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Chapter 12

Chapter 12. Chromosomes and Human Inheritance. Human Chromosomes. Diploid = 46, Haploid = 23 Sex chromosomes different than others Not homologous pairs Female = two X chromosomes (XX) Male = one X & one Y chromosome (XY) Autosomes —non-sex chromosomes, same in both genders. karyotyping.

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Chapter 12

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  1. Chapter 12 Chromosomes and Human Inheritance

  2. Human Chromosomes • Diploid = 46, Haploid = 23 • Sex chromosomes different than others • Not homologous pairs • Female = two X chromosomes (XX) • Male = one X & one Y chromosome (XY) • Autosomes—non-sex chromosomes, same in both genders

  3. karyotyping • Culture cells, stimulate mitosis, stop division at metaphase • Hypotonic solution swells cells, separates them & chromosomes • Take picture, cut & paste

  4. Autosomal inheritance • Autosomal Dominant • Allele expressed in heterozygotes • AA or Aa show dominant phenotype

  5. Autosomal dominant • Achondroplasia • Embryonic cartilage in skeleton doesn’t develop properly • “Dwarf”, average 4’ tall • Huntington’s Disease • Nervous system deteriorates • Symptoms often not seen until after 30 • Die in 40s or 50s

  6. Autosomal inheritance • Autosomal Recessive • Recessive phenotype only shown with homozygous recessive • Heterozygous is “carrier”

  7. Autosomal recessive • Albinism • Lack of normal amounts of melanin (pigment) in body • Cystic fibrosis • Thick mucus in lungs & digestive tract • Breathing & digestion difficult • Most common lethal genetic disorder among caucasians

  8. Sex determination • Humans • XX = Female • XY = Male

  9. Sex determination • Fetal development • 7 weeks, “uncommitted” • Y chromosome present  male sex organs • Y chromosome absent  female sex organs

  10. Sex determination • Different species have different systems • X-Y • XX = Female, XY = Male • X-O • XX = Female, X = Male • Z-W • ZW = Female, ZZ = Male • Haplo-Diploid • 2n = Female, n = Male

  11. X-Linked inheritance • Non-sexual gene “linked” to a sex chromosome (X) • NOT present on Y chromosome • Recessive & dominant alleles • XR, Xr, Y • XRXR, XRXr, XRY = dominant phenotype • XrXr, XrY = recessive phenotype

  12. X-linked inheritance XB = Bald, recessive trait X, Y = Non-bald, dominant trait XB Y XB Y X X XB X X Y XBXB= bald woman XXB = carrier woman XX = normal woman XBY = bald man XY = normal man XB X

  13. X-Linked inheritance • Baldness • Red-Green Color Blindness • Hemophilia A • Lack of certain clotting factors • Blood cannot clot, bleed uncontrollably

  14. Chromosome structure • Changes in physical structure of chromosome • Cause genetic disorders or abnormalities • Rare • Duplication • Deletion • Inversion • Translocation

  15. duplication • DNA sequences are repeated 2 or more times • Unequal crossing-over • Broken piece of chromosome attaches to homologous chromosome • Huntington’s Disease • Affects coordination & movement • Affects mental abilities, personality

  16. deletion • DNA sequence deleted • Unequal crossing-over • Chemical damage • Most cause serious disorders or death • Cri du chat syndrome • Severe developmental & neurological problems • Unusual cry of infant (“cry of the cat”) • Unusual physical appearance

  17. inversion • DNA sequence reverses • No loss of DNA or chromosome part • No problem for carrier if non-crucial gene • Some may not know until children have problem • Chromosome 9 • No health problems for parent • May increase risk of miscarriage

  18. translocation • Broken part of one chromosome attaches to another • Usually reciprocal (both exchange broken parts) • Often cause reduced fertility • Severe problems rare • Can include several cancers

  19. Chromosome number • Aneuploidy—one more one less chromosome than normal • Usually fatal for humans • Most miscarriages • Nondisjunction—one or more pairs do not separate during meiosis • Polyploidy—cells with 3 or more copies of one or more chromosomes • Trisomic—cells with 2n+1 of one chromosome, 2n of all others

  20. nondisjunction

  21. Down syndrome • Only trisomy that reaches adulthood • Extra copy of chromosome 21 • Mostly through nondisjunction at meiosis • Abonormal mental, heart, and skeletal development

  22. Sex chromosome abnormalities • Turner syndrome • Nondisjunction of sex chromosomes • Only one X, noted as “XO” • 98% of embryos miscarry • Adults very short, but well proportioned • Sterile, limited sex hormones • Klinefelter syndrome • 2/3 Nondisjunction of sex chromosomes • XXY • Mostly normal, some learning disabilities • Lower testosterone, higher estrogen • “Feminized” male characteristics

  23. Human genetic developments • Phenotype treatments • Phenylketonuria (PKU)—lack of enzyme, can’t convert certain amino acid, brain function problems • Restrict intake, can lead normal life • Genetic screening • Detect alleles that can cause disorders • Prenatal diagnosis • Amniocentesis—collect fluid from around fetus • Cells in fluid from fetus, can analyze for disorders

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