Flashcards in Genetics Deck (63)
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Genes
Hereditary units of DNA transmitted from one generation to another; code for proteins
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Locus
The specific location of a gene on a chromosome vs. genetic marker isn’t as exact (zone of a chromosome)
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Alleles
Different versions of a gene; humans have 2 alleles for each autosomal gene
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Chromosomes
Structure composed of genes located in nucleus of a cell
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Homologous chromosomes
Have the same genes at the same loci, one maternal and one paternal
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Genome
The genetic information contained in the cells, on the chromosomes, for a particular species
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Mutation
A change in some part of the DNA code. Can be:
-Spontaneous
-Induced by exposure to mutagenic chemicals or radiation
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Autosome
Any chromosome that is not a sex chromosome (humans have 22 pairs of autosomes)
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Haploid number
the number of chromosomes in sex cells/gametes (n=23)
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Diploid number
the total number of chromosomes in somatic cells (2n=46)
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Somatic chromosomes
Autosomes
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Sex chromosomes
Allosomes
-Males have one morphologically dissimilar pair (heteromorphic), labeled X and Y. Genetic factors on the Y determine maleness
-Females have two morphologically similar X's
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Karyotype
The characterization of the chromosomal complement of an individual or a species, including number, form, and size of the chromosomes.
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Mitosis
-The process by which all somatic cells replicate and become descendants of one original cell
-One exact copy of each chromosome is made and distributed through the division of original cell into two daughter cells
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Meiosis
-The process by which gamete cells are produced (egg and sperm)
-Resulting gametes have 23 new chromosomes, with new combos of the original maternal and paternal copies
-Occurs only in specialized germ cells of gonads
-2 consecutive cell divisions producing cells with half the original chromosome number
--> Diploid 2n-->haploid n
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Genotype
All of the alleles of an organism
-Homozygous: contains the same allele @ a single locus
-Heterozygous: contains 2 different alleles @ a single locus
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Phenotype
a measurable trait an organism has
-i.e. hair color, eye color, blood type
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Dominant allele
Phenotype can be seen in both the heterozygote and homozygote
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Carrier
Heterozygous individual with a recessive alley that's hidden from phenotypic view by the dominant, normal allele
Ex: Cystic Fibrosis
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Recessive allele
Produces this phenotype only when its paired allele is identical
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Single Gene Disorders (Mendelia Disorders) Classification
-Autosomal or x-linked
-Dominant or recessive pattern
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Mendel's Principle of segregation
One parent has 2 copies of a gene for trait, but transmits o only one via a gamete
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Codominance
When two alleles for a trait are equally expressed
Ex: AB blood type
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incomplete dominance
Heterozygotes have phenotypes that have both alleles visible as a blend (makes a third phenotype)
Ex: wavy hair, skin color
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Pentrance
The probability that individuals in a population who have a particular gene combination will show the condition
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Genetic marker
Sequence of DNA with a known location on a chromosome
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Expression
The components of the phenotype that are exhibited in an individual
Ex: Myotonic muscular dystrophy- Two ppl carrying the this gene may express it differently (one has cataracts, the other has grip myotonia)
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Anticipation
Genetic disease that increase in severity or have earlier onset with each successive generation
Ex: Huntingtons dz
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Aneuploidy
Abnormal number of chromosomes
-Most common abnormality
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Balanced chromosomal abnormalities
No net less or gain of chromosomal material, length is still the same
Types:
-Balanced translocation
-Inversion
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Balanced translocation
Rupture of a chromosome resulting in the pieces "re-sticking" in the wrong combinations
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Inversion
A chromosome piece is lifted out, turned around, and reinserted
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Unbalanced chromosomal abnormalities
Additional or missing information
-Deletion
-Insertion (can be beneficial or lethal)
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Unbalanced translocation
Tends to arise as an offspring of a balanced carrier
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Robertsonian translocation
-involve 2 out of chromosomes 13, 14, 15, 21, and 22
-All acrocentric
-The bigger chromosome can produce an unbalanced gamete
-Chromosome 21= Down syndrome
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What are the functions of a three-generation pedigree?
-Making a diagnosis
-Deciding on testing strategies
-Establishing the pattern of inheritance
-Identifying people at risk
-Educating the patient
-Determining reproductive options
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Consultand
-The person seeking genetic advice
-Represented by an arrow on pedigree
-Can be healthy or a person with a condition
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Proband
The affects individual
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Characteristics of Autosomal Dominant (6)
1. Vertical pattern- Transmission passes from parent to offspring
2. Multiple generations affected
3. Variable expressivity- Affected individuals in same family may show varying degrees of phenotypic expression (severity)
4. Reduced Penetrance-Some with the genetic mutation may not show phenotype, making it appear that it "skipped" a generation
5. Males and females affected equally
6. Male-to-Male transmission can be seen
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Autosomal Dominant
-65% of human monogenic disorders
-Mutations in a single allele can cause dz
-Affected individuals are HH or Hh
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Autosomal Recessive
-25% of human monogenic disorders
-Two copies of diseased allele required for expressing the phenotype
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Characteristics of autosomal recessive (5)
1. Horizontal inheritance-multiple affected offspring
2. Higher associated with consanguinity- closer relatives having children with each other
3. Males and females affected equally
4. Inheritance is from both parents, each being heterozygote/carrier
5. Each offspring has a 25% chance of being affected and a 50% chance of being a carrier
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X-linked
-5% of human monogenic disorders
-Males are hemizygoes (heterozygous) for mutant allele the x
-->only have one x and don't have another x to overshadow it or cover it
-No male to male transmission is possible: Dad only gives his Y to his son (no x)
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Multifactorial/Complex Disease
-Caused by interactions of variations in multiple genes and environmental factors
-Identified for complex conditions such as: Cancer, DM, asthma, heart dz, mental illness, cleft lip/cleft palate
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Down syndrome
-Trisomy 21 (95%)
-Most common non-lethal trisomy
- 4% Roberstonian translocation
-Prenatal Testing: Quad screen & nuchal translucency (thickness of the skin
-Intellectual disability
-cardiac/GI defects, hearing loss, visual problem
-increased risk for alzheimer dz (half of adults)
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Trisomy 18
-Edwards Syndrome
-2nd most common autosomal trisomy (after 21)
-Club foot (Rocker bottom feet)
-Low set ears, small jaw, development delay, kidney/GI/heart defects
-IUGR: Intrauterine growth restriction (retardation)
-High mortality rate
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Trisomy 13
-Patau Snydrome
-Cleft lip/palate, polydactyly
-High mortality rate
-Most cases=3 copies of chromosome 13
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Cri-du-Chat Syndrome
-Deletion of PART of short arm of chromosome 5
-Partial monosomy (when only a portion of a chromosome has one copy instead of two)
-Cat-like-Cry from abnormal larynx development
-Intellectual disability, wide set eyes, low ears
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Klinefelter's Syndrome
-47XXY
-Occurs during gametogenesis
-Most common sex chromosome aneuploidy in males
-Affects male physical and cognitive development (becomes more apparent after puberty): Hypogonadism, Gynecomastia (development of breast), reduced body hair
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Turner syndrome
-45X: Affects development in female
-Gonadal Dysgenesis (non-functional ovaries)
-Short stature, broad chest, webbed neck
-Amenorrhea, infertility
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Huntington's Disease
-Neurodegenerative Dz: Progressive brain disorder
-HD Gene on chromosome 4 that codes for "Huntington" protein
-CAG Trinucleotide Repeat (36-120 repeats)
-Most cases are inherited: Autosomal dominant
-Genetic anticipation
-Early signs: Depression, irritability,
-Adult onset: genetic defect is latent for 3-5 decades
-Causes Chorea (involuntary jerking movements)
-ONLY human disorder of complete dominance
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Alzheimers Disease
-Neurodegenerative dz
-Formation of plaques and tangles
-Most common form of dementia in older individuals
-Two forms of AZ dz:
1. Sporadic AZ (late onset)= Most cases, after age 65, chromosome 19 APOE gene increases risk
2. Familial AZ (early onset)= Rare, before age 65, autosomal dominant
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Hereditary Breast and Ovarian Cancer
Two major cancer susceptibility genes:
1. BRCA1- Chromosome 17
2. BRCA2- Chromosome 13
-Mutated gene increases risk
-Autosomal dominant
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Colorectal Cancer
-Diet, smoking and obesity increase risk more than genetics
Types of colorectal cancer:
1. Familial
-May be due to chance alone
-Shared exposure to a carcinogen or diet/lifestyle
-Combo of gene mutations/environment
2. Hereditary
-->Familial Adenomatous Polyposis (FAP)=less than 1%
-Hundred/thousands of polyps
-Autosomal dominant
-APC gene on chromosome 5
-Develops in 20's
-100% risk of developing CA before age 50
-->Nonpolyposis Colorectal Cancer (HNPCC)=Lynch Syndrome
-2-3% of all colorectal cancers
-Autosomal dominant
-Small number or no polyps
-50% chance in Women
-70% chance in Men
-Regular colonoscopy starting @ age 25 for relatives or beginning 5 years younger than affected family member
-Associated with formation of other cancers
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Chronic Myelogenous Leukemia
-Myeloproliferative disorder
-More common in men (55 yrs)
-Translocation between chromosome 9-22
-Philadelphia chromosome 22
=Causes body to make too many WBC's (non-functional)- Takes up bone marrow space for healthy WBC's
-Fever, night sweats, fatigue
-Slow onset, progressive
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Hemophilia
-Mutation on F8/F9 gene o x chromosome
-Males mainly affected
-Hemophilia A: F8 Gene= Most common
-Hemophilia B: F9 Gene= Christmas disease
-Hemarthrosis (popcorn)
=spontaneous bleeding into a joint
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Sickle Cell Disease
-Mutation on HBB gene
-Autosomal RECESSIVE
-Atypical Hemoglobin molecules=Crescent shaped break down prematurely
-Anemia, infections, SOB, fatigue
-Common in specific areas
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Cystic Fibrosis
-Autosomal RECESSIVE
-Mutation in the CFTR gene that codes for chloride channels in epithelial cells
-Water balance in secretions is disrupted= Thick, sticky mucus obstructing in airways in lungs and ducts of pancreas
-Failure to thrive, poor growth
-Meconium ileum (popcorn)
-->newborn intestinal obstruction due to thick fecal waste products
-Pulmonary dz= Most common cause of morbidity
-->pulmonary systems can't defend against pathogens well
-->Chronic sinus infections common in CF pt's (this isn't normal in kids)
-Sweat Chloride test
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Marfan Syndrome
-Autosomal dominant
-Mutation on FBN1
-Defects in connective tissue (hyper flexible joints)
-Tall, long arms, arm span>height
-Dislocated lens of eye (popcorn)
-Aoritic aneurysm/dissection (popcorn)
-Advised to avoid sports, caffeine, decongestion to avoid increased stress on CV system
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Neurofibromatosis Type 1
-Autosomal Dominant
-NF1 gene on chromosome 17=tumor suppressor gene
-Growth of neurofibromas on nerves of skin and brain
-Cafe-au-lait spots=Hyperpigmented skin
-Crowe sign= axillary/inguinal feckling
-Lisch nodule in eye
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Polcystic Kidney Disease
-Fluid filled sacs in kidneys
-Can't filter blood properly
-->Kidneys enlarge and can fail
-HTN, back pain, hematuria, UTI's, kidney stones
-Increased risk of aortic/brain aneurysm
-Two forms:
1. Autosmal Dominant= more common, develop in adulthood
2. Autosmal Recessive= RARE, lethal early in life
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Teratology
Study of abnormal development
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