5. ch15 chromosomal abnormalities.ppt

8/14/2019 5. Ch15 Chromosomal Abnormalities.ppt

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AP Biology 2006-2007

Errors of Meiosis

Chromosomal Abnormalities


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Chromosomal abnormalities

Incorrect number of chromosomes nondisjunction

chromosomes dont separate properly

during meiosis

breakage of chromosomes

deletion

duplication

inversion translocation


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Nondisjunction

Problems with meiotic spindle cause errors indaughter cells

homologous chromosomesdo not separateproperly during Meiosis 1

sister chromatidsfail to separate during Meiosis 2 too many or too few chromosomes

2n n

n

n-1

n+1


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Alteration of chromosome number


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Nondisjunction

Baby has wrong chromosome number trisomy

cells have 3 copies of a chromosome

monosomy cells have only 1 copy of a chromosome

n+1 n

monosomy2n-1

n-1 n


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Human chromosome disorders

High frequency in humans most embryos are spontaneously aborted

alterations are too disastrous

developmental problems result frombiochemical imbalance

imbalance in regulatory molecules?

Certain conditions are tolerated

upset the balance less = survivable

characteristic set of symptoms = syndrome


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Down syndrome

Trisomy 21 3 copies of chromosome 21

1 in 700 children born in U.S.

Chromosome 21 is thesmallest human chromosome

but still severe effects

Frequency of Downsyndrome correlateswith the age of the mother


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Down syndrome & age of mother

Mothers age

Incidence of

Down Syndrome

Under 30


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Genetic testing

Amniocentesis in 2nd trimester sample of embryo cells

stain & photograph chromosomes

Analysis of karyotype


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Sex chromosomes abnormalities

Human development more tolerant ofwrong numbers in sex chromosome

But produces a variety of distinct

syndromes in humans XXY= Klinefelters syndrome male

XXX= Trisomy X female

XYY= Jacobs syndrome male

XO = Turner syndrome female


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XXYmale one in every 2000 live births

have male sex organs, but

are sterile feminine characteristics

some breast development

lack of facial hair

tall

normal intelligence

Klinefelters syndrome


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Klinefelters syndrome


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Jacobs syndrome male

XYYMales 1 in 1000 live male

births

extra Y chromosome slightly taller than

average

more active

normal intelligence, slight learning disabilities

delayed emotional immaturity

normal sexual development


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Trisomy X

XXX 1 in every 2000 live births

produces healthy females

Why? Barr bodies

all but one X chromosome is inactivated


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Turner syndrome

M onosomy X or X0 1 in every 5000 births

varied degree of effects

webbed neck short stature

sterile


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Changes in chromosome structure

deletion loss of a chromosomal segment

duplication

repeat a segment

inversion

reverses a segment

translocation

move segment from one chromosome

to another

errorof

r

eplication

erro

rof

crossin

go

ver


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AP Biology 2006-2007

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5. ch15 chromosomal abnormalities.ppt

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