Term
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Definition
| The two members of a gene pair, one inherited from the mother and the other from the father. |
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Term
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Definition
| Any chromosome other than a sex chromosome. 22 pairs have the same appearance in all individuals, and each has been given a numeric designation for classification purposes. |
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Term
| Autosomal Dominant Disorders |
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Definition
| A single mutant allele from an affected parent is transmitted to an offspring regardless of sex. Due to mutation of a specific autosomal gene: males/females equally affected; usually 1 affected parent; unaffected individuals do not transmit disease; offspring of 1 affected parent with unaffected mate (1:2 chance of inheritance); offspring of 2 affected parents (3:4 chance). The affected parent has a 50% chance of transmitting the disorder to each offspring. This disorder may manifest as a new mutation. Age of onset- delayed, signs & symptoms appear later in life, as in Huntington's chorea. The mutation depends on the afected person's reproductive capacity. If the defect does not affect reproductive capacity, it is more likely to be inherited. |
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Term
| Autosomal Recessive Disorders |
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Definition
| Disorder that is manifested only when both members of the gene pair are affected. Both parents may be unaffected but are carriers of the defective gene. Affects both sexes. Age of onset- early in life, characteristically caused by loss-of-function mutations. Includes almost all inborn errors of metabolism. Ex: phenylketonuria, lysosomal storage diseases, cystic fibrosis and Tay-Sachs. |
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Term
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Definition
| Most genetic information of a cell is organized, stored, and retrieved in the small intracellular structures. Visibly only in dividing cells, they retain their integrity between cell divisions. Arranged in pairs; one member of the pair is inherited from the father, the other from the mother. 46 single or 23 pairs present. Of the 23 pairs, 22 are called autosomes (homologous) and are alike in both males and females, remaining pair are sex chromosomes (female- 2X chromosomes, one from each parent- homologous; male- 1X and 1Y chromosome, one from each parent- hemizygous). Characterized by total size, length of arms x, karotype (an individuals chromosomal complement, test to evaluate chromosomes- banding patterns when exposed to stain). |
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Term
| Chromosomal Abnormality Disorders |
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Definition
| Account for a large proportion of reproductive wastage (early gestational abortions), congenital malformations, and mental retardation. More than 60 identifiable syndromes that are present in 0.7% of all live births, 2% of all pregnancies in women older than 35, and 50% of all first-term abortions. |
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Definition
| Defects that are present at birth, although they may not be present until later in life. May be caused by genetic influences, environmental factors or a combination of both. |
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Term
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Definition
| Genetic composition of a person. Genetic information stored in the base sequence triplet code. Often not evident by available detection methods. Unique genetic makeup. Resulting of 23 maternal and 23 paternal chromosomes uniting at conception. |
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Term
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Definition
| Members of a gene pair are different. One member of the gene pair codes for the trait, said to be dominant. |
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Definition
| Members of a gene pair are identical (code for the exact same gene product). Both members of the gene pair code for the trait, said to be recessive. |
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Term
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Definition
| Type of cell division, limited to replicating germ cells and takes place only once in a cell line. Results from the formation of gametes or reproductive cells (ovum and sperm), each of which has only a single set of 23 chromosomes. Divided into 2 phases: I- Homologous chromosomes approach each other and pair; paired chromosomes interchange chromatid fragments; double-structured chromosomes pull apart; Anaphase- first division (two cells each with 46 chromosomes, 2 or 3 crossover events occur). Second division- sister chromatids pulled apart, result is 4 haploid cells with 23 chromosomes. II- Double structured chromsomes pull apart at the centromere to form four single-stranded chromosomes (reductive division). Two germ cells (egg and sperm) combine to form a cell with 46 chromosomes. Haploid- each germ cell contributes 23 chromosomes. Involves two divisions of chromosomal DNA. Duplicated sister chromatids make contact with their homologous pairs. Crossing over- portions of homologous chromosomes exchange to form new combination of genes within chromosomes. |
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Term
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Definition
| Presence of only one member of a chromosome pair. The defects of the autosomes are severe and usually cause abortion. Of the X chromosomes or Turner syndrome, causes less severe defects. Daughter cell with a deficiency of 1 chromosome, not compatible with life. |
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Term
| Multifactorial Inheritance Disorders |
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Definition
| Caused by multiple genes and, in may cases, environmental factors. Expressed during fetal life, at birth, or later in life. Ex: cleft lip or palate, clubfoot, congenital dislocation of the hip, congenital heart disease, pyloric stenosis, and urinary tract malformation. Environmental factors that develop in adult life: congenital artery disease, diabetes mellitus, hypertension, cancer, and common psychiatric disorders such as bipolar and schizophrenia. Traits cannot be predicted, characteristic patterns exist. Tend to involve a single organ or tissue derived from the same embryonic developmental field. Risk of recurrence in future pregnancies is for the same or a similar defect (parents of a child with cleft palate have an increased risk of having another child with cleft palate). Increased risk with first-degree relatives of the affected person. Risk increases with increasing incidence of the defect among relatives. Risk increases when the defect occurs in the sex not usually affected by the disorder. |
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Term
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Definition
| Recognizable traits, physical or biochemical, associated with a specific genotype. Observable expression of a genotype in terms of morphologic, biochemical, or molecular traits. Outward apparent physical and biochemical attributes. |
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Definition
| The possible combinations that can occur with transmission of single-gene dominant and recessive traits. Main purpose is predictability. Shows predictable patterns in transmission of single-gene traits from parents to offspring. Dominant allele (indicated by capital letter)- trait apparent and will mask recessive allele, often codes for functional enzymes or structural proteins. Recessive allele (indicated by lowercase letter)- trait apparent only if both alleles are recessive, often codes for nonfunctional enzymes or structural proteins. Based on principle that all genes are: independent, inherited in an individual manner. Both parents heterozygous for dominant trait (Aa): 25% probability of AA; 50% probability of Aa (trait expressed in same manner, an individual usually is carrier of disease). 25% probability of aa (trait absent, many diseases carried in recessive allele). |
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Term
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Definition
| Also called Mendelian disorders. Caused by a mutant allele at a single gene locus and follow mendelian patterns of inheritance (include autosomal dominant and recessive traits that are transmitted from parents to their offspring in a predictable manner). Primarily disorders of pediatrics. Characterized by their patterns of transmission. Patterns of inheritance depend on whether the gene is located on an autosomal or sex chromosome. Lead to a formation of an abnormal protein or decreased production of a gene product. |
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Term
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Definition
| Agents such as radiation, chemicals and drugs, and infectious organisms are agents that produce abnormalities in the developing embryo. The period during which the embryo is most susceptible to these agents is the same time during which rapid differentiation and development of body organs and tissues are taking place, usually from days 15-60 postconception. Fetal Alcohol Syndrome is a risk for infants of women who regularly consume alcohol during pregnancy. Folic Acid deficiency can contribute to to neural tube defects. Toxoplasmosis, other, rubella- German measles, cytomegalovirus, and herpes, which are the infectious aents most frequently implicated in fetal anomalies (TORCH). |
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Term
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Definition
| Presence of more than two chromosomes to a set, occurs when a germ cell containing more than 23 chromosomes is involved in conception. |
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Term
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Definition
| Sex-linked disorders are almost always associated with the X, or female, chromosome, and the inheritance pattern is predominantly recessive. Females express disease when both X chromosomes have mutation. Males always express disease (only have one X chromosome). All males who receive the gene are typically affected. Unaffected mother carries one normal and one mutant allele on the X chromosome 50% chance of transmitting the defective gene to her sons, daughters have a 50% chance of being carriers of the mutant gene. Affected son procreates, daughters become carriers of mutant gene; does not transmit gene to sons. Carrier female has 1:2 chance of producing an affected son or carrier daughter. Females rarely affected: homozygous state of affected or carrier mother, and affected father. Example: hemophilia A. |
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Term
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Definition
| Autosomal dominant disorder of the connective tissue, which gives shape and structure to other tissues in the body and holds them in place. Affects several organ systems (eyes, heart and blood vessels, bone and joints). May have abnormalities of one or all three systems. Skeletal most obvious: long, thin body with exceptionally long extremities and long, tapering fingers (arachnodactyly or spider fingers); kyphosis and scoliosis. Cardiovascular lesions most threatening. Aorta tends to be weak, susceptible to dilation/rupture. Traced to mutations in fibrillin 1 gene on chromosome 15. |
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Term
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Definition
| Trisomy 21. Autosome disorder. Caused by a nondisjunction or an error in cell division during meiosis, resulting in a trisomy of chromosome 21. Condition usually apparent at birth. Features: growth failure and a small square head; flat facial profile, small nose and depressed nasal bridge; small folds on the inner corners of the eyes (epicanthal folds) and upward slanting of the eyes; small, low-set, and malformed ears; fat pad at the back of the neck; open mouth; large, protruding tongue; hands, short and stubby with fingers that curl inward with a single palmar crease (simian); excessive space between large and second toes. Often accompanied by congenital heart defects and increased risk of GI malformations. Greater risk of acute leukemia, respiratory infections and alzhemier's. Prenatal screen: Alpha-fetoprotein, hCG, unconjugated estriol, inhibin A, and pregnancy-associated plasma protein A (PAPP-A). Fetal nuchal translucency (sonolucent space on the back of fetal neck) 10-13 weeks gestation. Accurately determine: chorionic villus sampling, amniocentesis, or percutaneous umbilical blood sampling. Extra 21st chromosome. Most common chromosomal disorder. Leading cause of mental retardation. Majority of fetuses either stillborn or aborted. |
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Definition
| Disorder involving sex chromosomes. Condition of testicular dysgenesis accompanied by the presence of one or more extra X chromosomes in excess of the normal male XY complement. Lack of secondary sex characteristics during puberty. Cause is unknown, advanced maternal age increases risk. Characterized by enlarged breasts, sparse facial and body hair, small testes, and the inability to produce sperm. Infertility is common. Associated symptoms: lack of testosterone, testicular atrophy (infertility), feminine hair distribution/gynecomastia, tall stature (long arms/legs), high-pitched voice, impaired intelligence. Testosterone therapy usually indicated. |
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Definition
| Primarily affects neurologic function. Symptoms appear after age 40. Mental deterioration, involuntary arm/leg movements. Parent may transmit to offspring before becoming aware of defective gene. Hereditary disorder characterized by chronic progressive chorea, psychological changes, and dementia. Autosomal dominant disorder, age of onset- 4th and 5th decades. Localized death of brain cells. Imbalance of dopamine and acetylcholine may contribute to manifestations of the disease. No cure. Discovery of a gene locus has enabled testing that can predict whether a person will develop the disease. |
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Definition
| Disorder of sex chromosome. (1:3000 births) Absence of all or part of the X chromosome. Almost all fetuses with this karotype are spontaneously aborted during the first trimester. Characteristically, a girl will be short in stature, but body proportions are normal. Female phenotype with absence of ovaries or fibrous ovaries, does not menstruate (amenorrhea) and no signs of secondary sex characteristics. Webbing of the neck with redundant skin folds, nonpitting lymphedema of the hands and feet, sterility, wide chest and congenital heart defects. Monosomy X: 1 normal X chromosome; no Y chromosome. Second X chromosome missing or structurally abnormal; usually due to father's advanced age. Rarely survive to birth. |
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Term
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Definition
| Autosomal recessive disease involving fluid secretion in the exocrine glands in the epithelial lining of the respiratory, GI, and reproductive tracts. Manifested by pancreatic exocrine deficiency and elevation of sodium chloride in the sweat. Nasal polyps, sinus infections, pancreatitis, and cholelithiasis are common. |
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Definition
| Autosomal recessive disorder. Deficiency of the liver enzyme phenylalanine hydroxylase. Toxic levels of amnio acid and phenylalanine accumulate in the blood and other tissues. Untreated: mental retardation, microcephaly, delayed speech. Newborn infants routinely screened for abnormal levels of serum phenylalanine, PKU screening obtained at least 12 hours after birth to ensure accuracy. Infants with the disorder are treated with a special diet that restricts phenylalanine intake, diet can prevent mental retardation. Treatment 7-10 days of age. |
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Definition
| Autosomal recessive disorder. Red blood cell defect. |
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Definition
| X-linked recessive disorder. Bleeding disorder |
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Term
| Familial Hypercholesterolemia |
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Definition
| Autosomal dominant disorder. Premature atherosclerosis |
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Term
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Definition
| Males and females are equally affected (have the disease). May skip generations. Normal siblings of affected individuals do not pass the trait on to their offspring. Only one mutated copy of the gene is needed for a person to be affected by an Autosomal dominant disorder. Each affected person usually has one affected parent. A child will have a 50% chance of inheriting the mutated gene from a heterozygous parent. Examples include: Huntington disease and Marfan's Syndrome. |
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Term
| Autosomal Recessive Genes |
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Definition
| Males and females are equally affected (have the disease). Heterozygous individuals are carriers and usually asymptomatic. Affected individuals will have unaffected parents who are heterozygous for the trait (parents will pass on the disease, but not suffer from it themselves). Offspring of heterozygous parents have a 25% chance of being affected. Offspring of heterozygous parents have a 50% chance of being carriers. A negative family history for the disease usually exists. Two copies of the gene must be mutated for a person to be affected by an Autosomal recessive disorder. An affected person usually has affected parents who each carry a single copy of the mutated gene and are referred to as carriers. Two unaffected people who each carry one copy of the mutated gene have a 25% chance with each pregnancy of having a child who is affected by the disorder. Examples: Cystic Fibrosis, Sickle Cell Anemia. |
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Term
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Definition
| Some conditions are caused by genes located in sex chromosomes and this makes the inheritance sex-linked. The mutant gene is usually present on the X chromosome. Males are more frequently affected than females. X-linked recessive is more common than X-linked dominant (very rare). Most common is an affected male who does not pass the gene to his son. Daughters of an affected male may be carriers, but rarely ever have the disease. Males are never carriers. Females who carry an X-linked recessives disorder have a 50% chance of having sons who are affected and a 50% chance of having daughters who carry one copy of the mutated gene. Examples: Hemophilia A and Duchenne's Muscular Dystrophy. |
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Term
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Definition
| The study of heredity and its variations. Biochemical: study of the impact of genes on enzymes and the cellular reactions they catalyze. Clinical: Study and use of genetics in health and disease. Molecular: study of molecular structure of genes and their cellular and subcellular functions. |
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Term
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Definition
| Having an abnormal number of chromosomes. Causes: failure of the chromosomes to seperate during oogenesis or spermatogenesis. Can occur in either the autosomes or sex chromosomes, and is called nondisjunction. Nondisjunction gives rise to germ cells that have an even number if chromosomes. |
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Definition
| Constellation of physical, behavioral, and cognitive abnormalities resulting from maternal alcohol consumption. Prenatal or postnatal growth retardation; CNS involvement, including neurologic abnormalities, developmental delays, behavioral dysfunction, intellectual impairment, skull and brain malfunction; characteristics of set facial features: small palpebral fissures (eye openings), thin vermilion border (upper lip), elongated, flattened midface and philtrum (groove in the middle of upper lip), microcephaly, epicanthal folds, small chin, short nose. |
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Term
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Definition
| Genes that code for a particular trait: located at a particular position on chromosomes, come in several alleles. Two alleles for each gene (one from each parent): both identical-homozygous trait; both different- heterozygous trait. |
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Term
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Definition
| Codominant: allelels not clearly dominant or recessive (blood type). Monogenic traits: result from interaction of 1 gene loci. Polygenic traits: result from interaction of several gene loci- inheritable, difficult to predict, affected by environmental factors. |
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Term
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Definition
Mutation: permanent change in DNA structure; rare; potential mutagens- radiation, chemicals, viruses.
Single-stranded breaks are easily repaired.
Double stranded breaks may result in permanent loss of genetic information at break point.
Two types: Point Mutation and Frameshift Mutation. Single-gene (Mendelian) disorders: due to DNA mutation that codes for a particular protein. Chromosome structures: also mutated through loss, gain, or translocation of segments. |
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Term
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Definition
| Single base pair substitution. May cause affected codon (three base pairs) to signify an abnormal amino acid. |
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Definition
| Often dramatically changes genetic code. Addition/removal of one or more bases changes reading frame. All remaining codon triplets have greatly altered amino acid sequences. |
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Term
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Definition
| Apparent at birth or later in life. Majority inherited from parents, some from fetal development mutations: chromosomal aberrations, mendelian single-gene disorders. Multifactorial/polygenic disorders. Fourth group: single gene but doesn't follow Mendelian pattern: triplet-repeat mutations, mitochondrial mutations, mutations affected by genomic imprinting. |
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Term
| Chromosomal Abnormalities |
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Definition
| Generally due to abnormal number of chromosomes or alterations to the structure of one or more chromosomes. Usually a result of seperation or crossing over during meiosis or mitosis. Aneuploidy: abnormal number of chromosomes, either > or < 46 in humans. Nondisjunction: failure of pairs to sperate properly during 1st or 2nd meiotic division. Resulting germ cells have 22 and 24 chromosomes, respectively. Combination of abnormal and normal germ cells produce fertilized cell with 25 or 27 chromosomes. Anaphase lag: 1 chromosome left out newly formed cell nucleus. |
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Definition
| Daughter cell with too many chromosomes. May result in viable fetus. Nearly always associated with severe disability. Those involving extra/missing sex chromosome not as debilitating. Causes: poorly understood, radiation, viruses, chemicals implicated. Increased risk: advanced maternal age, abnormalities in parental genetic structure. |
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Term
| Abnormal Chromosomal Structure |
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Definition
| Usually due to breakage and loss of rearrangement of chromosome pieces during meiosis or mitosis. Meiosis: crossing over errors- chromosome portions lost, attached upside-down, or attached to wrong chromosome. Mitosis: opportunities for chromosomal breakage and impairment. Translocation: exchange of DNA pieces between nonhomologous chromosomes; recipricol translocation- no lost genetic material, sometimes no symptoms, increased risk of producing abnormal gametes; robertsonian translocation- exchange of 1 long chromatid arm for 1 short arm. Isochromosomes: 2 identical short chromatid arms and 2 long chromatid arms remain together due to incorrect seperation at centromere. Inversion: removal and upside-down reinsertion of a chromosome; no net loss/gain of genetic material; often no significance to individual, but may affect offspring; inverted chromosome may not pair properly during meiosis, resulting in duplication or loss of genes. Deletion: loss of chromosomal material; caused by break in arm of a single chromosome; results in DNA fragment with no centromere; piece lost in next cell division; associated with some forms of cancer; deletions at both ends may form a ring chromosome. Duplication: results in extra copies of a portion of DNA; less severe consequences. |
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| Other Autosomal Chromosome Disorders |
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Definition
| Trisomy 18 (Edwards Syndrome) and Trisomy 13 (Patau Syndrome). Much less common than Trisomy 21. Severe mental retardation. Infants usually die a few weeks after birth. Trisomies 8, 9, and 22 are extremely rare. Cri du Chat Syndrome: deletion of short arm of chromosome 5; severe mental retardation, round face, congenital heart abnormalities; cry resembles a cat crying; some live to adulthood and thrive better than those wih trisomies. |
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Term
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Definition
| Multiple X Females (XXX): menstrual abnormalities; retardation tendency with more than 4X chromosomes. Double Y Males (XYY): generally taller than average. |
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Term
| Mendelain Single-Gene Disorders |
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Definition
| Result from alterations or mutations of single genes. Affected genes may code for abnormal enzymes, structural or regulatory proteins. Pedigree may help trace transmission through the family. Classified according to location of defective gene and mode of transmission- autosomal dominant, autosomal recessive, sex-linked (X-linked). |
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| NonMendelian Single-Gene Disorders |
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Definition
| Categories: caused by long triplet repeat mutations, such as fragile X syndrome; due to mitochondrial DNA mutations; associated with genomic imprinting. Triplet Repeat Mutations: fragile X syndrome (prototypical example); long repeating sequence of 3 nucelotides (CGG); premutation- possible to have an intermediate number of inherited repeats, thus increasing risk of mutation; males more severely affected. Mitochondrial Gene Mutations: tend to cause dysfunction in tissues with high utilization of ATP (nerve, muscle, kidney, liver); exhibit tricky inheritance patterns; very rare. Genomic Imprinting: process whereby maternal and paternal chromosomes are marked differentially within the cell; two differnet syndromes resulting from the same mutation (one mutation inherited from maternally derived chromosome and another from paternally derived chromosome) |
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Term
| Multifactorial (Polygenic) Disorders |
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Definition
| "Run in families". Thought to be produced by an interaction of many genes. Also present range of severity. Difficult to predict based on family history. Very common (high blood pressure, cancer, diabetes). Height, weight, intelligence. |
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Term
| Environmentally Induced Congenital Disorders |
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Definition
| Errors in fetal development that result in congenital malformations. Teratology: study of developmental anomalies. Numerous environmental influences (teratogens) may adversely affect developing fetus- chemicals, radiation, viral infections. Susceptibility depends on amount of exposure. Periods of Fetal Vulnerability: before 3rd gestational week- teratogen exposure either damages very few cells or so many that embryo cannot survive; 3rd to 9th week- embryo very susceptible to teratogenesis (especially 4th and 5th weeks during organ development); after 3rd month, teratogens affect growth or injury to already-formed organs. Other infancy disorders: generally arise later in uterine life; usually involve health of mother or placenta. |
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Term
| Diagnosis, Counseling, and Gene Therapy |
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Definition
| Prenatal Diagnosis and Counseling: maternal age >34; Chromosomal disorder in previous pregnancy; known family history of x-linked disorders; known family history of inborn errors of metabolism; neural tube anomalies in previous pregnancy; known carrier for recessive genetic disorder; ultrasound; amniocentesis; chorionic villus sampling; embryoscopy. Genetic Analysis and Therapy: treat genetic disease by replacing defective gene with healthy gene. Recombinant DNA Technology. |
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