: gaps between the myelin sheaths.  Schwann’s cells: cells that create myelin.

20 STRUCTURE AND FUNCTION OF THE NEURON CELL BODY DENDRITES AXON MYELIN SHEATH AXON TERMINAL NUCLEUS SCHWANN’S CELLS NODE OF RANVIER

21 STRUCTURE AND FUNCTION OF THE NEURON  neurogenesis: growth of new neurons that takes place throughout life.

22 Bell Ringer  Sketch out the nervous system “tree” and briefly explain each section.  HAVE YOUR NEURON HOMEWORK OUT TO BE CHECKED.

23 Nervous System Peripheral Nervous System Central Nervous System Spinal Cord Autonomic Nervous System Somatic Nervous System Sympathetic Nervous System Parasympathetic Nervous System Brain

24 STRUCTURE AND FUNCTION OF THE NEURON CELL BODY DENDRITES AXON MYELIN SHEATH AXON TERMINAL NUCLEUS SCHWANN’S CELLS NODE OF RANVIER

25 STRUCTURE AND FUNCTION OF THE NEURON  neurotransmitters: chemicals stored in structures of the terminal buttons called synaptic vesicles.  Used by neurons to communicate with each other.

26 STRUCTURE AND FUNCTION OF THE NEURON  Synapse: the gap between neurons where neurotransmitters are released to attach to specific receptor sites on membranes of dendrites of your postsynaptic neurons.  This is called the “lock and key concept” because each neurotransmitter has a specific match on the dendrites, like a key fitting into a lock.

27 STRUCTURE AND FUNCTION OF THE NEURON

28  IN YOUR NOTES, create a 4 column table to fill out (we will add rows together) NeurotransmitterFunctionToo Much:Too little:

29 NEUROTRANSMITTERS  e.g. acetylcholine (ACh) causes contraction of skeletal muscles, helps regulate heart muscles, is involved in memory, and also transmits messages between the brain and spinal cord.  Lack of ACh is associated with Alzheimer’s disease.

30 NEUROTRANSMITTERS NeurotransmitterFunctionToo Much:Too little: acetylcholine (ACh) muscle movement, memory, messages between brain & spinal cord n/aAlzheimer’s disease

31 NEUROTRANSMITTERS  dopamine: stimulates the hypothalamus to synthesize hormones and affects alertness and movement.  Lack of dopamine is associated with Parkinson’s disease.  Too much is associated with schizophrenia.

32 NEUROTRANSMITTERS  glutamate: excitatory neurotransmitter involved in information processing throughout the cortex and especially memory formation in the hippocampus.  Both schizophrenia and Alzheimer’s may involve glutamate receptors.

33 NEUROTRANSMITTERS  Serotonin: associated with sexual activity, concentration and attention, moods, and emotions.  Lack of serotonin is associated with depression.

34 NEUROTRANSMITTERS  endorphins: opioid peptide, considered the brain’s own pain killers.

35 NEUROTRANSMITTERS  Gamma-aminobutyric acid (GABA): inhibits the firing of neurons.  Valium and anticonvulsant drugs increase activity of GABA.  Huntington’s disease is associated with insufficient GABA-producing neurons in parts of the brain involved in the coordination of movement.  Seizures are associated with malfunctioning GABA systems.

36 NEUROTRANSMITTERS  Other chemicals, like drugs, can interfere with the action of neurotransmitters.  Agonists may mimic a neurotransmitter and bind to its receptor site to produce the effect of the neurotransmitter.  Antagonists: block a receptor site inhibiting the effect of the neurotransmitter or agonist.

37 Neuron Functions  All behavior begins with the actions of your neurons.  A neuron gets incoming information from its receptors spread around its dendrites.  The info is then sent to the cell body, where it’s combined with other incoming information.  Neural impulses are electrical in nature along the neuron.

38 Neuron Functions  The neuron at rest is more negative inside the cell membrane relative to outside the membrane.  The neuron’s resting potential results from the selective permeability of its membrane and the presence of electrically charged particles called ions near the inside and outside surfaces of the membrane in different concentrations.

39 Bell Ringer  Choose two neurotransmitters and briefly describe them (include their function, and what happens if there’s too much or too little of it).

40 Neuron Functions  When sufficiently stimulated (to threshold), a net flow of sodium ions into the cell causes a rapid change in potential across the membrane, known as action potential.

41 Neuron Functions  If your stimulation is not strong enough, your neuron does not fire.  The strength of the action potential is constant whenever it occurs.  This is called the “all-or-none principle.”

42 Neuron Functions  The wave of depoloarization and repolarization is passed along the axon to the terminal buttons, which release neurotransmitters.  Spaces between segments of myelin are called nodes of Ranvier.  Saltatory conduction: When the axon is myelinated, conduction speed is increased since depolarizations jump from node to node.

43 Neuron Functions  Neurotransmitters are released into the synapse.  Some synapses are excitatory, meaning the neurotransmitters cause the neuron on the other side to generate an action potential (to fire).  Other synapses are inhibitory, reducing or preventing neural impulses.

44 Neuron Functions  The sum of all excitatory and inhibitory inputs determines whether your next neuron will fire and at what rate.  The constant flow of neurotransmitters regulates metabolism, temperature, and respiration.  It also enables you to learn, remember, and decide.

45 Neuron Functions  reflex: simplest form of behavior, involving impulse conduction over a few neurons.  The path across maybe three neurons is called a reflex arc.  Afferent neurons: sensory neurons that transmit impulses from your sensory receptors to the spinal cord or brain.  Interneurons: located entirely in your brain and spinal cord, intervene between sensory and motor neurons.

46 Neuron Functions  Efferent neurons: motor neurons transmit impulses form your sensory or interneurons to muscle cells that contract or gland cells that secrete.  Effectors: muscle and gland cells.

47 Neuron Functions  Examples of reflexes:  pupillary, knee jerk, sneezing, and blinking.  Neural impulses: dendrites  to cell bodies  axons  terminal buttons  neurotransmitters  synapse  among neurons from the receptor to the effector.

48 TECHNIQUES TO LEARN ABOUT STRUCTURE & FUNCTION  Clinical Observation (Case Study)  Look at injuries, diseases, etc.

49 TECHNIQUES TO LEARN ABOUT STRUCTURE & FUNCTION  Over 150 years ago people were studying patients with brain damage and linked loss of structure with loss of function.  Essentially losing brain tissue caused brain damage.

50 TECHNIQUES TO LEARN ABOUT STRUCTURE & FUNCTION  Phineas Gage was a level-headed, calm foreman of a railroad crew in  An explosion shot an iron rod through his head, severing the connections between his limbic system and his frontal cortex.  Gage became hostile, impulsive, and unable to control his emotions or his obscene language.  Autopsy revealed that the relationship between frontal lobes and control of emotional behavior.

51 Who is Phineas Gage?

52 Broca’s area  Paul Broca (1861) did an autopsy on a patient named Tan, who couldn’t speak even though there was no physical damage and he could understand language.  Tan’s brain showed loss of tissue in part of the frontal lobe of the left central cerebral hemisphere (as did several other similar cases).

53 Broca’s area  It was concluded that damage to this so-called Broca’s area caused a loss of ability to speak, known as expressive aphasia.

54 Wernicke’s area  Carl Wernicke found another brain area involved with understanding language in the left temporal lobe.  Destruction of Wernicke’s area results in loss of ability to comprehend written and spoken language, known as receptive aphasia.

55 DO NOW:  Briefly explain who Phineas Gage was and why he is important to Psychology.

56 Lesions  Precise destruction of brain tissue.  Enabled more systematic study of the loss of function resulting from surgical removal, cutting of neural connections, or destruction by chemical applications.

57 Lesions  E.g. Surgery to relieve epilepsy cuts neural connections at the corpus callosum, between cerebral hemispheres.  Studies of patients with “split brains” have shown that the left and right hemispheres do not perform exactly the same functions.

58 Bell Ringer  In your own words, briefly explain how an action potential happens and how a message is passed along a neuron.

59 Right hemisphere:  nonverbal  spatial, musical, and holistic functions  identifying faces  recognizing emotional facial expressions

60 Left hemisphere:  verbal functions  mathematical functions  analytical functions  language

61 Manipulating the brain  Scientists can electrically, chemically, or magnetically stimulate various parts of the brain and note effects.  Researchers have electrically stimulated different cortical areas of the brain during surgery.

62 Manipulating the brain  It has enabled scientists to observe results, like:  the frontal cortex at particular sites caused body movement for different body parts enabling mapping of the motor cortex.  New research has found that you can magnetically lesion parts of the brain (temporary and so far has shown no harm)

63 DO NOW  Tell me at least three functions of the left hemisphere and three functions of the right hemisphere of the brain.

64 Brain Imaging  Computerized axial tomography (CAT or CT): two-dimensional x-ray slices that are passed through various angles of the brain, arranged to show the extent of a lesion.

65 Brain Imaging  magnetic resonance imaging (MRI): a technique that uses magnetic fields and radio waves to produce computer-generated images that distinguish among different types of soft tissue; allows us to see structures within the brain.

66 Brain Imaging  Putting one’s head into a strong magnetic field aligns the spinning atoms.  A pulse of a radio wave disorients the atoms briefly.  When the atoms return to their normal spin, they release signals that give us a detailed image of the body.

67 Measuring brain function  Scientists can stick a tiny microelectrode into a single neuron to measure its activity.

68 Measuring brain function  electroencephalogram (EEG): an amplified recording of the waves of electrical activity that sweep across the brain’s surface. These waves are measured by electrodes placed on the scalp.

69 Measuring brain function  The amplified tracings are called evoked potentials when the recorded changes in voltage results from a response to a specific stimulus presented to the subject.  Repeated study of the read- out can help researchers filter out brain activity and find the electrical wave caused by the specific stimulus.

70 Measuring brain function  functional magnetic resonance imaging (fMRI): a technique for revealing blood flow and, therefore, brain activity by comparing successive MRI scans. MRI scans show brain anatomy; fMRI scans show brain functions.

71 Measuring brain function  Researchers compare images taken less than a second apart, they can see which parts of the brain “light up” with increased blood flow.

72 Measuring brain function  positron emission tomography (PET) scan: a visual display of brain activity that detects where a radioactive form of glucose goes while the brain performs a given task.

73 Measuring brain function  Active neurons hog the glucose (the brain’s chemical fuel), and the PET scan tracks where in the brain the radioactive glucose goes.

74 Measuring brain function  Researchers can have participants think about certain topics or do activities to see where the glucose goes (thereby showing what part of the brain is active during that activity).

75 The Brain  Covered by protective tissue called meninges and housed in your skull.  The evolutionary perspective studies how the human brain has evolved. One theory breaks the brain into three sections:  The reptilian brain is similar to the brainstem in humans, and is responsible for maintaining homeostasis and instinctive behavior.

76 The Brain  The old mammalian brain roughly corresponds to the limbic system that controls emotional behavior, memory, and vision.  The new mammalian brain or cerebral cortex, accounts for 80% of the brain’s volume and is associated with higher functions of judgment, decision-making, abstract thought, foresight, hindsight, and insight.

77 The Brain  The surface of the cortex has peaks (gyri) and valleys (sulci), which form convolutions that increase the surface area of your cortex.  Deeper valleys are called fissures.

78 The Brain  The last evolutionary development of the brain is localization of functions on different sides of your brain.

79 LOCALIZATION AND LATERALIZATION OF THE BRAIN’S FUNCTION  Association areas: regions of the cerebral cortex that do not have specific sensory or motor functions, but are involved in higher mental functions, such as thinking, planning, remembering, and communicating.

80 LOCALIZATION AND LATERLIZATION OF THE BRAIN’S FUNCTION  Contralaterality: control of one side of your body by the opposite side of your brain.  The left side of your brain controls the right side of your body.  The right side of your brain controls the left side of your body.

81 Bell Ringer  In your own words, briefly describe the different functions of each hemisphere of the brain.

82 Structure of Brain: Brainstem  medulla: where most fibers cross above the brain stem, resulting in contralateral (opposite side) control.  regulates heart rate, blood flow, breathing, digestion, vomiting.

83 Structure of Brain: Brainstem  pons: right above the medulla, helps coordinate movement, and is the bridge between cerebral hemispheres and both medulla and cerebellum.

84 Structure of Brain: Brainstem  reticular formation: a nerve network in the brainstem (pons) that plays an important role in controlling arousal.

85 Structure of Brain  cerebellum: coordinates motor function integrating motion and positional information from the inner ear and muscles.  helps maintain balance.

86 Structure of Brain  basal ganglia (basal nuclei): links the thalamus with the motor cortex and other motor areas.  regulates initiation of movements, balance, eye movements, and posture.  Involved in reward/punishment learning and focus.  Some nuclei (neural clusters) involved in emotion.

87 Structure of Brain  thalamus: relay “station” for sensory pathways carrying visual, auditory, taste, and somatosensory information to/from appropriate areas of cerebral cortex.  Located at the top of the brain stem.

88 Structure of Brain  hypothalamus: controls autonomic functions such as body temperature and heart rate via control of sympathetic and parasympathetic centers in the medulla.  Sets appetite drives (e.g. thirst, hunger, sexual desire) and behavior.

89 Structure of Brain  hypothalamus:  Integrates with endocrine system by secretion of hormones that regulate hormones from the pituitary.  Helps determine biological rhythms.

90 Structure of Brain  amygdala: influences aggression and fear. Coordinates fight-or-flight response.  important in formation of sensory memory.

91 Structure of Brain  hippocampus: Enables formation of new long- term memories.

92 Structure of Brain  cerebral cortex: receives and processes sensory information and directs movement.  Center for higher order process such as thinking, planning, judgment.

93 Structure of Brain  Frontal lobe: Motor cortex strip just in front of somatosensory cortex initiates movements and integrates activities of skeletal muscles.  Contralateral: right/left hemisphere controls other side of body.

94 Structure of Brain  Frontal lobe:  Includes Broca’s area: in left frontal lobe controls production of speech.  Interpret and control emotional behaviors, make decisions, carry out plan.

95 DO NOW  In your own words, briefly describe the following parts of the brain (including the function):  cerebellummedulla  ponsamygdalathalamus  hypothalamus

96 Structure of Brain  Temporal lobes: center for hearing.

97 Structure of Brain  Temporal Lobe:  Includes Wernicke’s area: in left temporal lobe, plays role in understanding language and making meaningful sentences.

98 Structure of Brain  Temporal Lobe:  Right temporal lobe important for understanding music/tonality.  Sound from both ears is processed mostly contralaterally.

99 Structure of Brain  Smell processed near front of temporal lobes.

100 Structure of Brain

101  Plasticity: when one region of the brain is damaged, the brain can reorganize to take over its function.  e.g. phantom limb syndrome

102 DOW NOW  Briefly explain how a signal travels from neuron to neuron.  What is the “all-or-none” principle?

103 Bell Ringer  Choose two parts of the brain and briefly describe their function.

104 THE ENDOCRINE SYSTEM  endocrine system: consists of glands that secrete chemical messengers called hormones in your blood.  Hormones travel to target organs where they bind to specific receptors.

105 THE ENDOCRINE SYSTEM  Pineal gland: produces melatonin that helps regulate circadian rhythms and is associated with seasonal affective disorder.

106 THE ENDOCRINE SYSTEM  pituitary gland: Sometimes called the “master gland” because it produces stimulating hormones that promote secretion by other glands including:  TSH: thyroid-stimulating hormone  ACTH: adrenocorticotropic hormone stimulates adrenal cortex

107 THE ENDOCRINE SYSTEM  pituitary gland:  FSH: stimulates egg or sperm production  Produces ADH (antidiuretic hormone) to help retain water in your body and HGH (human growth hormone).

108 THE ENDOCRINE SYSTEM  Thyroid gland: produces thyroxine, which stimulates and maintains metabolic activities.  Lack of thyroxine in children can result in mental retardation.

109 THE ENDOCRINE SYSTEM  Parathyroids: Produce parathyroid hormone that helps maintain calcium ion level in blood necessary for normal functioning of neurons.

110 THE ENDOCRINE SYSTEM  adrenal glands: adrenal cortex, the outer layer, produces steroid hormones such as cortisol, which is a stress hormone.  Adrenal medulla, the core, secretes adrenaline (epinephrine) and noradrenaline (norepinephrine), which prepare the body for “fight or flight,” like the sympathetic nervous system.

111 THE ENDOCRINE SYSTEM

112  Pancreas: insulin and glucagon regulate blood sugar that fuels all behavioral processes.  Imbalances result in diabetes and hypoglycemia, respectively.

113 THE ENDOCRINE SYSTEM  Ovaries and testes: gonads in females and males respectively, necessary for reproduction and development of secondary sex characteristics.

114 DO NOW  Explain the four lobes of the brain.

115 GENETICS & EVOLUTIONARY PSYCHOLOGY  nature-nurture controversy: the debate about whether your behavior is determined by your heredity or history/environment.

116 GENETICS & EVOLUTIONARY PSYCHOLOGY  Evolutionary psychologists: study how natural selection favored behaviors that contributed to survival and spread of our ancestors’ genes, and may currently contribute to our survival into the next generations.  They look at behaviors that are universal shared by all people.

117 GENETICS & BEHAVIOR  behavioral geneticists: study the role played by our genes and our environment in mental ability, emotional stability, temperament, personality, interests, etc.  They look at the causes of our individual differences.  They believe that genes predispose our behavior.

118 GENETICS & BEHAVIOR  Twin studies are used to study the contributions of heredity and environment.  identical twins: two individuals who share all the same genes/heredity because they develop from the same fertilized egg or zygote.  a.k.a. monozygotic twins

119 GENETICS & BEHAVIOR  fraternal twins: siblins that share about half of the same genes because they develop from two different fertilized eggs or zygotes.  a.k.a. dizygotic twins

120 GENETICS & BEHAVIOR  Heritability: the proportion of variation among individuals in a population that is due to genetic causes.  Schizophrenia and general intelligence are more similar in monozygotic twins are behaviorally more similar than dizygotic twins.

121 GENETICS & BEHAVIOR  Heritability:  If monozygotic twins are separated at birth and raised in different environments (adoption studies), behavioral differences may reveal the contribution of environment to behavior; similarities may reveal the contribution of heredity.

122 GENETICS & BEHAVIOR  Adoption studies assess genetic influence by comparing resemblance of adopted children to both their adoptive and biological parents.  The children must have been adopted as infants without contact with their biological parents.

123 GENETICS & BEHAVIOR  Adoption studies  If the children resemble their biological parents, but not their adoptive families, with respect to a given trait, researchers infer a genetic component for that trait.  Alcoholism, schizophrenia, and general intelligence have shown both genetic and environmental components.

124 Transmission of Hereditary Characteristics  Heredity characteristics are passed down by biological process.  Each DNA segment of a chromosome that determines that determines a trait is a gene.  Chromosomes carry information stored in genes to new cells during reproduction.

125 Transmission of Hereditary Characteristics  Normal human body cells have 46 chromosomes, except for eggs and sperms that have 23 chromosomes.  Males have 44 chromosomes, plus X and Y.  Females have 44 chromosomes, plus X and X.

126 Transmission of Hereditary Characteristics  At fertilization, 23 chromosomes from the sperm unite with 23 chromosomes from the egg to form a zygote with 46 chromosomes.  If the male contributes a Y chromosome, the baby is male.  Fertilization with the wrong amount of chromosomes results in an individual with chromosomal abnormalities.

127 Transmission of Hereditary Characteristics  Turner Syndrome: girls with only one X chromosome (XO) who are short, often sterile, and have difficulty calculating.

128 Transmission of Hereditary Characteristics  Klinefelter’s syndrome: males with an XXY zygote. They lack male secondary sex characteristics at puberty, develop breast tissue, and tend to be passive.

129 Transmission of Hereditary Characteristics  Down syndrome: individuals with three copies of chromosome-21. They are typically mentally retarded and have a round head, a flat nasal bridge, a protruding tongue, small round ears, a fold in the eyelid, and a poor muscle tone and coordination.

130 Transmission of Hereditary Characteristics  genotype: the genetic makeup for a trait of an individual.  phenotype: the expression of the genes.

131 Transmission of Hereditary Characteristics  homozygous gene: the condition when both genes for a trait are the same.  heterozygous: also called hybrid, the condition when genes for a trait are different.  dominant gene: the expressed heterozygous gene.  recessive gene: a gene that is hidden or not expressed when the genes for a trait are different.

132 Transmission of Hereditary Characteristics  Tay-Sachs syndrome: caused by a recessive gene and can result in progressive loss of nervous function and death in a baby.  Albinism: recessive trait that produces lack of pigment and involves quivering eyes and inability to perceive depth with both eyes.

133 Transmission of Hereditary Characteristics  Phenylketonuria (PKU): a recessive trait that results in severe, irreversible brain damage unless the baby is fed a special diet low in phenylalanine within 30 days of birth.  Huntington’s disease: a dominant gene defect that involves degeneration of the nervous system characterized by tremors, jerky motions, blindness, and death.

134 Transmission of Hereditary Characteristics  Sex-linked traits: recessive genes located on the X chromosome with no corresponding gene on the Y chromosome, which result in expression of recessive trait more frequently in males.  e.g. color blindness: sex-linked trait with which individual cannot see certain colors, most often red and green.


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