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Chapter 11 Complex Chapter 11 Complex Inheritance and Human Inheritance and Human

HeredityHeredity

11.3 Chromosomes and 11.3 Chromosomes and Human HeredityHuman Heredity

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Karyotype StudiesKaryotype Studies

Karyotype is a micrograph (picture) of Karyotype is a micrograph (picture) of chromosomes at metaphase arranged by chromosomes at metaphase arranged by size in homologous pairs. size in homologous pairs.

Twenty-two pairs of autosomes are the Twenty-two pairs of autosomes are the same for males and females.same for males and females.

Males have one X chromosome and one Y Males have one X chromosome and one Y chromosome (not paired) and females chromosome (not paired) and females have two X chromosomes (paired).have two X chromosomes (paired).

Karyotypes are useful for detecting Karyotypes are useful for detecting chromosome abnormalitieschromosome abnormalities

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Karyotype StudiesKaryotype Studies

Chromosome smear

Karyotype

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TelomeresTelomeres

Telomeres protective Telomeres protective end caps on the end caps on the chromosomes made of chromosomes made of DNA and proteins.DNA and proteins.

Short repetitive Short repetitive nonessential DNA nonessential DNA sequencessequences

Prevent one Prevent one chromosome form chromosome form binding to another binding to another chromosome (not chromosome (not sticky)sticky)

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TelomeresTelomeres Absolutely essential for Absolutely essential for

chromosome functionchromosome function Telomeres decrease in Telomeres decrease in

size (length) as an size (length) as an organism ages and organism ages and may play a role in may play a role in aging and cancer.aging and cancer.

Cancer cells have Cancer cells have increased length of increased length of telomeres compared to telomeres compared to adult cells.adult cells.

Telomere function is Telomere function is an intense field of an intense field of researchresearch

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NondisjunctionNondisjunction

Failure of chromosomes to separate Failure of chromosomes to separate during cell divisionduring cell division

Results in one cell getting too many Results in one cell getting too many chromosomes and one cell not getting chromosomes and one cell not getting enough.enough.

If nondisjunction occurs during If nondisjunction occurs during meiosis the resulting gametes could meiosis the resulting gametes could form an organism with every cell form an organism with every cell having an incorrect chromosome having an incorrect chromosome number.number.

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Down SyndromeDown Syndrome

Results of parental gamete Results of parental gamete nondisjunction resulting in trisomy (three nondisjunction resulting in trisomy (three chromosomes ) of chromosome #21.chromosomes ) of chromosome #21.

Symptoms include: mental retardation, Symptoms include: mental retardation, distinctive facial features, short stature, distinctive facial features, short stature, heart defects, sexually underdeveloped, heart defects, sexually underdeveloped, sterile, more likely to develop leukemia sterile, more likely to develop leukemia and Alzheimer's, shorter life spanand Alzheimer's, shorter life span

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Down SyndromeDown Syndrome

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Down SyndromeDown Syndrome Incidence of Down Incidence of Down

Syndrome increases Syndrome increases with increasing age with increasing age of the motherof the mother

Risk increases to Risk increases to 6% for mothers over 6% for mothers over age 45age 45

Recommended fetal Recommended fetal testing for mother’s testing for mother’s age 35 and olderage 35 and older

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Other TrisomysOther Trisomys

Patau syndrome: trisomy 13; 1/5000; Patau syndrome: trisomy 13; 1/5000; serious eye, brain and circulatory serious eye, brain and circulatory problems; lifespan less than 1 yearproblems; lifespan less than 1 year

Edward’s syndrome: trisomy 18; Edward’s syndrome: trisomy 18; 1/10,000; effects every body organ; 1/10,000; effects every body organ; lifespan less than 1 yearlifespan less than 1 year

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Nondisjunction of Sex Nondisjunction of Sex Chromosomes MaleChromosomes Male

Klinefelter syndrome: (XXY); 1/2000; Klinefelter syndrome: (XXY); 1/2000; males sex organs, testes abnormally males sex organs, testes abnormally small; sterile; feminine body small; sterile; feminine body characteristics (breast enlargement, characteristics (breast enlargement, fat deposition); normal intelligencefat deposition); normal intelligence

(XYY); taller than average male; not (XYY); taller than average male; not characterized by a “syndrome”; characterized by a “syndrome”; some suggest increased aggressionsome suggest increased aggression

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Nondisjunction of Sex Nondisjunction of Sex Chromosomes FemaleChromosomes Female

(XXX): 1/1000; normal due to X (XXX): 1/1000; normal due to X inactivitation; only distinguishable by inactivitation; only distinguishable by karyotypekaryotype

Turner syndrome Monosomy X (XO): Turner syndrome Monosomy X (XO): 1/5000; female with no maturation of 1/5000; female with no maturation of sex organs; no secondary sex sex organs; no secondary sex characteristics; short; sterile; normal characteristics; short; sterile; normal intelligence with spatial learning intelligence with spatial learning disabilitiesdisabilities

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Fetal TestingFetal Testing

AmniocentesisAmniocentesis: : removal amniotic removal amniotic fluid with sloughed fluid with sloughed fetal cells at 14fetal cells at 14thth - -1616thth week; for week; for diagnosis of diagnosis of chromosomal chromosomal abnormalities; 1% abnormalities; 1% risk of risk of complicationscomplications

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Fetal TestingFetal Testing

Chorionic villus Chorionic villus samplingsampling: removal : removal of placental sample of placental sample at 8at 8thth -10 -10thth week; week; quicker results; quicker results; less accurate; less less accurate; less than 1% risk of than 1% risk of complicationscomplications

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Fetal TestingFetal Testing

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