Unit 11: Inheritance Patterns of Human Traits

Simple Autosomal Recessive

• TT-normal
• Tt-carrier
• tt-affected
• Albinism
• a defect of the gene that results in the absence of the pigments such as melanin
• pale skin, eye conditions, sensitive to the sun

• Cystic Fibrosis
• thick mucus in the lungs and digestive track
• one of the most common genetic disease in white Americans
• can be treated with physical therapy, special diets, drug therapies, and gene therapy

• Phenlyketonuria (PKU)
• caused by a missing enzyme that is needed to break down fats 
• can cause severe mental retardation but all babies in U.S. are tested soon after birth
•  Children that have this disease must have a special diet that does not have phenylalanine in it until they reach around 5 or 6
• Hereditary Deafness (Otosclerosis)
• Hitchhiker's Thumb

• Tay-Sachs
• Common in Jewish people
• this disease is caused by a missing enzyme that breaks down a lipid produced and stored in the tissues of the central nervous system
• The child dies by the age of 2 or 3
• no cure

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Simple Autosomal Dominant

• TT, Tt-affected
• tt-normal
• No carriers
• Tongue Rolling

• Huntington's Disease
• the tissue in the middle of the brain begins to die
• symptoms begin between ages of 30-50
• these people lose control of their muscles.
• Cataracts
• the clouding of the lens of the eye
• Polydactyly (extra fingers or toes)
• Common - 1 in every 800 births
• See http://www.examiner.com/article/here-comes-honey-boo-boo-niece-s-duplicate-thumb-likely-caused-by-mutant-gene

• Achondroplasia (dwarfism)

Autosomal Dominant and Autosomal recessive Diseases:

• Some diseases are carried by dominant alleles (B), some are carried by recessive alleles (b).
• If the disease is carried by a dominant alleles, then the offspring need only inherit one allele to express the disease (BB or Bb).
• If the disease is carried by a recessive allele, then the offspring needs two recessive alleles to express the disease (bb).
• If a person has just one defective gene (Bb), then the person is known as a carrier. They will not express the disease but can pass it to their offspring. Only recessive alleles can be carried.

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Codominant Autosomal Recessive

• Sickle-Cell Anemia
• red blood cells are abnormal (have a crescent shape) blocking small blood vessels causing pain and anemia (low red blood cell count)
• pain, lethargy, anemia, organ failure, stroke
• common in African Americans
• TT-normal
• Tt-shows both normal and sickle cells - has few symptoms, however
• tt-all sickle cells

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Sex-Linked Recessive (Carried on the X Chromosome)

• XcXc, XcY-affected
• XCXc-carrier, not affected
• XCXC, XCY-normal
• Colorblindness
• total or partial loss of ability to distinguish colors
• Hemophilia
• a disorder in which the blood does not clot properly
• Muscular Dystrophy
• the muscles atrophy (become smaller and no longer function properly)
• causes muscle weakness and loss of muscle tissue, which get worse over time

• Icyhyosis Simplex (dry, scaly skin)

Polygenic (Controlled by more than one gene)

• Skin, Hair, Eye color
• Foot size
• Nose length
• Height

Multiple Alleles (More than two alleles available in the gene pool)

• ABO Blood Groups
• Rh Blood Factor

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Chromosome Problems

Nondisjunction

Down Syndrome (Trisomy 21; Mongolism)

• An extra chromosome of the 21st pair
• Caused by nondisjunction
• Mentally retarded
• Slanted Eyes
• Large, thick tongue
• Poor muscle tone
• Abnormal palm and foot prints
• Usually overweight

Kleinfelter Syndrome

• An extra X chromosome (XXY)
• Male
• Tall and thin
• Mentally retarded
• Abnormal breast tissue
• Caused by nondisjunction
• May appear normal
• Sterile

Turner's Syndrome

• Monosomy - missing X chromosome (X_)
• Caused by nondisjunction
• Immature sexual characteristics
• Mentally Retarded
• Sterile

• Linda Hunt of NCIS Los Angeles

Super Female; Triple X (XXX)

• Caused by nondisjunction
• Female
• An extra X chromosome (XXX)
• Good Athelete
• Mentally retarded to a certain extent

• Ewa Klobukowska, a 1964 Olympic sprint bronze medalist who was the first woman to fail the sex chromosome test during the 1967 European Cup. “One chromosome too many to be declared a woman for the purposes of athletic competition” was the statement, and she was obliged to return all her medals. She gave birth to a baby the following year. 
• Also see a 2006 case: http://espn.go.com/olympics/story/_/id/8192977/failed-gender-test-forces-olympian-redefine-athletic-career-espn-magazine

Jacob's Syndrome (XYY)

• Caused by nondisjunction
• Male over six feet tall
• Persistent acne
• Speech problems
• Delayed maturity
• Extremely aggressive*
• High percentage are criminally insane

XXXY

• Caused by nondisjunction)
• Male
• Infertile
• Extremely agressive* behavior problems
• High Voice

XXYY

• Male
• 48 Chromosomes
• See: http://xxyysyndrome.org/main/

Fragile X Syndrome

• caused by a gene mutation on the X chromosome (the expansion or lengthening of the FMR1 gene)
• When the gene lengthens it switches off production of a protein that is involved in brain development and other functions
• Usually severely affects males more than females
• mental retardation

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Missing Pieces of Chromosomes

Prader-Willi Syndrome

• part of chromosome 15 is missing, intellectual disability is common

Wolf-Hirschhorn Syndrome

• part of chromosome 4 is missing
• Children with this syndrome have profound intellectual disability

Cri du chat syndrome (cat's cry syndrome)

• part of chromosome 5 is missing
• heart defects are common

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Detecting Genetic Disorders

• Amniocentesis is removing and testing a sample of amniotic fluid (the liquid that surrounds a fetus).
• Karyotype

• Can see if there are the correct number of chromosomes
• Ultrasound (sonogram) is using sound waves to determine the position and anatomy of the offspring.
• Fetoscopy is the direct observation of the fetus and surrounding tissues.

***FYI: The term intellectual disability is now used instead of mental retardation.