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Chapter 12

Chapter 12. Patterns of Inheritance. Gene and Allele. Gene - sequence of DNA found in a specific site (locus) on a chromosome. Determines a trait or characteristic in a human. Allele - alternate forms of a gene that occupy the same loci on a chromosome.

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Chapter 12

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  1. Chapter 12 Patterns of Inheritance Created by C. Ippolito April 2006

  2. Gene and Allele • Gene - sequence of DNA found in a specific site (locus) on a chromosome. • Determines a trait or characteristic in a human. • Allele - alternate forms of a gene that occupy the same loci on a chromosome. • The interaction of 2 alleles on a chromosome pair determine a person’s trait. Created by C. Ippolito April 2006 2

  3. Sex Determination • Sex of a child is determined by the male parent. • Sex cells of parents contain one member of each pair. • The egg will always have an Xsperm can have an X or Y. • Female - egg is fertilized by a sperm bearing an X chromosome. • Male - egg is fertilized by a sperm bearing an Y chromosome. Created by C. Ippolito April 2006 3

  4. Mendel’s Laws • GregorMendel • Austrian monk • first to explain how characteristics are passed • Experimented with pea plants Created by C. Ippolito April 2006

  5. Law of Segregation • Each trait is determined by twofactors. • In sex cells factorsseparate. • Zygote gets one factor from each parent. Created by C. Ippolito April 2006

  6. Law of Dominance • Mendel determined that certain factors overpowered the appearance of others. • Dominant – overpowers • presence of factor forcestrait to appear regardless of the form of the other factor on its companion chromosome. • Recessive - is overpowered • Both chromosomes must possess this factor for trait to appear Created by C. Ippolito April 2006

  7. Genotype • the actualgenepairs or alleles present to cause a trait. • There are two genotypes: • Homozygous • Genotype with twoidenticalalleles causing a trait. • TT - homozygous dominant • tt - homozygous recessive - the onlyway a recessive can show • Heterozygous • Genotype with twodifferentalleles causing a trait. • Tt - only dominant appears Created by C. Ippolito April 2006

  8. Phenotype • the physicalappearance caused by the alleles. • Both TT and Tt have sameappearance - tallness Created by C. Ippolito April 2006

  9. Law of Independent Assortment • Factor inherited in one gene does not affect the factor that will be inherited in another gene • not true if genes are linked - found on same chromosome Created by C. Ippolito April 2006

  10. Polygenic (Multifactorial ) Inheritance • Single trait controlled by two or more sets of alleles. • Traits show continuous variation “bell curve” • The greater the number of alleles the more perfect the bell curve will be. • Known polygenic traits: • Skin Color • Height • Possible polygenic traits • Cleft Palate • Club Foot • Hypertension • Diabetes • Schizophrenia • Allergies Created by C. Ippolito April 2006 10

  11. Multiple Alleles • Trait controlled one gene pair with more than two distinct alleles. • Human Blood types • IA - codominant -causes A blood • IB - codominant -causes B blood • i - recessive -cause O blood • Incomplete Dominance • Alleles for A and B do not dominate so the heterozygote IAIB has what is known as Type AB blood Created by C. Ippolito April 2006 11

  12. Type A IAi - heterozygous for A IAIA - homozygous for A produces anti-B can be given A or O blood Type B IBi - heterozygous for B IBIB- homozygous for B produces anti-A can be given B or O blood Type AB IAIB - heterozygous for AB produces no antibody Universal Receiver can be given any blood Type O ii - homozygous for O produces anti-A and anti-B Universal Donor can be given only O blood Blood Types • Protein marker (antigen) on membrane of the RBC. Created by C. Ippolito April 2006 12

  13. Pleiotropy • One gene affects many traits. • Sickle Cell Anemia • Recessive - mainly affects African Americans • abnormal hemoglobin • Mutation substituted a valine for glutamic acid • originated in areas where malaria was endemic • HbN = normal Hbn = sickle • HbNHbN - normal but can get malaria • HbNHbn - normal but immune to malaria • HbnHbn - sickle cell anemia Created by C. Ippolito April 2006 13

  14. Gene Linkage • Linked Traits • Inherited together because on same chromosome pair • Exception Law of Independent Assortment Created by C. Ippolito April 2006 14

  15. Crossing Over • During synapsis of meiosis chromosomes exchange pieces • Breaks linkage Created by C. Ippolito April 2006 15

  16. Sex-Linked Genes • genes on the “X” with no equivalent part on the “Y” • appear more often in males - inherit only one allele • hemophilia • Duchenne Muscular Dystrophy • colorblindness Created by C. Ippolito April 2006

  17. Chromosome Abnormalities • chromosome pairs do not separate properly • Nondisjunction is the failure of chromosome pairs to separateproperly. Created by C. Ippolito April 2006

  18. Nondisjunction • The failure to separate results in: • sex cells extrachromosome • or • sex cells missingchromosome Created by C. Ippolito April 2006

  19. Down Syndrome • Trisomy21 • 1:800 < 40 ♀ 1:90 > 40 ♀ • short stature; enlarged tongue • rounded head; eyefold • mentalretardation Created by C. Ippolito April 2006

  20. Down Syndrome Karyotype Created by C. Ippolito April 2006

  21. Cri du Chat Syndrome • Monosomy5 (piece deleted) • moon face as infant • malformed larynx • eyefold • misshapen, low ears • severementalretardation Created by C. Ippolito April 2006

  22. Fragile X Syndrome • 1:1000 ♂ 1:2500♀ • children • normal but hyperactive or autistic • adults: • short stature; long face • prominent jaw; large ears • stubby hands • ♂’s more likely to be mentally deficient Created by C. Ippolito April 2006

  23. Turner Syndrome • 45, XO 1:6000 ♀ • short with broad chest • webbed neck • ovaries, oviduct, uterus small • nopuberty; nomenstruation • most normal mentally Created by C. Ippolito April 2006

  24. Turner Syndrome Karyotype Created by C. Ippolito April 2006

  25. Klinefelter Syndrome • 47, XXY 1:1500 ♂ • genitalia, testes, prostate small • no 2o sex characteristics • some breast development • large hands, feet; long limbs • slow but no deficiency (XXXY) Created by C. Ippolito April 2006

  26. Klinefelter Karyotype Created by C. Ippolito April 2006

  27. Jacob Syndrome • 47, XYY 1:1000 ♂ • taller than normal • persistent acne • speech & reading problems • more aggressive due to size • “criminal” syndrome Created by C. Ippolito April 2006

  28. Human Genetic Disorders Created by C. Ippolito April 2006

  29. Achondroplasia • Autosomal dominant allele • Gene controlling fibroblast function • short stature, legs and arms short compared to trunk (body), prominent forehead, a protruding jaw, bowed legs • Diagnosis • X-ray and clinical interview • Molecular testing can identify mutated gene (FGFR3) • Treatment • monitor growth, check for apnea, surgical correction if walking difficult • Genetic Counseling Created by C. Ippolito April 2006

  30. Huntington’s Chorea • Autosomal dominant allele • 1:20,000 births • Chronic neurological disease • slow destruction of brain cells. • uncontrolled motions • appears in middle age (40’s) • death within 10 to 20 years of onset • Woody Guthrie - hobo poet and folk singer - “This Land is Your Land” • No Cure; No treatment • Gene has been identified and presence can be determined by blood test Created by C. Ippolito April 2006 30

  31. Albinism • Autosomal recessive allele • Missing pigments • in skin, hair, and eyes • low vision due to abnormal retina • Treatment • sunscreen protection and opaque clothing • vision aids • Type I • missing enzyme to form pigment • Type II • some pigment formed “P” gene defective Created by C. Ippolito April 2006

  32. Cystic Fibrosis • Autosomal recessive allele • 1:20 Caucasians are carriers • occurs in 1:2,500 births • bronchial mucus becomes very thick and viscous • Mucus sits in alveoli and bronchi • Daily manual message known as “cupping and clapping” used to loosen mucus. • Regular visits to hospital needed to “suction” lungs • usually die before their 18th birthday • current treatment may extend life into 28 • No cure but gene has been identified • Genetic screening possible Created by C. Ippolito April 2006 32

  33. Phenylketonuria (PKU) • Autosomal recessive • 1:5,000 • No enzyme – to break down phenylalanine. • phenylketone build up which can harm developing brain cells. • mental retardation. • Diagnosis - blood test at birth. • Treatment • special diet low in phenylalanine until age 7. • Adults • excess phenylalanine causes headaches Created by C. Ippolito April 2006 33

  34. Tay Sachs Disease • Autosomal recessive • high occurrence in American Jews - 1:1,000 births • higher occurrence in Ashkenazy Jews - 1:40 births • Lipid buildup around nerve cells. • Normal until 4 months of age. • 5th month - lethargy • 8th month reactions and movements not normal • child becomes blind, deaf, has seizures, paralysis, and dies before 5th year. • No cure, no treatment, no definite test for presence of gene • Genetic Counseling - Carriers should not marry Created by C. Ippolito April 2006 34

  35. Human Traits • Pedigree Chart • a diagram that shows the relationships within a family • a circle represents a female • a square represents a male • horizontal line connecting a circle to a square represents a marriage • a filled-in circle or square shows that the individual has the trait • vertical line(s) and brackets below that line show their child(ren) Created by C. Ippolito April 2006

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