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aude 5310 - embryology > Lectures 7 and 8 > Flashcards

Lectures 7 and 8 Flashcards

1
Q

What was the human genome project?

A

1990 to 2003
18 countries participating
Primary goals were to discover the complete set of human genes, to make the information accessible for further biological study, and to determine the complete sequence of DNA bases in the human genome

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2
Q

What is a pedigree?

A

A pedigree is a specialized chart or family tree that uses a particular set of standardized symbols

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3
Q

How are individuals in a pedigree identified?

A

By a set of 2 numbers
Roman numerals (I, II, III…) symbolize generations
Arabic numerals (1, 2, 3…) symbolize birth order within each generation

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4
Q

Can names also be used to identify someone in a pedigree?

A

Yes

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5
Q

What is the objective of a pedigree?

A

To show and analyze the history of inherited traits through generations in a family

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6
Q

Are pedigrees helpful in following and diagnosing heritable traits?

A

Yes
They do this by describing patterns or modes of inheritance

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7
Q

Can pedigrees prove a certain mode of inheritance every time?

A

No, more often they are ruling out certain modes

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8
Q

What does mode of inheritance mean?

A

Dominant, recessive, etc.

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9
Q

What information must be included on a pedigree?

A

Proband
Race/ethnicity
First name or initials of relatives
Alternatively, generation-individual numbers (I-1, I-2, II-1) can be used to maintain confidentiality (HIPAA)
Affected status (person with the trait/disease) for each individual in the pedigree
Age of all family members, or age at death
If individual deceased, then cause of death, if known, is indicated below the person’s symbol
Adoption status
Pregnancy/abortion
Consanguinity (mating within close relatives)
Marriage/divorce
Date pedigree obtained
Key to shading of symbols

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10
Q

What is a proband?

A

The person we want to know about/study

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11
Q

Where do male partners usually go on a pedigree?

A

To the left, and the female goes to the right

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12
Q

Where does the oldest sibling go on a pedigree?

A

Oldest on the left, youngest on the right
Siblings are connected by
a horizontal line above the symbols

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13
Q

How do you denote year of birth on a pedigree?

A

b. date

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14
Q

How do you denote year or age at death?

A

d. date/82 y

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15
Q

How do you denote a pregnancy on a pedigree?

A

Diamond with a P if sex is unspecified
Square (male) or circle (female) with P if gender is known
Gestational age written below the diamond/symbol

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16
Q

How do you denote if someone is alive and well?

A

A.W.

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17
Q

How is mating denoted in a pedigree?

A

Connected by a straight horizontal line

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18
Q

How is consanguinity (same ancestor) denoted on a pedigree?

A

Double horizontal line connecting them

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19
Q

What are the different degrees of consanguinity?

A

First degree = parents
Second degree = siblings
Third degree = first cousins/aunts and uncles

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20
Q

Are we looking at social relationships in a pedigree?

A

No, just genetic ones

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21
Q

What are monozygotic twins?

A

Twins that develop from a single fertilized egg, i.e., identical twins of the same gender
Occurs b/c of the splitting of the zygote at any stage of development, even as early as the two-cell stage
Both zygotes implant separately, and each has its own placenta and chorionic (gestational) sac

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22
Q

What are dizygotic twins?

A

Develop from simultaneous shedding of two ooctyes, and their subsequent fertilization by two different sperms, i.e., fraternal twins of different genders
The individual twin off-springs are no more similar than siblings

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23
Q

What is a locus?

A

Specific location of a gene or DNA sequence on a chromosome

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24
Q

What is homozygous?

A

Carrying identical alleles for one or more genes

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25
Q

What is heterozygous?

A

Carrying two different alleles for one or more genes

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26
Q

What is heterogeneity?

A

Many genes with one phenotype

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27
Q

What are some examples of heterogeneity?

A

Deafness/hearing loss
Blood clotting disorders
Blindness

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28
Q

What is aneuploidy?

A

Abnormal number of chromosomes
Occurs during cell division when chromosomes do not separate equally between two daughter cells
A chromosomal abnormality resulting in genetic disorders because of extra or missing chromosomes

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29
Q

What happens as a result of aneuploidy?

A

Monosomic condition (only one copy of a chromosome is present instead of two; 2n - 1)
Trisomic condition (one extra copy of a chromosome; 2n + 1)
Nullisomic condition (no chromosome of that chromosome pair is present; 2n -2) - generally a lethal condition

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30
Q

What are the most common aneuploidys?

A

Trisomy 21, 18, and 13

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31
Q

What is a knockout mouse?

A

A genetically engineered mouse with specific gene(s) artificially deleted or inactivated from its genome
Knock out mice have been used to study many human diseases including cancer and hearing loss

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32
Q

What is cellular homeostasis?

A

The tendency of an organism/cell to regulate its internal conditions, such as the chemical composition of its body fluids, so as to maintain health and functioning, regardless of external conditions

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33
Q

What is a phenocopy?

A

An environmentally caused trait that mimics a genetically determined trait
The trait resembles symptoms of a Mendelian disorder or
It mimics inheritance by occurring in certain relatives

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34
Q

What is an example of a phenocopy?

A

Thalidomide exposure
A phenocopy of phocomelia
Hair loss from chemotherapy
A phenocopy of the genetic disorder alopecia

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35
Q

What is pleiotropy?

A

The diverse effects of one gene or gene pair on several organ systems and functions resulting in multiple phenotypic effects in the body

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36
Q

What is an example of a pleiotropy?

A

Marfan’s syndrome

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37
Q

What is marfan’s syndrome?

A

Autosomal dominant genetic disorder of connective tissue
Above average height
Tall, thin, long fingers (arachnodactyly)
Heart problems (aneurysm of the aorta, most serious)
Dislocated lenses of the eyes
Skeletal problems such as scoliosis, abnormal joint flexibility, and frontal bossing of the forehead
Speech disorders resulting from symptomatic high palate and small jaw

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38
Q

What famous person was suspected to have marfan’s syndrome?

A

Abraham Lincoln

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39
Q

How do you classify chromosomal abnormalities?

A

Number and structure

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40
Q

What are the different types of single gene defects?

A

Autosomal dominant
Autosomal recessive
X-linked dominant
X-linked recessive
Y-linked

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41
Q

Are human chromosomes grouped together by size?

A

Yes

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42
Q

Are chromosomes also grouped together by where the centromere is?

A

Yes

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43
Q

What are all the different variations of centromere location?

A

Subcentric - p and q are unequal
Metacentric - p and q are roughly equal in length
Acrocentric - p arm is short (chromosomes 13, 14, 15, 21, 22, and Y)
Telocentric - centromere is located at the terminal end
Holocentric - Entire chromosome acts as a centromere

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44
Q

What two variations of centromere locations are not present in humans?

A

Telocentric and holocentric

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45
Q

What are the main two generalizations of chromosomal abnormalities?

A

They have adverse effects on many parts/structures of the body
Most people with unbalanced chromosomes have pre- or post- natal onset growth deficiencies and intellectual disability

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46
Q

What are some exceptions to these chromosomal generalizations?

A

Some sex chromosome disorders that may have few if any recognizable phenotypic anomalies
Very small deletions or duplications of chromosome material in any chromosome

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47
Q

What is mendelian or monogenetic inheritance?

A

The inheritance of conditions caused by a single gene mutation

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48
Q

What are the two important laws of mendelian inheritance?

A

Law of segregation and law of independent assortment

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49
Q

What is the law of segregation?

A

The idea that each parent passes on a randomly selected gene copy or allele to their offspring
Not passing both genes, only one from mom and one from dad

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50
Q

What is the law of independent assortment?

A

Separate genes for separate traits are passed from parents to offspring independently of one another
They have no influence on one another

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51
Q

What does the law of independent assortment only hold true for?

A

Genes that are not in close proximity to each other
Genes that are close can be affected by another gene

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52
Q

Are most cases of genetic deafness today recognized as monogenetic (caused by a mutation of a single gene)?

A

Yes

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53
Q

T/F: Proteins coded by genes related to hearing loss are involved in many functions in the ear

A

True

54
Q

What are some examples of some of these proteins that are coded by genes related to hearing loss?

A

Cochlear fluid homeostasis
Ionic channels
Stereocilia morphology and function
Synaptic transmission
Gene regulation

55
Q

What is autosomal dominant?

A

One gene in a gene pair is mutated
Dominates the normal gene and caused an abnormal phenotype

56
Q

What are some characteristics for autosomal dominant inheritance?

A

Vertical transmission
50% risk to offspring per pregnancy
Unaffected individuals cannot transmit the disease
Males and females equally affected
Variable expressivity and penetrance

57
Q

Are individuals with autosomal dominance heterozygotes or homozygotes?

A

Heterozygotes

58
Q

What is expressivity?

A

The severity of the genetic condition apparent for the affected individual
Mild to moderate to severe
Dimmer switch

59
Q

What is penetrance?

A

The frequency of occurrence usually expressed as a percentage
You either show it or you don’t
On/off switch

60
Q

Can autosomal dominant conditions appear as though they skip a generation?

A

Yes
You can carry a gene without expressing it
Some manifest later in life in the presence of environmental factors or modifier genes

61
Q

Do people with autosomal dominant traits need to have a parent with the trait?

A

Yes, unless it occurred by spontaneous mutation

62
Q

What is an example of variable expression of phenotype?

A

Waardenburg syndrome

63
Q

What are some characteristics of autosomal recessive traits?

A

Two identical copies of the gene are required
25% chance of occurrence per pregnancy
Obligate carrier (heterozygous) parents
Horizontal family pattern
Family members of the same generation are affected but not in other generations
Males and females are equally affected
Consanguinity is common
Founder effect

64
Q

What is the founder effect?

A

Shared genetic ancestry/limited gene pool resulting in genetic conditions seen far more commonly in certain ethnic groups

65
Q

What are obligate carriers?

A

When a child has an autosomal recessive trait, both parents have to be carriers

66
Q

What is complementary mating?

A

Different recessive deafness gene in each parent
Every child will be hearing

67
Q

What is non-complementary mating?

A

Each parent has the same recessive deafness gene
Every child they have will be deaf

68
Q

What is x-linked inheritance?

A

Inheritance passed down by the X chromosome

69
Q

Can x-linked inheritance be dominant or recessive?

A

Yes
Based on whether or not a female manifests signs of diseases or is only a carrier*
If females are carriers with no sign of disease – X-linked recessive
If females manifest some signs of the disorder – X-linked dominant

70
Q

Are males more severely effected by x-linked disorders?

A

Yes

71
Q

If the trait is recessive (x-linked), will the daughter have it?

A

No, she will only be a carrier

72
Q

If the trait is dominant (x-linked), will the daughter have it?

A

Yes

73
Q

Is there male to male transmission for x-linked traits?

A

No
The dads only give the Y to their sons

74
Q

Since males only have one X, what do they call all the genes of the X?

A

Hemizygous

75
Q

Will a gene error on the X in males cause a disease?

A

Yes
Because there is no corresponding paired X chromosome with a good gene to balance the bad gene making males affected - psuedo-dominance

76
Q

What is pseudo-dominance?

A

Males only have one X, so any recessive trait on the X becomes dominant

77
Q

What is the difference between heterozygous and hemizygous?

A

Heterozygous – same chromosomes, different genes
Hemizygous – different chromosomes

78
Q

Do females have pseudo-dominance?

A

No, they have two X’s
If they have one bad one, it’s balanced out by a good one

79
Q

What are some characteristics of x-linked recessive traits?

A

No father to son transmission
Transmission from unaffected (normal phenotype) female carriers to males
All daughters of a male with the trait will be carriers
Carrier females will have a
50% chance to have sons with the abnormal trait
50% chance to have carrier daughters
50% chance of having a normal offspring
The abnormal trait may be transmitted through a series of carrier females

80
Q

What are some examples of x-linked recessive inheritance?

A

Color blindness
Hemophilia
X-linked hearing loss with stapes gusher
Muscular dystrophy

81
Q

Is x-linked dominant inheritance rare?

A

Yes

82
Q

Will a female with an X-linked dominant trait manifest the disease?

A

Yes
They will have it regardless of what the other X chromosome is

83
Q

What is the probability of sons and daughters to inherit the condition from their father with an x-linked dominant trait?

A

50%
The daughter can be affected if the father is affected and not just be a carrier
But the son is unaffected even if the father is affected

84
Q

How do you differentiate an X-linked recessive hearing loss from an X-linked dominant one?

A

If the mother is affected, each offspring has a 50% chance of being affected
Look carefully at the hearing of male offspring of the father
The son should have normal hearing because he inherits the normal Y chromosome from the father
If the father has an X-linked dominant gene passed on to his female offspring, she will have a hearing impairment
The daughter can be affected if the father is affected and not just be a carrier
But the son is unaffected even if the father is affected

85
Q

What are the different transmission traits for x-linked dominance?

A

Chance of transmission from mother to son and daughter; both genders will be affected
Transmission from affected father to daughter
NO transmission from affected father to son (normal Y chromosome)

86
Q

What is an example of x-linked dominant traits?

A

Alport’s syndrome
Collagen gene mutation
Affects BM of the cochlea - hearing loss
Affects BM of kidneys - glomerulonephritis, kidney failure
May also affect eyes

87
Q

Are there y-linked inheritance patterns?

A

Yes
They are very rare

88
Q

Are Y-linked traits only passed to boys?

A

Yes
Traits encoded by genes on the Y chromosome are passed directly from father to son
No father to daughter transmission

89
Q

Is there a specific region on the Y chromosome that determines gender?

A

Yes
It is the SRY region

90
Q

What are many of these Y-transmitted traits involved in?

A

Abnormal male sexual development
May be infertile
So, it doesn’t pass onto future generations
That is why it is so rare
Not all infertile, but a lot are infertile or have low fertility

91
Q

What is multifactorial inheritance?

A

Traits resulting from the interplay of multiple environmental factors with multiple genes
Most commonly associated with sporadic gene mutations

92
Q

What is an example of multifactorial inheritance?

A

Oculo-Auricular-Vertebral (OAV) spectrum disorder
Consists of three rare disorders that may be intimately related to each other
It maybe a range of severity of the same disorder
Rarely maybe inherited as an AD or AR disorder

93
Q

What is polygenic inheritance?

A

Traits or diseases caused by the impact of many different genes
Each gene has only a small individual impact on the phenotype
Traits are quantitative rather than qualitative i.e., the more severe the manifestation, the more predisposing genes are involved

94
Q

What is an example of polygenic inheritance?

A

Cleft lip/palate
Spina bifida

95
Q

Who were the ancestors of present-day mitochondria?

A

Free-living bacteria that adapted to living inside of primitive eukaryotic cells

96
Q

What is the mitochondria like today?

A

Over time most genes carried on the bacterial chromosomes were lost
But mitochondria today still carry DNA molecules that encode information for ~37 mitochondrial genes
Of those 37 genes, 13 genes still encode proteins that function in energy production

97
Q

Is the diagnosis of mitochondrial disorders difficult?

A

Yes, it is hard to isolate these genetic conditions
A wide variety of dysfunction in multiple organ systems should raise suspicions of a mitochondrial disorder

98
Q

Does mitochondrial inheritance obey the rules of classic Mendelian transmission?

A

No
During meiosis, mitochondria are passed only from the mother to the oocyte

99
Q

Why does mitochondrial inheritance only come from mom?

A

Sperm sheds its cytoplasm and mitochondria are only found in the cytoplasm

100
Q

What is another phrase for a mitochondrial trait?

A

Eve gene

101
Q

What is the likelihood of a child inheriting a mitochondrial condition from their mother?

A

100% of all children being affected

102
Q

Does mitochondrial DNA have a higher spontaneous mutation rate than DNA in nuclear genes?

A

Yes

103
Q

Why does mitochondrial DNA have a higher spontaneous mutation rate than DNA in nuclear genes?

A

Maybe because mtDNA evolves 5 to 10 times more rapidly than genomic DNA

104
Q

Why do syndromes occur when the mitochondria is affected?

A

Syndromes occur as a result of the affected mitochondria being unable to meet the metabolic demands of the tissues

105
Q

What kinds of tissues does mitochondrial disorders affect?

A

Predominant in tissues with high energy demands such as muscles but can affect multiple unrelated systems of the body
Initially mitochondrial transmission was thought to cause only neuromuscular disorders but now known that it can present with many different phenotypes

106
Q

What happens when division happens faster?

A

It is more likely there are mistakes

107
Q

What is Leber’s hereditary optic neuropathy an example of?

A

Mitochondrial inheritance

108
Q

What happens in Leber’s hereditary optic neuropathy?

A

Sudden loss of central vision
Optic nerve damaged at ~20 years of age
Predisposition to deafness from increased susceptibility to aminoglycoside ototoxicity
Also associated with maternally transmitted disorders such as diabetes
Degeneration of cochlear neural elements
Degeneration of portion of CN VIII in the cochlea

109
Q

What is aminoglycoside ototoxicity?

A

Aminoglycosides are antibiotics
With this mutation, one dose runs the risk of a severe to profound loss
Most of the time, dose and duration will determine the ototoxic loss
The larger the dose for a longer period of time = more of a loss

110
Q

Does aminoglycoside ototoxicity
affect DNA?

A

No
Mutation happens on ribosomal RNA
Those code for proteins
This is the result
Gene mutation; deletion of adenine with substitution of guanine - A to G of the ribosomal RNA gene
Gene mutation; deletion of thymine with substitution of cytosine - T to C of the ribosomal RNA gene

111
Q

What is genomic imprinting?

A

A process in which the phenotype differs depending upon which parent transmits a particular allele or chromosome

112
Q

What are examples of genomic imprinting?

A

Prader Willi syndrome and Angelman syndrome

113
Q

What is Prader Willi syndrome?

A

Deletion of chromosome 15 (del 15q11-13) of paternal origin
Small, floppy infants with small hands and feet
Intellectual disability
Obesity and uncontrollable eating and food cravings
Child does not enter puberty because the sex glands produce little or no hormones - cannot reproduce
Orthopedic issues later in life
Can have a normal life span if eating and associated obesity and diseases (e.g., diabetes) are controlled

114
Q

How is Prader Willi syndrome inherited?

A

Typically starts as a spontaneous mutation that is passed down
But cannot continue to be passed down because they cannot reproduce

115
Q

What is Angelman syndrome?

A

Deletion of chromosome 15 (del 15q11-13) of maternal origin
Intellectual disability
Developmental delay
Seizures
Happy demeanor
Laughs uncontrollably and excessively
Poor muscle coordination
Gait ataxia

116
Q

What is genetic anticipation?

A

The worsening of symptoms of a genetic disease from one generation to the next

117
Q

What is allelic expansion?

A

Increase in gene size
Caused by an increase in the number of the trinucleotide base sequences
As the number of these genes increase, the severity gets worse and worse

118
Q

Is anticipation caused by allelic expansion?

A

Yes

119
Q

What are some examples of genetic anticipation and allelic expansion?

A

Myotonic dystrophy
Huntington’s disease
Tay Sachs
Fragile X syndrome

120
Q

What is myotonic dystrophy?

A

Autosomal dominant
Expansion of the gene on chromosome 19
Repeat of base triplets CTG
Normal = 5 to 37 copies of CTG
Affected = 50 to 72,000 copies of CTG

121
Q

What are some signs and symptoms of myotonic dystrophy?

A

Drooping eyelids
Facial weakness
Mild to severe muscle weakness

122
Q

What is Huntington’s disease?

A

Autosomal dominant
Gene on the tip of chromosome 4p
Repeat of base triplets CAG
Normal = 6 to 37 copies of CAG
Affected = 35 to 121 copies of CAG

123
Q

What are some signs and symptoms of Huntington’s disease?

A

Adult onset
Loss of muscle coordination and control
Deterioration of intellectual function
Generally early death

124
Q

What is Fragile X syndrome?

A

X-linked dominant pattern with variable expressivity
Females and males are both affected
Caused by mutations in the FMR1 gene
FMR1 gene provides instructions for making a protein called fragile X mental retardation 1 protein (FMRP)
Tip of the X chromosome has a fragile site
Triplet repeat of CGG
Normal = 5 to 40 repeats
Fragile X = > 200 repeats

125
Q

Is fragile X the most common form of inherited intellectual disability in boys?

A

Yes
Males can be normal or mild to severally affected
Intellectual disability is less common in females

126
Q

Do people with fragile X typically have delayed development of speech and language?

A

Yes

127
Q

Do people with fragile X may have ADHD as well?

A

Yes

128
Q

What are some physical features of fragile X?

A

Long jaw
Big head
Large ears

129
Q

Is hearing loss typically associated with fragile X?

A

No

130
Q

If there are carriers involved, what kind of pattern is it not?

A

AD

131
Q

Is consanguinity an issue with AD transmission?

A

No

aude 5310 - embryology (16 decks)

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