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Human Heredity Chapter 11.1 & 11.3 RECESSIVE Genetic Disorders • may be passed on to children without “knowing” • both parents are CARRIERS of recessive alleles – Aa x Aa • passed like any recessive trait – offspring must get recessive allele from mother + father – aa Cystic Fibrosis (CF) Albinism Galactosemia Tay Sachs Xeroderma Pigmentosum (XP) Primordial Dwarfism Phenylketonuria (PKU) Cystic Fibrosis (CF) – affects the mucus producing glands, digestive enzymes and sweat glands Cause: • recessive allele that is defective Effects: • excessive mucus production • respiratory system is compromised; high risk of infection • digestive and respiratory system failure • life expectancy 36.8 years Cure/Treatement: • no cure • daily breathing treatments • mucus-thinning drugs • pancreatic enzyme supplements Cystic Fibrosis - http://www.youtube.com/watch?v=PjoE-yzyDNk Albinism – partial or total lack of pigment (melanin) in hair, skin and eyes Cause: • recessive allele that is defective Effects : • do not produce normal amounts of melanin • skin susceptible to UV damage • higher risk of skin cancer and eye damage • occurs in humans and other mammals Cure/Treatment: • no cure • protect eyes and skin from sun Galactosemia – an inability to digest galactose (milk sugar) Cause: • recessive allele that is defective • lack of enzyme that breaks down galactose Effects : • enlarged liver and kidney failure • galactose builds up in the cells and becomes toxic • usually causes no symptoms at birth • if not detected immediately results in liver disease, mental retardation and death Cure/Treatment: • no cure • children diagnosed early can have a normal, healthy life • treatment is the restriction of galactose and lactose from the diet Tay-sachs Disease – an inability to break down fatty acids: only affects people of Jewish descent Cause: • recessive allele that is defective • lack of enzyme that breaks down fatty substances Effects • inability to break down fatty acids • fatty deposits build up in the brain • brain cells deteriorate • mental capacity is diminished • death by age 5 Cure/Treatment • no cure or treatment Xeroderma Pigmentosum (XP) • recessive genetic disorder • inability to repair damage caused by UV light • in extreme cases, all exposure to sunlight must be forbidden, no matter how small • individuals with the disease are often referred to as Children of the Night • suffer from basal cell carcinomas and other skin malignancies (such as malignant melanoma and squamous cell carcinoma) Primordial Dwarfism • recessive genetic disorder • form of dwarfism that results in a smaller body size in all stages of life beginning from before birth • PROPORTIONATE DWARFISM, in which individuals are extremely small for their age, even as a fetus • caused by inheriting a mutant gene from each parent Kenadie - born February 13, 2003 2 lbs 8oz and 11 inches long Phenylketonuria (PKU) • recessive genetic disorder • caused by a mutation in the gene for a liver enzyme called PAH • this enzyme is necessary to metabolize the amino acid phenylalanine Effects of untreated PKU… • children normal at birth but fail to attain early developmental milestones • microcephaly, progressive impairment of mental function seizures, learning disabilities nd other serious medical problems, Cure/Treatment of PKU… • there is no cure • treatment with restricted diet supplemented by amino acids and other nutrients • PKU is commonly included in newborn screenings performed just after birth Tetra-Amelia Syndrome • recessive genetic disorder • rare disorder characterized by the absence of all four limbs • severe malformations of various parts of the body, including the face and head, heart, nervous system, skeleton, and genitalia • most are stillborn or die shortly after birth • Nick Vujicic – Australian Motivational Speaker LOOK AT YOURSELF http://www.youtube.com/watch?v=Gc4HGQHgeFE DOMINANT Genetic Disorders • only need 1dominant allele (AA or Aa) to inherit the disorder • NO CARRIERS • either you have the disorder or you don’t Huntington’s Disease Achondroplasia Progeria Treacher Collins Marfan Syndrome Huntington’s Disease - the genetically programmed degeneration of brain cells Cause: • dominant allele that affects neurological function Effects: • symptoms appear between age 30 - 50 • degeneration of brain cells (neurons) • loss of intellectual faculties • uncontrollable movements • emotional disturbances Cure/Treatment: woman with Huntington’s • none Disease at age 48 Huntington’s - http://www.youtube.com/watch?v=xguyxdmeUK8 Achondroplasia - a common form of dwarfism Cause: • dominant allele that affects bone growth Effects: • short arms and legs • 75 % of individuals with achondroplasia are born to parents of average size… • this means that most cases of achondroplasia occur “out of the blue” and are the result of a new mutation in the gene Cure/Treatment: • none; normal life expectancy Achondroplasia - http://www.youtube.com/watch?v=d8B-rdUrO9U Progeria • extremely rare genetic disease wherein symptoms resembling aspects of aging are manifested at an early age • typically live to their mid teens and early twenties • occurs as a result of a dominant, new mutation • rarely inherited Progeria - http://www.youtube.com/watch?v=T8eaD6FdFJw Treacher Collins • rare, congenital disorder characterized by craniofacial deformities • caused by a defective protein called treacle Physical Features Include …. • downward slanting eyes • micrognathia (a small lower jaw) • conductive hearing loss • absent cheekbones • malformed or absent ears. Cure/Treatment… • No cure - only affects physical features • physical features can be made less obvious by plastic surgery Treacher Collins - http://www.youtube.com/watch?v=tYYMRd39wcE Marfan Syndrome • disoder of connective tissue Effects… • unusually tall, long limbs and long, thin fingers • range of expressions - from mild to severe • defects of the heart valves and aorta, lungs, skeleton, hard palate Cure/Treatment…. • no cure • medications to slow progression of disease • new treatments being developed • life expectancy today - similar to that of the average person Codominant Sickle Cell Anemia Cause: • CODOMINANT ALLELE that is defective • DD = disc shaped; CD = some disc + some crescent; CC = crescent shaped • both mom and dad must be “carriers” of a defective allele Effects: • causes Red Blood Cells to be misshapen – sickle/C/crescent shaped • defective RBCs don’t live long; don’t effectively transport oxygen; are stiff and sticky; block blood flow • cause pain, organ damage, increased risk of infection Cure/Treatment: • bone marrow transplant – finding matching donor is difficult and procedure has risks – may work for some • regular medical care, pain medicine, fluids, oxygen therapy Sickle Cell Anemia - http://www.youtube.com/watch?v=LlF_8oRs6Bw PEDIGREE chart which shows the inheritance of a trait from one generation to the next Allows geneticists to trace the transmission of a trait through a family. square = male circle = female colored shape = has trait half colored shape = carrier slash = deceased How many generations are represented? How many males? afflicted males? normal males? How many females? afflicted females? normal females? Any carriers? Sex-linked or autosomal trait? Dominant or recessive trait? Any twins? deceased individuals? Queen Victoria… • born 1819…..became Queen of England in 1837 • married her 1st cousin Prince Albert (of Germany) in 1840 • this was the custom – royalty would not marry a commoner • was a carrier of HEMOPHILIA • had 9 children and passed HEMOPHILIA ON TO SEVERAL OF THEM • all of her children married into the ROYAL FAMILIES OF EUROPE • hemophilia became known as THE ROYAL DISEASE Granddaughter Of Queen Victoria … Princess Alexandria Victoria… born in 1872 o was also a CARRIER OF HEMOPHILIA o in 1890 she married her 2nd cousin, Nicholas Romanov II, the Tsar of Russia Tsar (Nicholas) and Tsarina (Alexandria) of Russia had 5 children… 4 GIRLS - Olga, Tatiana, Maria, Anastasia 1 BOY - Alexei - heir to the Russian throne - had HEMOPHILIA 1918 - Russian Civil War • Tzar Nicholas II, his wife and the 5 children disappeared • there were many theories surrounding their disappearance Nat Geo – Mystery of the Romanovos – 4 min http://www.youtube.com/watch?v=g_JFNH_PDgo • 1991 - the remains of Tzar Nicholas, his wife, and 3 of the children were found and exhumed for DNA testing • the bodies of Alexi and 1 of his sisters was missing…. HUMAN CHROMOSOMES Human somatic cells contain…. 46 individual chromosomes or 23 chromosome pairs Of these 23 pairs… SEX CHROMOSOMES (1 pair) • determine the sex of an individual AUTOSOMES (22 pairs) • do not determine the sex of an individual KARYOTYPE photomicrograph of the chromosomes in a dividing cell chromosomes are grouped and placed into (23)pairs female - 46 XX male - 46 XY nonhomologous Telomeres protective caps on ends on chromosomes made of protein and DNA may play a role in cancer and aging telomeres are like… aglets on the ends of a shoe string Mutations What is a mutation? a change in the DNA it is interesting that mutations can be helpful, harmful or may have no effect mutations – are a source of genetic variation in LT Mutations What causes a mutation? a mutagen ….anything that can cause a change in the DNA Some mutagens are…. viruses, chemicals, toxins, UV light,…. Mutations can also happen as a result of … DNA being copied incorrectly Types of Mutations SOMATIC cell mutations - affect body (somatic) cells will affect individual, but not offspring GERM cell mutations - affect germ (sex) cells will affect offspring, but not the individual LETHAL mutations will cause death either before or shortly after birth Types of Chromosome Mutations Deletion – A piece of a chromosome is LOST Inversion – A piece of a chromosome breaks off, FLIPS OVER + REATTACHES Translocation – A piece of a chromosome breaks off and attaches to ANOTHER chromosome Nondisjunction – Homologues DO NOT SEPARATE PROPERLY DURING CELL DIVISION - results in too many or too few chromosomes loss of a portion of a chromosome Williams Syndrome DELETION • caused by spontaneous deletion of genes on chromosome 7 • rare, neurodevelopmental disorder • characterized by, "elfin" facial appearance, low nasal bridge, cheerful demeanor and ease with strangers • developmental delays and cardiovascular problems Inversion – a section of a chromosome breaks off, flips over and reattaches Translocation – a portion of a chromosome detaches and reattaches to a nonhomologous chromosome Let’s Practice – What type of mutation? NONDISJUNCTION - when chromosomes don’t separate properly during CELL DIVISION (CAN OCCUR IN MITOSIS or MEIOSIS) nondisjunction means “not coming apart” Nondisjunction in Meiosis… leads to … monosomy (45) – missing a chromosome of a pair (having only 1 chromosome of the pair) trisomy (47) – having an extra chromosome in a pair (having 3 chromosomes in the pair) Conditions resulting from Nondisjunction • • • • Down’s Syndrome Turner’s Syndrome Klinefelter’s Syndrome Jacob’s Syndrome Down Syndrome (monosomy) male or female having an extra chromosome in pair #21 • (3 chromosomes instead of 2) - 47 XX or 47 XY • nondisjunction on #21 = Trisomy 21 Down Syndrome NONDISJUNCTION male or female having an extra chromosome in pair #21 (3 chromosomes instead of 2) - 47 XX or 47 XY • almond shaped eyes; flat nose bridge; large tongue • ears are set lower on the head • shorter in stature • simean crease on the palm of the hand • possible congenital heart defects • flat feet, sandal toe (large gap between big toe and the next) • lower IQ and developmental delays Turner Syndrome (Monosomy) • female missing a sex chromosome; 45 XO • nondisjunction on #23; monosomy Klinefelter Syndrome (Trisomy) • male having an extra sex chromosome • 47 XXY or 48 XXXY; nondisjunction on #23; trisomy Jacob’s or XYY Syndrome (Trisomy) • male having an extra Y (sex) chromosome • 47 XYY; nondisjunction on #23; trisomy • clinical phenotype is normal Fetal (genetic)Testing – pre-pregnancy: DNA testing & genetic counseling – post-pregnancy: PKU testing – during pregnancy: • Amniocentesis • Chorionic Villi Sampling (CVS) • Fetal Blood Sampling Amniocentesis - a small amount of amniotic fluid (containing fetal tissues and cells) is extracted from the amniotic sac surrounding the developing fetus - the DNA is examined for genetic abnormalities Chorionic Villi Sampling (CVS) - the removal of a small piece of the placenta (chorionic villi) during early pregnancy to screen for genetic defects – the placenta has the same genetic makeup as the fetus Fetal Blood Sampling (FBS) - the collection of fetal blood from the umbilical cord or fetus – the blood is tested genetic defects or other abnormalities