Errors of Meiosis
Chromosomal Abnormalities
2006-2007


Incorrect number of chromosomes
◦ ____________________
 chromosomes don’t separate properly during meiosis
◦ breakage of chromosomes
 ___________________
 ___________________
 ___________________
 ___________________

2n

Problems with meiotic spindle cause errors in daughter cells
◦ ___________________ chromosomes do not separate properly during Meiosis 1
◦ ____________________ fail to separate during Meiosis 2
◦ too many or too few chromosomes

error in Meiosis 1 all with incorrect number error in Meiosis 2
1/2 with incorrect number


Baby has wrong chromosome number
◦ ___________________
 cells have 3 copies of a chromosome
◦ ___________________ n+1
 cells have only 1 copy of a chromosome n n-1 n trisomy
2n+1 monosomy
2n-1



High frequency in humans
◦ most embryos are spontaneously _________________
◦ alterations are too disastrous
◦ developmental problems result from biochemical imbalance
 imbalance in regulatory molecules?
 hormones?
 transcription factors?
Certain conditions are tolerated
◦ upset the balance less = __________________
◦ but characteristic set of symptoms = ________________




__________________
◦ 3 copies of chromosome 21
◦ 1 in 700 children born in U.S.
Chromosome 21 is the smallest human chromosome
◦ but still severe effects
Frequency of Down syndrome correlates with the age of the mother

Mother’s age
Under 30
30
35
36
37
38
46
48
49
39
40
42
44
Incidence of
Down Syndrome
<1 in 1000
1 in 900
1 in 400
1 in 300
1 in 230
1 in 180
1 in 135
1 in 105
1 in 60
1 in 35
1 in 20
1 in 16
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

Genetic testing



In _______________ ________________, high-frequency sound waves are directed into the pregnant woman’s abdomen.
Echo from the sounds are used to make a picture of the inner structures of the fetus.
This procedure is useful for determining the location of the fetus in the uterus, as well as to detect microencephaly (small brain), spina bifida and an abnormally small or large fetus.



__________________ in 2nd trimester
◦ sample of embryo cells
◦ stain & photograph chromosomes
Analysis of karyotype

Genetic testing

In a _____________ __________ biopsy, a small sample of placenta is taken between the 8th and 11th week of pregnancy.

A diagnosis is available within 10 days.

A source of help for prospective parents is genetic counseling.



Human development more tolerant of wrong numbers in sex chromosome
But produces a variety of distinct syndromes in humans
◦ ________ = Klinefelter’s syndrome male
◦ ________ = Trisomy X female
◦ ________ = Jacob’s syndrome male
◦ ____ = Turner syndrome female


________ 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


____________ Males
◦ 1 in 1000 live male births
◦ extra Y chromosome
◦ slightly taller than average
◦ more active
◦ normal intelligence, slight learning disabilities
◦ delayed emotional maturity
◦ normal sexual development


___________
◦ 1 in every 2000 live births
◦ produces healthy females
 Why?
 Barr bodies
 all but one X chromosome is inactivated


Monosomy ____ or _____
◦ 1 in every 5000 births
◦ varied degree of effects
◦ webbed neck
◦ short stature
◦ sterile


___________
◦ loss of a chromosomal segment

___________
◦ repeat a segment

___________
◦ reverses a segment

___________
◦ move segment from one chromosome to another

 http://www.goldiesroom.org/video_archiv e.htm
“Additions and Deletions” &
“Translocation”

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2006-2007