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Division Ave High School Ms. FogliaAP Biology
AP Biology 2006-2007
Chromosomal Inheritance
AP Biology
Chromosomal Theory of Inheritance§ Formulated by Sutton in 1902§ Showed that chromosomes play a key
role in inheritance.
AP Biology
Sex Linkage§ Morgan in 1902 studied fruit flies§ Discovered that only males showed the
mutant white eye color (normal is red)§ Showed that eye color was on the sex
(X) chromosome. Females (XX) males (XY)
§ Genes on the X chromosome are sex-linked because recessive traits show different inheritance in males and females
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Division Ave High School Ms. FogliaAP Biology
AP Biology
Dosage compensation§ Males on get one copy of genes on the
X chromosome§ Females do not make 2x as much
protein and the malesu Instead one of the X-chromosomes is
inactivated in each cell§ X-Chromosomes are inactivated by
becoming highly condensed into Barr bodiesw Can create genetic mosaics
-ie calico cats
AP Biology
Chromosomal abnormalities§ Incorrect number of chromosomes
u nondisjunction§ chromosomes don’t separate properly
during meiosis u breakage of chromosomes
§ deletion§ duplication§ inversion§ translocation
AP Biology
Nondisjunction § Problems with meiotic spindle cause errors in
daughter cellsu homologous chromosomes do not separate
properly during Meiosis 1u sister chromatids fail to separate during Meiosis 2u too many or too few chromosomes
2n n
n
n-1
n+1
3
Division Ave High School Ms. FogliaAP Biology
AP Biology
Alteration of chromosome number
all with incorrect number 1/2 with incorrect number
error in Meiosis 1
error in Meiosis 2
AP Biologytrisomy
2n+1
Nondisjunction § Baby has wrong chromosome number
u trisomy§ cells have 3 copies of a chromosome
u monosomy§ cells have only 1 copy of a chromosome
n+1 n
monosomy2n-1
n-1 n
AP Biology
Human chromosome disorders § High frequency in humans
u most embryos are spontaneously abortedu alterations are too disastrousu developmental problems result from biochemical
imbalance§ imbalance in regulatory molecules?
w hormones?w transcription factors?
§ Certain conditions are toleratedu upset the balance less = survivableu but characteristic set of symptoms = syndrome
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Division Ave High School Ms. FogliaAP Biology
AP Biology
Down syndrome§ Trisomy 21
u 3 copies of chromosome 21u 1 in 700 children born in U.S.
§ Chromosome 21 is the smallest human chromosomeu but still severe effects
§ Frequency of Down syndrome correlates with the age of the mother
AP Biology
Down syndrome & age of motherMother’s age
Incidence of Down Syndrome
Under 30 <1 in 100030 1 in 90035 1 in 40036 1 in 30037 1 in 23038 1 in 18039 1 in 13540 1 in 10542 1 in 6044 1 in 3546 1 in 2048 1 in 1649 1 in 12
Rate of miscarriage due to amniocentesis:§ 1970s data
0.5%, or 1 in 200 pregnancies
§ 2006 data<0.1%, or 1 in 1600 pregnancies
AP Biology
Genetic testing§ Amniocentesis in 2nd trimester
u sample of embryo cellsu stain & photograph chromosomes
§ Analysis of karyotype
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Division Ave High School Ms. FogliaAP Biology
AP Biology
Sex chromosomes abnormalities§ Human development more tolerant of
wrong numbers in sex chromosome§ But produces a variety of distinct
syndromes in humansu XXY = Klinefelter’s syndrome male u XXX = Trisomy X femaleu XYY = Jacob’s syndrome maleu XO = Turner syndrome female
AP Biology
§ XXY maleu one in every 2000 live birthsu have male sex organs, but
are sterileu feminine characteristics
§ some breast development§ lack of facial hair
u tallu normal intelligence
Klinefelter’s syndrome
AP Biology
Klinefelter’s syndrome
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Division Ave High School Ms. FogliaAP Biology
AP Biology
Jacob’s syndrome male§ XYY Males
u 1 in 1000 live male births
u extra Y chromosomeu slightly taller than
averageu more activeu normal intelligence, slight learning disabilitiesu delayed emotional maturityu normal sexual development
AP Biology
Trisomy X§ XXX
u 1 in every 2000 live birthsu produces healthy females
§ Why?§ Barr bodies
w all but one X chromosome is inactivated
AP Biology
Turner syndrome§ M�onosomy X or X0
u 1 in every 5000 birthsu varied degree of effects u webbed necku short statureu sterile
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Division Ave High School Ms. FogliaAP Biology
AP Biology
Changes in chromosome structure§ deletion
u loss of a chromosomal segment§ duplication
u repeat a segment§ inversion
u reverses a segment§ translocation
u move segment from one chromosome to another
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AP Biology 2006-2007
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