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Patho Exam 4 > park-genetic diseases > Flashcards

park-genetic diseases Flashcards

1
Q

How many pairs of chromosomes are there?

A

23 pairs (46 chromosomes total)
-a pair has two homologous chromosomes (one from each parent)

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2
Q

How many pairs are autosomal?

A

22 (44 chromosomes total)

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3
Q

How many pairs are sex chromomes?

A

1 pair (2 chromosomes total)
-XX is female
-XY is male
-Y chromosomes only has ~100 genes (significantly less than X )

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4
Q

What is X-inactivation (lyonization)

A

-one X chromosome is inactivated in female cells
-it is randomly decided within a few days of conception
-normal women have 50% maternal and 50% paternal active X chromoso,es

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5
Q

Genotype

A

genetic information stored in the DNA sequence

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6
Q

phenotype

A

-recognizable traits, physical or biochemical, that are associated with a specific genotype
-more than one genotype may have the same phenotype

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7
Q

Gene

A

-a segment of DNA sequence that contains genetic information to express proteins or RNA
-the functional unit of inheritance

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8
Q

Allele

A

-each copy of a gene in a pair of a chromosome
-human genes have two alleles, one in each chromosomes (except genes in tY chromsome)

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9
Q

Mendels law of inheritance

A

-each parent passes down one allele for each gene to their offspring (segregation)
-some alleles are dominant over others, and that organism will display the dominant trait if they inherit at least one dominant allele (dominance)
-the inheritance of one pair of genes is independent of the inheritance of another pair (independent assortment)

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10
Q

monogenic traits

A

-also called single-gene traits
-follows mendels law
-only one pair of genes is involved
-dimple, widow’s peake, etc

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11
Q

polygenic traits

A

-many genes are involved
-traits have gaussian distributions
-contribution of each gene to the traits may vary
-height, skin color, etc

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12
Q

multifactorial inheritance

A

-many genes and environmental effects are involved

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13
Q

How do variants occur?

A

-inherited (hereditary
-non-inherited
-new (de novo) variants

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14
Q

Inherited variant

A

-passed from parent to child
-present throughout a person’s life in virtually every cell in the body
-present in the parent’s egg or sperm (germ cells)

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15
Q

Non inherited variants

A

-occur at some time during a persons life
-not every cell in the body
-somatic variations
-not passed to next generation
-can be caused by environmental factors (eg. UV) or result from an error in DNA replication

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16
Q

New (de novo) variants

A

-found in child but not either parent (no family history of disorder)
-may pass the variant to his or her children
-may occur in parents egg or sperm but not present in any other cells (somatic)
-in the fertilized egg shortly after the egg and sperm unite
-variants acquired during development can lead to mosaicism (cells within the same person have different genetic makeup)

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17
Q

What are types of genetic variants?

A

-substitutions
-insertions and deletions
-mutations in non-coding region

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18
Q

what are types of substitution variants

A

-silent mutation
-missense mutation
-nonsense mutation

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19
Q

silent mutation

A

no change in the amino acid sequence

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20
Q

missense mutation

A

change in the amino acid sequence

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21
Q

nonsense mutation

A

addition of a stop codon

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22
Q

insertion and deletion

A
  • a multiple of three basses-insertions or deletions of one or more amino acids
    -not a multiple of three bases - frameshift
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23
Q

where can mutations in non-coding regions occur?

A

-enhancer, repressor, or promoter regions
- 5’ UTR, introns, or polyadenylation signal

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24
Q

what does a mutation in the enhancer, repressor, or promoter region lead to?

A

change in gene expression levels

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25
Q

what does a mutation in the 5’ UTR, introns, or polyadenylation signal lead to?

A

defective RNA splicing or mRNA maturation

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26
Q

What effects can mutations have on gene activity?

A
  • no effect
    -complete loss of function
    -partial loss of function
    -gain of function
    -dominant negative
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27
Q

no effect mutaions

A

-no change in the amino acid sequence (silent mutation)
-mutated protein with the same activity as the unmutated protein

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28
Q

complete loss of function mutation

A

-no expression
-mutated protein with no activity

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29
Q

partial loss of function mutation

A

-reduced expression
-mutated proteins with reduced acitivity

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30
Q

gain of function mutation

A

-mutated proteins with abnormal activity (oncogenes)

31
Q

dominant negative mutation

A

-inhibition of the activity of the unmutated protein expressed from the normal allele

32
Q

In the event of a complete loss of function gene___

A

-dominant/ more than 50% of gene function is needed for normal or pathological function (DD= normal, Dd and dd = patholgical/haplosufficiency)
-recessive/ less than 50% is normal (DD and Dd) or pathological (dd)

33
Q

Single gene locations occur due to?

A

-a defective or mutant allele at a single gene locus
-follows mendelian pattern of inheritance

34
Q

what does the pattern of inheritance depend on in single gene disorders?

A

-whether the phenotype is dominant or recessive
-whether the gene of concern is located on an autosomal or sex chromosome

35
Q

what are the different types of single gene disorders?

A

-autosomal dominant
-autosomal recessive
-X linked dominant
-X linked recessive

36
Q

What do most single gene disorders lead to?

A

virtually all disorders lead to the formation of
-an abnormal protein
or
-decreased production of a gene product

37
Q

Autosomal dominant

A

-50% chance of passing the trait to each child
-some probability for males and female children
-unaffected relatives or siblings DO NOT transmit the disorder
-in many cases the age of onset is delayed
-Huntington disease or Marfan syndrome

38
Q

Autosomal recessive disorder

A

-if both parents are carriers then 25%:50%;25% chance of having an noncarrier (DD), carrier (Dd), and affected (dd) child
-same probability for males and female children
-unaffected siblings may be carriers
-all children of an affected parent are carriers
-age of onset is frequently early in life for many conditons
-symptoms tend to be more uniform than with autosomal dominant
-phenylketonuria, Tay-sachs disease are all inborn errors of metabolis

39
Q

Penetrance

A

-the percentage of individuals with a particular genotype (or gene mutation) who express the associated phenotype (or symptoms of a disorder)
- complete penetrance = 100%
-incomplete penetrance= < 100% (reduced penetrance)
-influenced by genetics, environment, and lifestyle factors

40
Q

Expressivity

A

-the degree to which a genotype (or gene mutation) is expressed as a phenotype (or symptoms of a disorder) with an individual with the genotype
-some may have relatively mild symptoms of a conditions while others symptoms are debilitating (variable expressivity)
-influenced by other genes, epigenetic, environmental factors

41
Q

What is an example of autosomal dominant disease?

A

-osteogenesis imperfecta type 1 (brittle bone disease)
-caused by mutations in the genes for collagen
-all individuals with the mutation show symptoms (complete penetrance)
-affected individuals exhibit varied severity (variable expressivity)

42
Q

X liked genetic disorders

A

-generally men are affected and women are carriers because men only have one X while women have two Xs
-EX: in case that the frequency of the mutated allele in a population is 1/1000
–only 0.1% of men are affected
–only 0.0001% of women are affected
-0.1% of women are carriers

43
Q

X linked recessive disorders

A

-female heterozygotes (Xx) are unaffected (carriers)
-all males who receive the gene (xY) are affected
-if mother is a carrier 50% of daughters are normal and 50% are carriers
-if mother is a carrier 50% of sons are normal and 50% are affected
-if father is affected 100% of daughters are carriers
-if father is affected 100% of sons are normal
-color blindness and hemophilia A

44
Q

X linked dominant disorders

A

-frequently embryonic lethal for males (xY) and for homozygous mutant females (xx)
-in the case that mother is affected (Xx) both sons and daughters have a 50% chance to be affected
-in the case that father is affected (xY) daughters are 100% affected (Xx) and sons are 100% normal
-fragile X syndrome

45
Q

inherited multifactorial disorders

A

-caused by the influence of multiple genes along with environmental factors
-environmental factors have greater role in disorders that develop in adults ( coronary artery disease, diabetes mellitus, hypertension, cancer,etc)
-cannot be predicted as accurately
-when parents have a baby with a multifactorial congenital malforation, the risk of recurrence in future pregnancies is high for the same or a similar defect
-the first degree relatives of an affected person have an increased risk
-the risk increases with increasing numbers of incidence of the defect among relatives
-cleft lip, club foot,

46
Q

mitochondria

A

-contains own DNA (mtDNA)
-a circular chromosome with 37 genes (similar to bacteria)

47
Q

mitochondrial gene disorders

A

-inherited from the mother only
-cells contain many mitochondria (100-1000), which may a mixture of normal and mutant DNA (heteroplasmy)
-the severity of the disorder depends on the proportion of the mitochondria that carry the mutated gene
-affected organs that depend most on oxidative phosphorylation (skeletal muscle, heart, brain)
-encephalopathies, myopathies, deafness, muscle weakness

48
Q

chromosomal disorders

A

-affects 1 in 200 newborns

49
Q

what are the types of chromosomal disorders?

A

-abnormal number of chromosomes (aneuploidy)
-alterations to the structure of one or more chromosomes

50
Q

karyotype

A

appearance of the complete set of an individual, mainly including their sizes, numbers, and shape

51
Q

How are chromosomal disorders described?

A

-shorthand description is frequently used
-total number of chromosomes, sex chromosome, and any abnormality
- 46, XX= normal female
-47, XY, +21 = male with down syndrome (trisomy 21)

52
Q

What is an abnormal number of chromosomes (aneuploidy)?

A

-having less or more than 46 chromosomes
-occurs due to unbalanced segregation of chromosomes during meiosis (nondisjunction)
-nondisjunction produces germ cells with 22 or 24 chromosomes (one less or one more)

53
Q

Fertilization of gametes with aneuploidy

A

-defects associated with monosomy of the autosome are severe and often cause miscarriage in utero
-in contrast to down syndrome (trisomy 21) other trisomies (13/ 18) are more serve and rarely survive past the first year

54
Q

mosaicism abnormal chromosome numbers

A

-caused by nondisjunction occurring in the early stage of development
-part of the cells in the body have abnormal number of chromosomes
-relatively mild symptoms compared with full trisomy/monosomy

55
Q

what types of testing can be done for abnormal number of chromosomes?

A

-amniocentesis
-prenatal cell-free DNA (cfDNA) screening

56
Q

Down syndrome

A

-trisomy 21in 95% of cases
-most common chromosomal disorder
-intellectual disability
-characteristic facial features

57
Q

Turner syndrom

A

-monosomy X (45 X/0)
-short in stature
-no signs of secondary sex characteristics
-no menstruation

58
Q

Klinefelter syndrome

A
  • 47, XXY or 48 XXXY
    -male with testicular dysgenesis
    -deficient secondary sex characteristics
    -phenotype is variable
    -many live without knowing the abnormality
59
Q

abnormal structures of chromosome

A

-deletion, translocation, inversion, ring formations may occur
-caused by breakage in the chromosome during meiosis
-exposure to radition, chemicals, or viral infection can trigger
-with a balanced reciprocal translocation or inversion, no genetic information is lost (person with alterations are usually normal)

60
Q

Disorders involving genomic imprinting

A

-some regions of DNA are turned off in the copy received from mother or father (genomic imprinting)
-epigenetic process that involves DNA methylation and histone modification
-about 200 imprinted genes are known in human: only one copy of the genes (paternal or maternal) is functional
-imprinting occurs in gametes and is then stably transmitted to all somatic cells derived from the zygote (fertilized egg)
-if a gene is turned off in the maternal copy and mutated in the paternal copy, none of the copies with produced a functional protein

61
Q

Prader willi syndrome and angelman syndrome both___

A

have similar region of chromosome 15 that is deleted

62
Q

Prader-willi syndrome

A

-deletion is inherited from the father
-genes from mother are silenced through imprinting
-mental retardation, ataxic gait, seizure

63
Q

Angelman syndrome

A

-deletion inherited from mother
-gene from father is silenced through imprinting
-mental retardation, short stature, obesity, hypogonadism

64
Q

Which of the following statements about human chromosomes is correct?
A. human cells have 23 chromosomes
B. homologous chromosomes have different chromosome numbers
C. the two copies of genes in homologous chromosomes always have identical DNA sequences
D. the paternal X chromosome is inactivated in female cells
E. Y chromosome has much smaller number of genes than X chromosome

A

E. Y chromosome has much smaller number of genes than X chromosome

65
Q

Which of the following statements is correct regarding genetic variants?
A. a silent mutation suppresses the expression of a protein
B. a missense mutation adds a single amino acid residue to the amino acid sequence of a protein
C. a nonsense mutation adds a string of amino acid residues to the end of a protein
D. mutations in non-coding regions are all silent mutations
E. deletion of a single nucleotide causes a frameshift which adds wrong amino acids to a protein

A

E. deletion of a single nucleotide causes a frameshift which adds wrong amino acids to a protein

66
Q

A loss-of-function mutation can be dominant or recessive based on___
A. whether the gene is located on an autosome or sex chromosome
B. whether the remaining protein activity is sufficient for the normal function of the cell or not
C. what type of substitution is caused by the mutation
D. whether the mutation is located in a protein coding or noncoding region
E. whether the mutation is silent or not

A

B. whether the remaining protein activity is sufficient for the normal function of the cell or not

67
Q

Widows peak is an autosomal dominant genetic trait. If both parents do nor have widows peak, what is the chance that their children have widow’s peak?
A. 0%
B. 25%
C. 50%
D. 75%
E. 100%

A

A. 0%

68
Q

AD, 17 year old male, visited his doctor for systemic muscle weakness and wasting. The doctor discovered that AD had a rare genetic disorder called charcot-marie-tooth disease. Surveying his pedigree, the doctor did not find anyone with the disease. Also his parents do no have the mutation. Which of the following is not a possible explanation for AD’s disease?
A. a de novo mutation occurred in the fathers sperm
B. a de novo mutation occurred in the mothers egg
C. a de novo mutation occurred in one of his muscle cells recently
D. AD is adopted
E. ADs mother has cheated

A

C. a de novo mutation occurred in one of his muscle

69
Q

The following diagram shows the pedigree of a single-gene disorder. Carriers are shown in dark blue, the affected individuals are shown in light blue. Women are shown as circles, and men are shown as squares. What is the type of this genetic disorder?
A. autosomal dominant
B. autosomal recessive
C. X linked dominant
D. X linked recessive

A

D. X linked recessive

70
Q

Only a small fraction of women with mutations in BRCA1 gene develop cancers. What can we learn from this observation?
A. The BRCA1 mutations have complete penetrance
B. The BRCA1 mutations have incomplete penetrance
C. The BRCA1 mutations have consistent expressivity
D. The BRCA1 mutations have variable expressivity

A

B. The BRCA1 mutations have incomplete penetrance

71
Q

Which of the following genetic disorders is causes by one or two extra X chromosomes i men?
A. down syndrome
B. turner syndrome
C. kleinfelter syndrome
D. prader-willi syndrome
E. Angelman syndrome

A

C. kleinfelter syndrome

72
Q

Leigh syndrome is a genetic disorder affected central nervous system. About 20% of the patients with Leigh syndrome has mutations in MT-ATP6, a mitochondrial gene necessary to produce functional ATP synthase. Which of the following statements is correct about the Leigh syndrome caused by the mutations of MT-ATP6?
A. Only men are affected
B. only women are affected
C. when mother is affected, all of her children are affected
D. when father is affected, all of his children are affected
E. An affected child always has both affected father and affected mother

A

C. when mother is affected, all of her children are affected

73
Q

Genomic imprinting refers to___
A. inactivation of either the maternal or paternal copy of a gene
B. a mutation with complete penetrance
C. a permanent change to the genomic DNA sequence
D. creation of a new disease-causing mutation during development
E. a balanced chromosomal alteration

A

A. inactivation of either the maternal or paternal copy of a gene

Patho Exam 4 (6 decks)

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