1 Chapter 11 Complex Inheritance and Human Heredity 11.3 Chromosomes and Human Heredity.

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  • Chapter 11 Complex Inheritance and Human Heredity11.3 Chromosomes and Human Heredity

  • Karyotype StudiesKaryotype is a micrograph (picture) of chromosomes at metaphase arranged by size in homologous pairs. Twenty-two pairs of autosomes are the same for males and females.Males have one X chromosome and one Y chromosome (not paired) and females have two X chromosomes (paired).Karyotypes are useful for detecting chromosome abnormalities

  • Karyotype StudiesChromosome smearKaryotype

  • TelomeresTelomeres protective end caps on the chromosomes made of DNA and proteins.Short repetitive nonessential DNA sequencesPrevent one chromosome form binding to another chromosome (not sticky)

  • TelomeresAbsolutely essential for chromosome functionTelomeres decrease in size (length) as an organism ages and may play a role in aging and cancer.Cancer cells have increased length of telomeres compared to adult cells.Telomere function is an intense field of research

  • NondisjunctionFailure of chromosomes to separate during cell divisionResults in one cell getting too many chromosomes and one cell not getting enough.If nondisjunction occurs during meiosis the resulting gametes could form an organism with every cell having an incorrect chromosome number.

  • Down SyndromeResults of parental gamete nondisjunction resulting in trisomy (three chromosomes ) of chromosome #21.Symptoms include: mental retardation, distinctive facial features, short stature, heart defects, sexually underdeveloped, sterile, more likely to develop leukemia and Alzheimer's, shorter life span

  • Down Syndrome

  • Down SyndromeIncidence of Down Syndrome increases with increasing age of the motherRisk increases to 6% for mothers over age 45Recommended fetal testing for mothers age 35 and older

  • Other TrisomysPatau syndrome: trisomy 13; 1/5000; serious eye, brain and circulatory problems; lifespan less than 1 yearEdwards syndrome: trisomy 18; 1/10,000; effects every body organ; lifespan less than 1 year

  • Nondisjunction of Sex Chromosomes MaleKlinefelter syndrome: (XXY); 1/2000; males sex organs, testes abnormally small; sterile; feminine body characteristics (breast enlargement, fat deposition); normal intelligence(XYY); taller than average male; not characterized by a syndrome; some suggest increased aggression

  • Nondisjunction of Sex Chromosomes Female(XXX): 1/1000; normal due to X inactivitation; only distinguishable by karyotypeTurner syndrome Monosomy X (XO): 1/5000; female with no maturation of sex organs; no secondary sex characteristics; short; sterile; normal intelligence with spatial learning disabilities

  • Fetal TestingAmniocentesis: removal amniotic fluid with sloughed fetal cells at 14th -16th week; for diagnosis of chromosomal abnormalities; 1% risk of complications

  • Fetal TestingChorionic villus sampling: removal of placental sample at 8th -10th week; quicker results; less accurate; less than 1% risk of complications

  • Fetal TestingFetal blood sampling: sample of fetal blood; can detect increased number of genetic abnormalities; medication can be given to fetus before birth; greater risk to fetus

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