Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.
Klinefelter Syndrome. This young man exhibits many characteristics of Klinefelter syndrome: small testes, some development of the breasts, sparse body hair, and long limbs. This syndrome results from the presence of two or more X chromosomes with one Y chromosome (genotypes XXY or XXXY, for example). (Courtesy Nancy S. Wexler, PhD, Columbia University. Picked up from Patton KT, Thibodeau GA: Anatomy & physiology, ed 9, St Louis, 2016, Mosby.)
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Sex Chromosome Aneuploidy (contd) Question 3
A female has one X chromosome. Which diagnosis will the nurse observe documented on the chart?
Trisomy X syndrome
Klinefelter syndrome
Fragile X syndrome
Turner syndrome
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.
Elsevier items and derived items 2009, 2005, 2001 by Saunders, an imprint of Elsevier Inc.
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Abnormalities of Chromosomal Structure
Effects may or may not have serious consequences.
Chromosome breakage
If a chromosome break occurs, then the break is usually repaired with no damage.
Breaks can stay or can heal in a way that alters the structure of the chromosome.
Can occur spontaneously.
Agents of chromosome breakage include Ionizing radiation, chemicals, and viruses.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.
Abnormalities of Chromosomal Structure (contd)
Deletions
Chromosome breakage or loss of DNA
Example: Cri du chat syndrome or cry of the cat
Low birth weight, mentally challenged, and microcephaly
Duplications
Excess genetic material
Usually have less serious consequences
Inversion
Chromosomal rearrangement in which a chromosome segment is inverted: ABCDEFG becomes ABEDCFG
Usually affects offspring
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.
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Abnormalities of Chromosomal Structure (contd)
Infant with cri du chat (5p deletion) syndrome
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.
-Occurs as a result of deletion of part of short arm portion of chromosome 5. Although one copy of chromosome is normal, serious consequences can still occur with deletions.
-Name derived from distinctive cry of newborn with this condition,
-Other symptoms include severe mental retardation, microcephaly, heart defects, and typical facial appearance seen in figure above.
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Abnormalities of Chromosomal Structure (contd
Fragile X syndrome
Site is on the long arm of the X chromosome; has an elevated number of repeated DNA sequences.
Is associated with being mentally challenged; is second in occurrence to Down syndrome.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.
-Caused by an elevated number of repeated DNA sequences (more than 200) in the first exon of the fragile X gene. DNA replication becomes unstable, more than 20 genetic diseases are linked to this mechanism.
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Elements of Formal Genetics
Genetic inheritance
Mechanisms by which an individuals set of paired chromosomes produces traits.
Explains the patterns of inheritance for traits and diseases that appear in families.
Mendelian traits
Are inherited traits primarily attributed to single genes.
Copyright 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc.
Elements of Formal Genetics (contd)
Locus: Is the location occupied by a gene on a chromosome.
Allele: Is one of several different forms of a gene at a locus.
One member of a gene from the mother; one member of a gene from the father
Homozygous: When genes are identical
Heterozygous: When genes are different
Polymorphism or polymorphic
Is a locus that has two or more alleles that occur with appreciable frequency.
th a carrier for an autosomal dominant gene.
