Chromosomes and Human Heredity

Chapter 11.3Pg. 311

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

Telomeres also might be involved in both aging and cancer

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

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

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

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

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

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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