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.

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