231 - Abnormal Cell - Ch. 9 Genetics

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allele

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any one of two or more alternate forms of a gene at the same location. An allele for each gene is inherited from each parent

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autosome

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a single chromosome from any of the 22 pairs of chromosomes not involved in sex determination (XX or XY)

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carrier

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person who is heterozygous; possessing two differnt alleles of a gene pair

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chromosome

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microscopic structures in the cell nucleus that contain genetic information and are constant in number in a species

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DNA

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the primary genetic material in humans consisting of nitrogenous bases, a sugar group, and phosphate combined into a double helix

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diploid

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the number of chromosomes normally present in somatic cells. for humans, 46.

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dominant

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a genetic trait that is normally expressed when a person has a gene mutation on one of a pair of chromosomes and the "normal" form of the gene is on the other chromosome

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genetics

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the scientific study of heredity; how specific traits or predispositions are transmitted from parents to offspring

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genome

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the total genetic complement of an individual genotype

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genomics

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the study of the human genome including gene sequencing, mapping, and function

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genotype

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the genes and the variations therein that a person inherits from his or her parents

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haploid

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the number of chromosomes present in egg or sperm (gametes); in humans, this is 23

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Human Genome project

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an international research efort aimed at identifying and caracterizing the order of every base in the human genome

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meiosis

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the reduction division of diploid egg or sperm (germ cells) resulting in haploid gametes (having 23 chromosomes each)

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mitosis

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cel division occurrin gi n somatic cells that normally results in daughter cells with the same number of chromosomes - 46 (diploid)

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monosomy

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missing one of a chormosome pair in normally diploid cells (for example, 45, X females have only one X chromosome)

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mutation

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a heritable alteration in the genetic material

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nondisjunction

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the faiulre of a chromosome pair to separate appropriately during meisosis, resulting in abnormal chromosome numbers in reproductive cells (gametes)

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nucleotide

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a nucleic acid "building block" composed of a nitrogenous bvase, a five-carbon sugar, and a phosphate group

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pedigree

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a diagrammatic representation of a family history

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penetrance

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the percentage of individuals known to carry the gene for a trait who actually manifest the condition. For example, a trait with 90% penetrance will not be manifested by 10% of persons possessing the gene

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phenotype

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a person's entire physical, biochemical, and physiologic makeup, as determined by the person's genotype and environmental factors

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polymorphism

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a genetic variation with two or more alleles that is maintained in a population

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population screening

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the application of a test or inquiry to a group to determine if persons in the group have an increased likelihood of a genetic condition or a mutation in a specific gene

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predisposition testing

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testing that is used to determine the likelihood that a healthy person with or without a family history of a condition will develop the disorder. Having the gene mutation would indicate that the person has an increased susceptibility to the disorder, but this is not a diagnosis. One example is DNA mutation testing for hereditary breast / ovarian cancer.

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prenatal screening

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testing that is used to identify whether a fetus is a risk for a birth defect such as Down syndrome or spina bifida

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presymptomatic testing

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genetic testing that is used to determine whether persons with a family history of a disorder, but no current symptoms, have the gene mutations. ex. Huntington disease

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recessive

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a genetic trait that is expressed only when a person has two copies of a mutant autosomal gene or a single copy of a mutant X-linked gene in the absence of another X chromosome

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transcription

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the process of transforming information from DNA into new strands of messenger RNA

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trisomy

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the presence of one extra chromosome in an otherwise diploid chromosome complement - for example, trisomy 21 - Down syndrome

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variable expression

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variation in the degree to which a trait is manifested; clinical severity

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X-linked

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located on the X chromosome

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the unit of heredity

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a single gene

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a gene is composed of

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a segment of DNA

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a segment of DNA (gene) contains

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a specific set of instructions for making the protein or preoteins needed by body cels for proper functioning

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genes regulate...

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both the types of proteins made and the rate at which proteins are produced

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components of a DNA nucleotide

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sugar-phosphate molecules
pairs of nitrogenous bases (ACGT)
in a double helix
strands are held together by hydrogen bonds

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female sex chromosomes

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XX

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male sex chromosomes

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XY

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mitiosis is involved in

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cell growth, differentiation, and repair
-all body cells, except sperm and oocytes

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meiosis is involved in

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reproductive cells only, formed the sperm and oocytes

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daughter cells

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the result of mitosis, each contian the same number of chromosomes as the parent cell (diploid)

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recombination

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during the initial phase of meiosis, as the paired chromosomes come together in preparation for cell division, portions cross over, and an exchange of genetic material occurs before the chromosomes separate

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what is the benefit of recombination in meiosis?

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recombination creates greater diversity in the makeup of oocytes and sperm

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nondisjunction during meiosis leads to...

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a sperm or oocyte that contain either two copies (leads to trisomy) or no copies (leads to monosomy) of a particular chromosome

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phenotype of Down syndrome

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trisomy (3 copies of ) chromosome 21

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phenotype of Turner syndrome

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monomy (single copy of X chromosome)
(leads to short stature and infertility)

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inherited aka germlline gene mutation

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present in the DNA of all body cells and are passed on in reproductive cells from parent to child
ex. Huntington disease

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spontaneous mutations

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take place in individual oocytes or sperm at the time of conception
-ex achondroplasia, Marfan syndrome, and neurofibromatosis type 1

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acquired mutations

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take place in somatic cells and involve change in DNA that occur after conception, during a person's lifetime

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cells responses to acquired mutations over a lifetime

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ces have built-in mechanisms by which they can recognize mutations in DNA, and in most situations they correct the changes before they are passed on by cell division. Over time body cells may lose their ability to repair damage from gene mutations, causing an accumulation of genetic changes that may ultimately result in diseases such as cancer and possiby othe conditions of aging, such as Alzheimer's

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single nucleotide polymorphisms (SNPs or "snips")

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the terms used for common genetic variations that occur most frequently throughout the human genome. some SNPs may contribute directly to a trait of disease expression by altering function. ex. affect drug efficacy and safety if it occurs in proteins that are targets of medication regimesn or that are involved in drug transport or drug metabolism

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Mendelian conditions are...

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genetic conditions that are inherited in fixed proportions among generations. they result from gene mutations that are present on one or both chromosomes of a pair

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autosomal dominant

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-affect female and male family member equally
-vertical pattern of inheritance
-each offspring has a 50% chance of inheriting the gene and therefore the disease

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the phenomenon of variable expression results from

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the influences of genetic and environmental factor on clinical presentation

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ex. complete penetrance

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achnodroplasia (100%)

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ex. incomplete penetrance

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BRCA-1 (80%)
otosclerosis (40%)
retinoblastoma (80%)
this person carries the gene mutation and still has a 50% change of passing the gene for the conditionoto each of their children.

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one of the effects of incomplete penetrance is that the gene appears to "skip" a generation

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why? dont understand this??

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autosomal recessive inheritance...

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horizontal pattern - relatives of a single generation tend to have the condition
-frequently seen among particular ethnic groups and more often in children of parents who are related by blood

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ex. autosomal recessive inherited conditions

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Gaucher's disease
cystic fibrosis
sickle cell anemia
PKU
galactosemia
Tay-Sachs
Canavan disease

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ex. x-linked recessive inherited conditions

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Duchenne muscular dystrophy
Hemophilia A and B
Wiscott-Aldrich syndrome
Protan and Deutran forms of color blilndness

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X-linked recessive inheritance

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vertical transmission in families
males predominantly affected

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multifactorial inheritance and complex genetic conditions

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occur as a result of a combination of genetic and environmental factors
may recur in families
inheritance pattern does not demonstrate characteristic pattern of inheritance seen with other mendelian conditions

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multifactorial inherited conditions

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congenital heart defects
cleft lip and/or palate
neural tube defects (anencephaly and spina bifida)
diabetes mellitus
osteoarthritis
high blood pressure

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on a pedigree, which shape is for male and which is for female

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square for male
circle for female

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aneuploidy

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chromosomal differences involving an extra or missing chromosome

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"balanced" chromosomal rearrangements

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have all of their chromosomal material, but it is rearranged
affected women have an increased risk for spontaneous pregnancy loss and for having children with an unbalanced chromosomal arrangement that may result in physical or mental disabilities. should have prenatal counseling and testing

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cytogenetics

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the microscopic study of chromosomes

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fluorescent in situ hybridization _ FISH

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permits detailed examination of chromosomes and detection of small abnormalities

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types of genetic tests

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prenatal testing
carrier testing
newborn screening
diagnostic testing
genetic tests to predict drug response and to design specific and individualized treatment and management plans

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genetic screening

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is a broader concept than genetic testing and applies to testing of populations or groups independent of a positive family history or symptom manifestation

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servire (imperf)

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servivo,-i,-a
servivamo servivate servivano

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multiple endocrine neoplasia - clinical description

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familial medullary thyroid cancer, pheochromocytoma, and parathyroid abnormalities

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multiple endocrine neoplasia - age of onset

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early adulthood; 40-50 years

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multiple endocrine neoplasia - inheritance and risk factors

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autosomal dominant
-carrier or relative of carrier of a RET mutation
-family history of medullary thyroid cancer, pheochromocytoma, and parathyroid abnormalities

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breast cancer - clinical description

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BRCA1 and BRCA2 hereditary breast/ovarian cancer
BRCA1-breast, ovarian, prostate
BRCA2-breast, ovarian, and other

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breast cancer - age of onset

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30-70; often <50

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breast cancer - inheritance and risk factors

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multifactorial - 75%
autosomal dominant 5-10%
mutations in BRCA1 and BRCA2
older age
early menses (<11y)
nulliparity
family history
breast biopsies

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hereditary non-polyposis colorectral cancer (HNPCC) - clinical description

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colorectal, ovarian, endometrial, bladder, gastric, biliary, and renall cell cancers

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hereditary non-polyposis colorectral cancer (HNPCC) - age of onset

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<50

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hereditary non-polyposis colorectral cancer (HNPCC) - inheritance and risk factors

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multifactorial >75%
autosomal dominant - 1-3%
mutation in family of repair genes
older age
personal or family history of colon cancer or adenomas
high-fat, low-fiber diet inflammatory bowel disease

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pharmacogenetics

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the study of the role of genetic variation in drug response and toxicity. involves methods that rapidly identify which genetic variations influence a drug's effect

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4 classes of metabolic variations in pharmacogenetics

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1. poor metabolizers - lack enzyme function - adverse reactions
2. intermediate metabolizers - reduced enzyme activity
3. extenseive metabolizers - normal or expected
4.. ultrarapid metabolizers - increased enzyme activity - poor treatment response

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cytochrome P450 (CYP) family of enzymes

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major involvement in drug metabolism
-3 of them are active in about 40% of CYP-mediated drug responses

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People with genetic variations in the cytochrome P450 enzymes are more likely to..

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experience adverse drug reactions or poor response

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carrier testing offered to ... for....

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sickle cell anemia - African American
Tay-Sachs disease, Canavan disease - Ashkenazi Jewish
cystic fibrosis - all, especially Northern European and Ashkenazi Jewish
BRCA1 - Ashkenazi Jewish

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What is the "therapeutic gap?"

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identification of a genetic susceptibility or diagnosis without an existing cure