errors of meiosis chromosomal abnormalities · ap biology nondisjunction problems with meiotic...

2006-2007AP Biology

Errors of MeiosisChromosomal Abnormalities

AP Biology

Changes in chromosome structure deletion

loss of a chromosomal segment duplication

repeat a segment inversion

reverses a segment translocation

move segment from one chromosometo another

erro

r of

repl

icat

ion

erro

r of

cros

sing

ove

r

AP Biology

Chromosomal abnormalities Incorrect number of chromosomes

nondisjunction chromosomes don’t separate properly

during meiosis breakage of chromosomes

deletion duplication inversion translocation

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Nondisjunction Problems with meiotic spindle cause errors in

daughter cells homologous chromosomes do not separate

properly during Meiosis 1 sister chromatids fail to separate during Meiosis 2 too many or too few chromosomes

2n n

n

n-1

n+1

AP Biology

Alteration of chromosome number

AP Biologytrisomy

2n+1

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 from

biochemical 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

1 in 12491 in 16481 in 20461 in 35441 in 60421 in 105401 in 135391 in 180381 in 230371 in 300361 in 400351 in 90030

<1 in 1000Under 30

Incidence ofDown SyndromeMother’s age

Rate of miscarriage due toamniocentesis: 1970s data

0.5%, or 1 in 200 pregnancies

2006 data<0.1%, or 1 in 1600 pregnancies

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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 of

wrong numbers in sex chromosome But produces a variety of distinct

syndromes in humans XXY = Klinefelter’s syndrome male XXX = Trisomy X female XYY = Jacob’s syndrome male XO = Turner syndrome female

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XXY male 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

Klinefelter’s syndrome

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Klinefelter’s syndrome

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Jacob’s syndrome male XYY Males

1 in 1000 live malebirths

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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Examples of Chromosome Mutations Polyploidy

• Whole extra set of chromosomes• Treat cells with colchicine - freezes

metaphase• Effects in plants

Bigger, better, hardier, more diseaseresistant

• Effect in animals lethal

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Examples of Gene MutationsName of Disorder

Cystic Fibrosis

Symptoms

• Produce thick, sticky mucus thatclogs lungs and preventsenzymes from going frompancreas to intestine

• More prone to respiratoryinfection and digestive difficulty

• Can be fatal

AP Biology


Sickle CellAnemia

Symptoms

• Red blood cells mis-shaped socarry less oxygen

• Effects bone, brain & kidneys

• Homozygous(S’S’) =lethal

• Heterozygous(S’S)=better able tosurvive malaria (more prevalentin warm climates/African decent)

• Incomplete dominance

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PKU(Phenylketonuria)

Symptoms

• Inability to produce an enzymethat breaks down phenylalanine

• Effects mental development

• Treatment: no intake of food thatcontains phenylalanine (milk)

• Detected by a blood test at birth

AP Biology


Tay Sachs

Symptoms

• Lack of enzyme to break downcertain fat

• Effects: failure of proper nervoussystem development

• Treatment: none Usually lethal

• Detected by a blood test at birth orgenetic testing of parents

• Common in people of EasternEuropeans Jewish decent

AP Biology


Diabetesmellitus

Symptoms

• Failure to produce enough insulin

• Effects: too much sugar in blood, notenough in cells. Can affect kidney,eye sight, etc

• Treatment: insulin injections

• Detected by sampling urine forpresence of sugar

• Influenced by weight, diet, age, etc

AP Biology


Hemophilia(bleeder’sdisease)

Symptoms

• Lack of certain proteins which act asclotting factors and prevent bleedingto death

• Effects: can bleed to death fromsimple cut or bruise

• Treatment: transfusions of clottingfactor

• Sex linked, carried on Xchromosome

AP Biology


Color Blindness

Symptoms

• Lack certain types of color vision

• Sex linked, carried on Xchromosome

AP Biology


MuscularDystrophy

Symptoms• progressive weakness and

degeneration of the skeletalmuscles which control movement.

• Several different kinds -Duchenne’s is sex linked

AP Biology


Huntington’s

Symptoms• degeneration of brain

cells(neurons), in certain areasof the brain.

• This degeneration causesuncontrolled movements,

• loss of intellectual faculties,• and emotional disturbance.• Symptoms are not noticeable until

mid forties• Genetic testing is available for this

allele

errors of meiosis chromosomal abnormalities · ap biology nondisjunction problems with meiotic...

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