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Chapter 12 Section 3-Complex Inheritance of Human Traits

Chapter 12 Section 3-Complex Inheritance of Human Traits. I) Codominance in Humans. **Note: phenotypes of both homozygotes are produced in heterozygotes  ex/sickle cell anemia B) Sickle Cell Anemia (SCA) i) Basics of SCA Major health problems in US & Africa

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Chapter 12 Section 3-Complex Inheritance of Human Traits

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  1. Chapter 12Section 3-Complex Inheritance of Human Traits

  2. I) Codominance in Humans • **Note: phenotypes of both homozygotes are produced in heterozygotes  ex/sickle cell anemia B) Sickle Cell Anemia (SCA) i) Basics of SCA • Major health problems in US & Africa • Most common among in black Americans w/ origins in Africa & white Americans with origins in the countries that surround the Med. Sea • 1/12 African American is heterozygote for SCA

  3. I) Codominance in Humans • Basics of SCA • Hemoglobin is a protein that carries O2 in red blood cells (RBC) • Individuals who are homozygotes for SCA have defective hemoglobins which form crystal-like structures that cause shape changes in RBC Sickle Cell RBC Half-moon or sickle shaped Normal RBC Disc Shaped

  4. I) Codominance in Humans ii)How sickle cell works? • Gene for hemoglobin produces protein that differs from normal hemoglobin by 1 AA • SCA hemoglobin crystallizes when O­2 levels are low after hemoglobin delivers O2 to cells in narrow capillaries • Causes change in RBC from disc shaped  sickle shape (see Fig.12.16) • Sickle shaped RBC slow blood flow and block small vessels • Can result in: • Pain • Tissue damage • Short life span of RBC

  5. I) Codominance in Humans iv) Codominance of SCA • Individuals who are heterozygotes for SCA means that they produce both: • normal hemoglobin • SCA hemoglobin (ex/ of codominance) and they have the SCA trait • These individuals produce enough normal hemoglobins to prevent serious health problems and can live relatively normal lives • These individuals can show signs of SCA related to disorders if O2 availability reduced

  6. II) Multiple Alleles govern blood type • ABO blood type grp classic example of single gene with multiple alleles in humans i) Human Blood Types • Human blood types determined by presence or absence of certain molecules on surface of RBC • Blood Type Gene: I • (3) alleles that can be present on I gene: • IA= surface molecule A • IB= surface molecule B • i = no surface molecule

  7. GENOTYPES Type A:_____ Type B:____ Type AB:_______ Type O:___ Possibilities Type A:_____ Type B:_____

  8. II) Multiple Alleles govern blood type B) Importance of Blood typing (B.T.) • Blood typing important b/c: • Incompatible blood type given through blood transfusion can cause other blood types to clump causing death • Can be used to solve parentage: • Ex/ Child has blood type AB, Mother has blood type A, what must the father’s blood type be?

  9. II) Sex-linked traits in Humans • Many human traits are determined by genes carried on sex chromosomes • Most genes carried on the X chromosome A) How sex chromosomes are passed on? • Males Females X X Y X Can be passed to either sons or daughters Passed on to Daughters only Passed on to Sons only

  10. II) Sex-linked traits in Humans • If son receives allele on X chromosomes it will be expressed b/c males have only 1 chromosome • 2 traits that are X-linked disorders are: • Red-green blindness • Hemophilia B) Red-green colorblindness • Individual can’t distinguish between red & green • Caused by recessive allele found at 1 of (2) gene sites on X chromosome • Both genes affect red & green receptors in eye cells • Can cause problems w/ driving  traffic lights

  11. Color Blindness Tests

  12. II) Sex-linked traits in Humans C) Hemophilia: An X-linked Disorder • Clotting ability necessary human adaptation • If clotting ability not present, could result in: • Excess blood loss due to minor injury • Serious blood loss due to internal injury • Major blood loss due to bruising • Hemophilia A • X-linked disorder causing a blood clotting problem • 1/10,000 males have hemophilia • 1/100 million female have hemophilia

  13. II) Sex-linked traits in Humans C) Hemophilia: An X-linked Trait • Hemophilia A • Males receive hemophilia allele from carrier mothers on X chromosome • 1 recessive allele = hemophilia in males • 2 recessive alleles = hemophilia in females • Treatment of hemophilia: • Blood transfusions • Injections of Factor VIII (this is a blood clotting enzyme that is absent in hemophilic patients

  14. III) Polygenic Inheritance in Humans • Many human traits are determined by polygenic inheritance • Ex/ variations in eye color (humans) • Ex/variations in skin color (humans) i) Skin Color: A polygenic trait • 1900s-skin color data used to test polygenic inheritance theory • Light skinned individual x Dark Skinned individual • Intermediate skin color

  15. III) Polygenic Inheritance in Humans • F2 generation: • results in range of skin colors from light skinned dark skinned like P1 generation w/ most having intermediate skin color • Variation led to skin color being polygenic & has 3-4 genes involved

  16. Remember abnormal chromosomes # usually happens b/c of meiosis accidents (Process Called _________________) Human chromosome: Pairs of chromosomes = 23 Total chromosomes = 46 A) Abnormal numbers of Autosomes Trisomic Humans-those individuals who have either partial/whole extra chromosome Trisomy usually caused by nondisjunction III) Changes in Chromosome Numbers

  17. III) Changes in Chromosome Numbers i) How abnormal chromosomes are ID’ed? • Sample of cells obtained from fetus or individual • Metaphase chromosomes photographed & images are enlarged & arranged by length & location of Centromere • Chart of chromosomes is called a karyotype • Karyotype-def-pg329-chart of metaphase chromosome pairs arranged according to length & location of the Centromere; used to pinpoint unusual chromosome #s in cells • Karyotypes valuable in ID’ing unusual chromosome #s in cells

  18. III) Changes in Chromosome Numbers B) Down Syndrome: Trisomy 21 • Most embryo w/abnormal chromosome # result in death of the embryo • Down syndrome only autosomal trisomy that results in embryo surviving to birth and adulthood. • Down syndrome happens in 1/700 live births ii) Symptoms of Down Syndrome: • Some degree of mental retardation • Short stature • Weak muscles through out body • Short, wide neck with excess skin • Short/stocky arms & legs • Facial features: sm. Low set ears/nasal bridge pushed in/ irregular mouth & tongue • Incident of Down Syndrome births is er in older mothers (especially over 40)

  19. III) Changes in Chromosome Numbers C) Abnormal numbers of sex chromosomes • Many abnormalities in # of sex chromosomes • Any individuals w/ at least one Y chromosome is male • Most individuals w/abnormal # of sex chromosomes lead normal lives, but some may result in: • Klinefelter syndrome (XXY)-sm testes, usually sterile • XYY-may be taller than normal • Turner’s syndrome (XO)- monosomy X-have sex organs which don’t mature/women sterile/short/heart defects common

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