Chapter 11 Section 3: Chromosomes and Human Heredity Ms. Diana and Ms. Su’ad

Karyotype Studies The study of genetic material does not only involve the study of genes. It also involves whole chromosomes by using images of chromosomes stained during metaphase. The staining bands identify or mark identical places on homologous chromosomes. Homologous chromosome is one of two paired chromosomes, one from each parent, that carries genes for a specific trait at the same location. The pairs of homologous chromosomes are arranged in decreasing size to produce a micrograph called a karyotype.

Karyotype Studies The chromosomes are matched together with one pair of non-matching sex chromosomes.

Telomeres Telomeres – protective caps that are found at chromosome ends. Telomeres consist of DNA and proteins. The cap is a protective part for the structure of the chromosomes. Scientists have discovered that telomeres also might be involved in both aging and cancer.

Telomeres: A Closer Look

Nondisjunction Nondisjunction – the failure of sister chromatids to separate properly during cell division. If nondisjunction takes place, then the gametes produced will not have the correct number of chromosomes. It can result in extra copies of a certain chromosome or one copy of a specific chromosome in the offspring. Set of three chromosomes: trisomy Having just one type of chromosome: monosomy

Trisomy

Down Syndrome Down syndrome is one of the earliest known human chromosomal disorders that is a result of an extra chromosome 21. “Trisomy-21” Characteristics of Down syndrome: Short stature Heart defects Mental disability

Sex Chromosomes Nondisjunction occurs in both autosomes and sex chromosomes.

Turner’s syndrome Has only 1chromosome.

Fetal Testing Fetal tests can provide important information to the parents and the physician who is treating them. Test Benefit Risk Amniocentesis Diagnosis of chromosome abnormalities Diagnosis of other defects Discomfort for expectant mother Slight risk of infection Risk of miscarriage Chorionic villus sampling Diagnosis of chromosome abnormality Diagnosis of certain genetic disorders Risk of infection Risk of newborn limb defects Fetal blood sampling Diagnosis of genetic or chromosome abnormality Checks for fetal blood problems and oxygen levels Medications can be given to the fetus before birth Risk of bleeding from sample site Amniotic fluid might leak Risk of fetal death

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