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Pathophysiology Chapter 6 Genetic and Developmental Disorders

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heredity
The passage of characteristics from parent to offspring.
DNA
Deoxyribonucleic acid. A type of nucleic acid that contains a sugar (deoxyribose). Responsible for storage of genetic information.
What are the nitrogenous bases that make up DNA?
adenine and guanine (purines); cytosine, thymine (pyrimidines).
base pairs
A-T and C-G combinations that link the two strands of DNA.
genes
Small functional hereditary units located on a specific site on a chromosome that are made up of pieces of DNA. They contain the information (genetic code) for making a specific protein.
codon
A fundamental triplet code necessary for protein synthesis. Made up of three nitrogenous bases.
amino acids
The basic compounds produced by codons that form the basis of human proteins.
ribonucleic acid
RNA. Single-stranded nucleic acid that contains the sugar ribose
What are the base pairs of RNA?
Adenine-Uracil, Cytosine-Guanine.
messenger RNA
mRNA. Template for protein synthesis that depends on a codon sequence that is based on that of the complementary strand of DNA.
transfer RNA
tRNA. Each recognizes and binds a specific amino acid, which it then transfers to ribosomes.
ribosomal RNA
type of RNA that makes up the major part of ribosomes. Associated with mRNA in the translation of the genetic code.
chromosomes
Double-stranded DNA containing threadlike sections of genes. Most commonly found in the nucleus.
mitosis
Cell division in which the nucleus divides into nuclei containing the same number of chromosomes
diploid
The number of chromosomes the human somatic body cell contains. It is 46 (23 pairs).
autosomes
chromosomes other than sex chromosomes
sex chromosomes
X and Y. The genetic determinants of the sex of an individual.
gametes
Ova and sperm. Contain only one of the chromosome pairs, known as the haploid number.
meiosis
Process of cell division where one cell produces four cells, each with half the number of chromosomes, known as gametocytes.
transcription
transfer of genetic code from one type of nucleic acid to another.
genomics
Study of the human genome
nutrigenomics
The study of how nutrition interacts with specific genes to influence a person's health
pharmacogenetics
interactions between drugs and the genome that affect the efficacy or toxicity in the human response
genotype
the genetic makeup of an individual.
phenotype
The genetic traits that are observable or apparent
alleles
A series of two or more different genes occupying the same location on a specific chromosome.
polygenic
genetic traits resulting from the interaction of several genes. Influenced by environmental factors.
mutations
errors in DNA duplication
somatic mutation
A mutation that is not inheritable.
polymorphism
gene occurring in more than one form (ie, having one brown eye and one blue eye)
expressivity
the degree to which a gene is expressed in an individual's phenotype
penetrance
the ability of a gene to express a mutation
single gene traits
traits passed on by transmission of a single gene.
homozygous
identical alleles on each chromosome
heterozygous
two different alleles on each chromosome
Mendelian pattern
predictable trait transmission based on autosomal dominant or recessive genotypes.
dominant genes
genes more likely to be expressed
recessive genes
less influential genes. Require homozygous alleles to be expressed.
sex-linked traits
traits passed on by sex chromosomes
Single gene disorders occur at a specific, single site on the strand of DNA as a result of the following:
Deletion, duplication, inversion, insertion, translocation
autosomal dominant disorder
disorder where the abnormal allele is dominant, normal allele is recessive, and the genes exist on a pair of autosomes. HD, Marfan syndrome, and osteogenesis imperfect are examples of autosomal dominant disorders.
autosomal recessive disorder
disorder caused by mutated gene which is recessive; only homozygous recessive individuals express disorder. Examples are cystic fibrosis, Tay-Sachs disease, and sickle cell disease.
carriers
individuals who are heterozygous for a recessive gene mutation.
sex-linked disorders
disorders caused by mutations of genes located on the sex chromosomes. Examples are hemophilia and XSCID (bubble boy disease)
matrilineal inheritance pattern
pattern where mitochondrial genes are transmitted through maternal lines. Example: Leigh syndrome
heteroplasmy
the random distribution of mitochondria to daughter cells during embryonic cell division, leading to a variable distribution of mutant mitochondrial genes in tissues of an individual and between related individuals.
polygenic inheritance
results from multiple alleles at different loci affecting phenotype. Both genes and environment are factors. Examples: height
chromosomal alterations
loss, addition, or rearrangement of genetic material
karotype
a picture of arranged, paired, like chromosomes in order of largest to smallest
nondisjunction
An unequal number of chromosomes between cells as a result of chromosomes failing to separate
mosiacism
the combination of cells with the regular chromosome number and those with an altered number of chromosomes.
monosomy
condition where nondisjunction results in cells with one copy of a chromosome instead of two. If this occurs with autosomes, it is not compatible with life
trisomy
the presence of three copies of a chromosome in a cell. Viability of individual depends on chromosome affected. Downs Syndrome is an example.
translocation
abnormality where a large segment of DNA breaks from one chromosome and reattaches to another. Often occurs during meiosis
epigenetic
around the genome. Modifications of gene expression caused by environmental and metabolic agents that stimulate chemical modifications of genes.
genomic imprinting
mechanism that controls expression of genes based on parental origin. It is an epigenetic phenomenon resulting in regulation of expression of gene activity without alteration of gene structure.
Why does genomic imprinting occur?
DNA methylation preventing transcription of the gene. Occurs when both maternal and paternal alleles are present with only one allele expressed and the other inactive. Ex.-MMD, Fragile X Syndrome, Wilms tumor, osteosarcoma, bilateral retinoblastoma.
developmental disorders
disorders as a result of environmental influences, such as drugs, hormones, pathogens, and chemicals, that alter gene function
When is risk of damage to a developing child the greatest?
3 to 8 weeks
organogenesis
development of organ systems
teratogens
substances that cause damage to developing embryos or fetuses
FAS
fetal alcohol syndrome. A condition characterized by significant mental handicap, growth deficit, and physical disability caused by maternal alcohol consumption during pregnancy.
TORCH
toxoplasmosis, other (hepatitis), rubella, cytomegalovirus, herpes. The group of diseases known to cause damage to a fetus if exposure occurs.
congenital defects
defects as a result of maternal nutrient deficiency
NTD
neural tube defect
preimplantation genetic diagnosis
identification of abnormalities before implantation by using in vitro fertilization, embryo culture, and biopsy of the blastomere (early embryo)
aneuploidy
abnormal chromosome number
HD
Huntington's Disease. A neurologic disorder caused by degeneration of the basal ganglia and cortical regions of the brain. Clinical manifestations include involuntary movements, cognitive impairment, loss of memory, antisocial and impulsive behaviors, and eventually, intellectual deterioration, paranoia, and delusions.
sickle cell anemia
An autosomal recessive disorder affecting RBCs where Hemoglobin A in the RBCs is replaced by hemoglobin S, which distorts and stiffens RBCs and reduces their life span. There is splenic trapping and destruction of RBCs, decreased oxygenation, and damage to endothelial cells lining blood vessels. Clinical manifestations include anemia, jaundice.
hemolysis
breakdown of RBCs
sickle cell trait
disorder in which individuals show signs of mild anemia only when they are seriously deprived of oxygen; occurs in individuals who have one dominant allele for normal blood cells and one recessive sickle-cell allele
bilirubin
yellow, lipid-soluble by-product of hemoglobin as a result of RBC damage.
How is sickle cell anemia diagnosed?
Hemoglobin electrophoresis, isoelectric focusing, high-performance liquid chromatography, DNA analysis
MELAS
mitochondrial encephalomyopathy, lactic acidosis, and stroke. A mitochondrial gene disorder
What are the clinical manifestations of MELAS?
Stroke-like episodes in people younger than 40, encephalopathy, including seizures and dementia, and lactic acidosis. Hearing loss, blindness, migraine, vomiting, hemiplegia, cardiomyopathy.
COX
cytochrome oxidase. Enzyme important in catalyzing oxidation-reduction mitochondrial reactions in cellular respiration
Down syndrome
Genetic birth defect caused by alteration in chromosome number (autosome). There is trisomy at chromosome 21. Clinical manifestations are mental retardation, intestinal malformations, visual and hearing impairment, cardiac defects.
NT
nuchal translucency, or thickness at the nape of the neck of a fetus. Increased NT may signify Down syndrome.
Turner syndrome
Disorder caused by alteration in chromosome number (sex chromosome). Found in females. Results from loss of all (monosomy) or part of the sex chromosome X. Clinical manifestations include: Short stature, gonadal failure, short fingers, short neck, cleft palate, cardiac and kidney abnormalities, hearing loss, webbed neck, low hairline, lymphatic obstruction, reproductive defects. Deafness, osteoporosis, hypothyroidism in adult women.
KS
Klinefelter syndrome. XXY disorder in males. Clinical manifestations: Infertility, scant pubic hair, atrophic testes, small penis.
hygroma
cyst with diameter larger than biparietal diameter of the head.
Fragile X Syndrome
Sex-linked genetic disorder. Defect is located on X chromosome. Follows Mendelian inheritance pattern. Clinical manifestations: Connective tissue problems, enlarged testicles, cognitive impairment, behavioral difficulties, premature ovarian failure
CVD
Cardiovascular disease. A multifactorial inheritance disease. Caused by mutation in genes regulating uptake of cholesterol from blood (LDL receptor [LDLR] autosomal recessive hypercholesterolemia [ARH] genes), binding of apoliprotein B-100 to the LDLR, synthesis and clearance of cholesterol (ABCG5 and ABCG8 genes).
NTD
Neural tube defect. A developmental maladaptation. Incomplete closure of neural tube during embryonic life. Includes spinal bifada and anencephaly.
anencephaly
closure defect in skull area, with all or part of the top of the skull and portions of brain missing.
spinal bifada
spinal bifada occulta: incomplete closure of vertebrae with no protrusion of meninges or spinal cord
meningocele: incomplete closure with protrusion of meninges and cerebrospinal fluid
myelomeningocele: incomplete closure with protrusion of meninges, cerebrospinal fluid, and spinal cord/nerve roots.