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Basic Pathology > Genetics > Flashcards

Genetics Flashcards

1
Q

DNA:

  • information storage material for ____
  • structure: ____
  • 4 paired nucleotide bases: _____
A

all organisms and many viruses;
double-stranded helix;
adenine-thymine, gaunine-cytosine

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2
Q

codon

A

triplet of DNA bases that code for a specific amino acid

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3
Q

amino acids are assembled into ____

A

proteins

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4
Q

proteins are the foundation for ____

A

all cellular structure and function

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5
Q

gene

A
  • DNA sequence that codes for a protein

- basic operational unit of genetic information

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6
Q

____ genes in human genome

A

~50,000

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7
Q

_____% of DNA is used for making proteins:

  • ____% is regulatory only
  • ____% is the actual code for the protein
A

10;
8;
2

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8
Q

DNA is transcribed into _____ in the _____

A

RNA;

nucleus

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9
Q

RAN is translated into _____ in the _____

A

protein;

cytoplasm

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10
Q

exons

A

portions of gene translated into protein

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11
Q

intron

A
  • portions of gene removed from RNA transcript before translation
  • non-coding parts
  • no translation to protein (RNA splicing)
  • regulation of expression of genes
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12
Q

factors effecting transcription

A
  • external or internal: cytokines/toxins/medicine

- can elicit or inhibit RNA transcription

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13
Q

epigenetics

A
  • extra-DNA modifications to the genome
  • chemical compounds that regulate DNA expression (e.g., methylation silences transcription)
  • influence phenotype
  • do not change the DNA sequence
  • not encoded by the DNA sequence
  • can be inherited and/or acquired by external factors (diet, pollutants, etc.)
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14
Q

epigenetics:

  • fetal changes are ____
  • environmental changes are _____
  • preconception exposure of gametes affects _____
A

permanent;
temporary;
gene expression

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15
Q

genome

A

total collection of genetic information

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16
Q

chromosomes

A
  • super-coiled storage structure for genes

- 46 chromosomes/23 pairs

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17
Q

diploid

A

2 copies of each chromosome

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18
Q

haploid

A

1 copy of each chromosome (gametes)

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19
Q

autosome

A

homologous pairs (chromosomes 1-22)

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20
Q

allosome

A

sex chromosomes (X and Y)

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21
Q

locus

A
  • location of a gene/marker on the chromosome

- diploid cells have 2 loci per gene (one per chromosome)

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22
Q

allele

A

gene variant at a particular locus

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23
Q

homozygous

A

both alleles are the same

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24
Q

heterozygous

A

both alleles are different

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25
Q

genotype

A

“the code”; 2 alleles at the same locus

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26
Q

phenotype

A

“shine through”; expression of the code (ex: hair color, height, eye color, presence or absence of a disease)

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27
Q

penetrance

A

likelihood of manifesting a particular phenotype given the same genotype

28
Q

complete penetrance

A

everyone with the same genotype manifests the same phenotype

29
Q

incomplete penetrance

A

everyone has the same genotype, but some do not manifest the same phenotypes

30
Q

expressivity

A

degree to which the phenotype is expressed

31
Q

variable expressivity

A

degree of phenotype expression varies between individuals with the same genotype

32
Q

penetrance and expressivity can both be affected by _____

A

lifestyle/environmental factors

33
Q

Mendelian inheritance:

6 general patterns of inheritance

A
  • co-dominant
  • autosomal dominant
  • autosomal recessive
  • X-linked dominant
  • X-linked recessive
  • mitochondrial
34
Q

Autosomal Dominant Disorders:

  • affected males and females appear in ____ generation of the pedigree
  • affected mothers and fathers can transmit the phenotype to _____
A

each;

both sons and daughters

35
Q

Autosomal Dominant Disorders:

ocular examples

A
  • Retinitis Pigmentosa: progressive vision loss

- Dominant Optic Atrophy: progressive vision loss

36
Q

Retinoblastoma

A
  • autosomal dominant disorder with “reduced penetrance”
  • 90% of patients who inherit this gene will develop the condition
  • Rb1 gene mutation
  • usually unilateral
37
Q

Autosomal Recessive Disorders:

  • almost always associated with _____ of the affected gene
  • both parents must be _____ to transmit the disorders
  • disease appears _____ in male and female children of unaffected parents
A

the loss of function;
at least heterozygous;
equally

38
Q

Autosomal Recessive Disorders:

systemic examples

A
  • cystic fibrosis

- sickle cell disease

39
Q

Sickle Cell Disease

A
  • point mutation on chromosome 11
  • “mis-sense” mutation changes amino acid sequence
  • alters protein structure to hemoglobin-S
  • HB-S (not bound) aggregates –> semisolid gel –> vascular occlusion
  • lowered levels of oxygen cause “crises”
  • cells sickle and become sticky, blocking blood flow
  • clot formation all throughout body
40
Q

Sickle Cell Disease epidemiology

A
  • 9% of African Americans have “sickle cell trait” (heterozygous)
  • 1 in 600 African Americans have sickle cell anemia (homozygous)
41
Q

Sickle Cell Disease ocular manifestations

A
  • ischemia causes retinopathy
  • “sea fan” neovascularization
  • vitreous hemorrhages
  • retinal detachments
42
Q

Autosomal Recessive Disorders:

ocular examples

A
  • Retinitis pigmentosa

- Congenital stationary night blindness (rod dysfunction)

43
Q

Co-dominant Inheritance:

  • one gene has more than one allele that can ____
  • each allele makes ____
  • phenotype is influenced _____
  • ex: ____
A

be expressed simultaneously;
a slightly different protein;
by both alleles;
ABO locus (i.e., blood type)

44
Q

X-Linked Dominant Disorders:

  • affected males pass the disorder ____
  • affected heterozygous females mating with unaffected males pass the condition to _____
A

to all daughters but to none of their sons;

half their sons and daughters

45
Q

X-Linked Dominant Disorders:

systemic example

A

Fragile-X syndrome

46
Q

X-Linked Dominant Disorders:

ocular example

A

ocular alibinism

47
Q

Fragile X-Syndrome

A
  • tri-nucleotide repeat disorder
  • variable penetrance
  • variable expression (males > females)
  • clinical findings: intellectual disability, physical changes (long face, large ears, hypotonia)
  • ocular manifestations: strabismus and refractive errors
48
Q

X-Linked Recessive Disorders

  • affect more ____
  • asymptomatic female carriers transmit the disorder to ____
  • examples: _____
A

males than females;
50% of their male offspring;
hemophilia, red-green colorblindness, retinitis pigmentosa

49
Q

X-Linked Ocular Disorders

A
  • red-green color blindness
  • blue cone monochromat
  • congenital stationary night blindness
  • retinitis pigmentosa (can also be autosomal dominant and others)
  • choroideremia: nyctalopia (progressive degeneration of choriocapillaris which will cause progressive vision loss)
50
Q

Mitochondrial Inheritance Disorders:

  • applies to genes ____
  • only passed by ____
  • disorder appears in ____ generation of a family
  • males __ females
  • example: ____
A 
in mitochondrial DNA;
mother;
every;
=;
Leber's Hereditary Optic Neuropathy
51
Q

Leber’s Optic Neuropathy

A
  • point mutation of mitochondrial DNA causing apoptosis of retinal ganglion cells (RGC)
  • symptoms: bilateral acuity loss, dyschromatopisa, onset typically in early 20s
  • expressivity and penetrance vary between sexes (males>females)
52
Q

chromosomal disorders:

  • reflect events that occur at _____
  • occur from: ____
A

the time of meiosis as gametes are being formed;
nondisjunction (defective movement of an entire chromosome), breakage of a chromosome with loss or translocation of genetic material (translocation, deletion)

53
Q

nondisjunction

A
  • unequal separation of chromosomes during meiosis (chromosomal disorders) or mitosis (mosaicism)
  • homologous chromosomes or sister chromatids do not separate properly (meiosis I or II)
  • will have either two copies of a chromosome or no copies
  • unification with normal haploid cells= trisomy or monosomy
  • results in 22 or 24 chromosomes in the egg or sperm
54
Q

trisomies

A
  • 3 copies rather than 2 copies of a chromosome

- trisomy 21 is most common form (Down Syndrome)

55
Q

monosomies

A

-1 copy rather than 2

56
Q

Trisomy 21/Down Syndrome

A
  • variable expressivity
  • signs and symptoms: intellectual disability, simian crease, umbilical hernia, leukemia
  • ocular manifestations: epicanthic folds, brushfield spots, refractive error, cataracts (early onset)
57
Q

Klinefelter’s syndrome

A
  • nondisjunction of #23 (47, XXY karyotype)
  • phenotypically male
  • signs and symptoms: learning disabilities, hypogonadism, female secondary sex characteristics at puberty (persistent gynecomastia, female hair distribution)
  • one Barr body
58
Q

Turner Syndrome

A
  • most common monosomy
  • nondisjunction of #23 (45, X karyotype)
  • phenotypically female
  • signs and symptoms: short stature, shield chest, webbed neck, reproductively sterile, heart and kidney defects
  • ocular manifestations: many binocular vision problems
59
Q

chromosomal translocation

A

-transfer of chromosome parts between nonhomologous chromosomes

60
Q

balanced translocation

A
  • equal pieces of chromosomes exchanged

- fragments remain functional

61
Q

Robertsonian translocation

A
  • “unbalanced”

- additional cause of Down Syndrome

62
Q

chromosomal deletion

A
  • loss of a portion of a chromosome
  • intermediate deletions lead to disorders
  • Cri du chat syndrome
  • Eye: WAGR syndrome (chromsome 11, wilms tumor/aniridia/genital and mental dysfunction), Retinoblastoma (chromosome 13)
63
Q

Cri-du-chat syndrome

A
  • loss of the short arm of chromosome 5
  • clinical findings: intellectual disability, cat-like cry, ventricular septal defect
  • ocular manifestations: hypertelorism (broadly spaced eyes), epicanthal folds, down-slanting palpebral fissures, strabismus
64
Q

mosaicism

A
  • occurs during early mitosis
  • two genetically different cell lines derived from a single fertilized egg
  • due to: nondisjunction, point mutations
  • ex: heterochromia
65
Q

polygenic/multigenic disorders

A
  • disease incidence is affected by multiple genes in addition to lifestyle and environmental factors
  • examples: diabetes, heart disease, autoimmune disease, cancer, mental illness, refractive error, macular degeneration

Basic Pathology (21 decks)

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