chapter 11.3 pg. 311. pairs of homologous chromosomes are arranged in decreasing size to produce a...
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Chromosomes and Human Heredity
Chapter 11.3Pg. 311
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Pairs of homologous chromosomes are arranged in decreasing size to produce a micrograph called a karyotype
Scientists have found that chromosomes end in protective caps called telomeres
Telomere caps consist of DNA associated with proteins
Karyotype Studies
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Telomeres also might be involved in both aging and cancer
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Cell division during which sister chromatids fail to separate properly, which does happen occasionally, is called nondisjunction
Nondisjunction can result in extra copies of a certain chromosome or only one copy of a particular chromosome
Set of 3 chromosomes of one kind is called Trisomy
Nondisjunction
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Only one of a particular type of chromosome is called monosomy
Alterations of chromosome number are associated with serious human disorders, which are often fatal
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one of the earliest known human chromosomal disorders
Result of an extra chromosome 21(trisomy 21)
Distinctive facial features, short stature, heart defects, and mental disabilities
Down Syndrome
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Frequency in the US: 1/800 children are born with Down Syndrome
Frequency also increases with increasing age of mother◦ 6% increase in chance with mothers who are 45+
www.downsyndrome.com
www.downsyndrome.com
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Couples who suspect they might be carriers for certain genetic disorders might want to have a fetal test performed
Test can only be performed if both mother and unborn child are in good health
Fetal Testing
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TEST Benefit Risk
Amniocentesis -Diagnosis of chromosomal abnormalities-Diagnosis of other defects
-Discomfort for mother-Slight risk of infection-Risk of miscarriage
Chorionic villus sampling
(placental sample)
-Diagnosis of chromosomal -Diagnosis of certain genetic defects
-Risk of miscarriage-Risk of infection-Risk of newborn limb defects
Fetal blood sampling -Diagnosis of genetic or chromosome abnormalities-Checks for fetal blood problems and O2 levels-Medications can be given to the fetus before birth
-Risk of bleeding from sample site-Risk of infection-Amniotic fluid might leak-Risk of fetal death
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