Human Heredity Chap 11 Lab Biology Mrs. Moon

Human Genetics Human chromosome # = 46 Human nucleotide pairs of DNA = 6 billion Gametes – reproductive cells Zygote – fertilized egg

Humans 22 pairs of autosomes 1 pair of sex chromosmes Males = XY Females = XX

Human Reproductive cells XX x XY XX XXX YXY

Pedigree Pedigree – diagram that shows the inheritance pattern of a single gene through several generations in a family

Blood Groups Human blood groups – controlled by multiple alleles = 3 or more alleles of the same gene Blood group alleles = ABO

Blood Groups Karl Landsteiner – 1900 discovered human blood groups Agglutinated blood – clumping of blood due to mixing of different types

A & B antigens – presence or absence of these determine blood type GenotypesPhenotypes iiType O I A I A, I A iType A I B I B, I B iType B IAIBIAIB Type AB

Blood Types GenotypephenotypeUS population AA or AOBlood type A41% BB or BOBlood type B10% ABBlood type AB4% OOBlood type O45%

Blood Genotypes A and B antigens – presence or absence of antigens determine blood types; recognized by immune system A and B are codominant

Rh blood groups – named after Rhesus monkey Rh antigen present = Rh + Rh antigen present = Rh –

Blood Groups Rh factor – proteins on surface of RBC Rh + Rh -

Huntington’s Disease Produced by a single dominant allele (H) No symptoms until approx age 40 Starts as gradual damage to nervous system

Huntington’s Disease Leads to painful progressive loss of muscle control and mental function Parent with HD -  children have a 50% of developing disease

Huntington’s Disease In 1872, George Huntington 1 st documented Huntington’s disease. He called it Huntington’s chorea. (Chorea = dance in Greek) People with this disorder often had involuntary, erratic movements suggestive of a dance. After 1963, the disorder became known as Huntington’s disease

Huntington’s Disease The dominant allele that causes Huntington’s disease was brought to the United States in 1630 by three men whose families had been persecuted for witchcraft in England because of their strange behavior and mental disturbances. At the time, these symptoms were believed to be caused by consorting with the devil.

Sickle Cell Anemia Anemia – shortage of RBC’s James Herrick – 1904 – discovered disease Symptoms – weakness, dizziness, pain, open sores RBC’s are sickle shaped

Sickle Cell Anemia Caused by a change in one of the polypeptides found in hemoglobin Hemoglobin – carries O 2 in the blood Sickle RBC’s – become rigid and break easily; can become lodged in capillaries; can cause tissue damage

Sickle Cell Anemia A = normal hemoglobin S = sickle cell gene A and S are co- dominant

Human Genetic Disorders Sickle Cell Anemia Blood disorder Crescent shaped RBC Recessive allele RBC gets stuck in small blood vessels

Sickle Cell AA – normal AS – heterozygous; sickle cell carriers; ½ blood normal; ½ blood sickle shaped SS – sickle cell ; severely affected

Polygenic Traits Polygenic traits – traits controlled by many genes Examples – height, weight, skin color, intelligence, hair color Poly = many

Polygenic Traits Polygenic traits – traits determined by many genes Examples – skin color, height, eye color, intelligence

Cystic Fibrosis Cystic fibrosis – most common genetic disorder in N.A. 1 in 28 Americans carry recessive allele Caused by a defective protein in plasma membrane

Cystic Fibrosis Results in the accumulation of thick mucus in lungs and digestive tract

Nondisjunction Nondisjunction – failure of chromosomes to separate properly during meiosis Nondisjunction disorders – occur in 1 birth in 1000

Nondisjunction disorders Turners syndrome – 45XO or 45 X; female in appearance; missing one sex chromosome Klinefelters syndrome – 47 XXY; male in appearance; usually sterile

Nondisjunction disorders X chromosome – essential for survival Y chromosome – determines sex; during birth codes for the production of testosterone 48 XXXY and 49 XXXXY are male

Nondisjunction disorders Trisomy 21 = Downs syndrome – nondisjunction of autosomes during meiosis, extra copy of 21 st chromosome; results in metal retardation 1 in 800 babies born with Downs

Sex-linked Inheritance Sex-linked – genes located on sex chromosomes Y chromosome – carries few genes Females = XX Males = XY

Sex-Linked Inheritance Sex-linked traits more common expressed in males; they only need 1 copy of the recessive allele

Sex-linked Disorders Colorblindness – recessive, sex-linked disorder Gene for colorblindness – people unable to make some of the pigments necessary for color vision

Colorblindness X C X C – normal vision female X C X c – carrier female X c X c – colorblind female X C Y – normal male X c Y – colorblind male

Colorblindness Color vision –Cone cells of retina allow organisms to see color –Rod cells – allow organisms to see shades of light and dark

Sex-linked traits Hemophilia - recessive sex-linked disorder Protein necessary for blood clotting is missing Causes internal hemorrhaging for slightest bruise or cut

Royal Hemophilia

Hemophilia genotypes Female genotypes X H X H – normal X H X h – carrier X h X h - hemophilia Male Genotypes X H Y – normal X h Y - hemophilia

Hemophilia

Sex-Linked Traits Duchenne Muscular Dystrophy – caused by gene on X chromosome Symptoms – weakening of skeletal muscles Only affects males Death in early 20’s

Duchenne MD Genotypes Female genotypes X D X D – normal X D X d – carrier X d X d - MD Male genotypes X D Y – normal X d Y - MD

Duchenne Muscular Dystrophy In US affects 1 out of 3000 males Causes weakening of muscles Sex-linked; more common in males

Sex-Influenced Traits Trait that is caused by a gene whose expression differs in males and females Male pattern baldness – sex influence

Male pattern baldness GenotypeMaleFemale BBNormal hair BbBaldnessNormal hair bbBaldnessVery thin hair

Prenatal Diagnosis Amniocentesis – small amount of fluid surrounding the embryo sac is removed Can detect genetic disorders

Prenatal Diagnosis Chorionic villus sampling – sample of embryonic cells is removed from membrane surrounding embryo