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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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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

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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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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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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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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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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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division ave high school ms. foglia ap biology · 1 division ave high school ms. foglia ap biology...

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