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AUDE 5310 > Patterns of inheritance > Flashcards

Patterns of inheritance Flashcards

1
Q

what determines generations in pedigrees

A

Roman numerals (I, II, III…) symbolize generations

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2
Q

what determines birth order in a pedigree

A

Arabic numerals (1, 2, 3…) symbolize birth order within each generation

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3
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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4
Q

what is the goal of a pedigree

A

The object of a pedigree is to show and analyze the history of inherited traits through generations in a family

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5
Q

can pedigrees prove mode of inheritance ?

A

Pedigrees can frequently rule out, but not necessarily prove, a certain mode of inheritance

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6
Q

what must be included in a pedigree?
(11)

A

Proband
Race/ethnicity
First name or initials of relatives
people who have the disease
their age
age of death
Adoption status
Pregnancy/abortion
Consanguinity (mating within close relatives)
Marriage/divorce
Date pedigree obtained

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7
Q

what is a proband ?

A

the person being studied
it is the first affected family member seeking medical help for a possible genetic disorder
The person who is seeking the information

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8
Q

where to start on the pedigree

A

It is helpful to start in the middle of the page

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9
Q

how should mating be illustrated on pedigree?

A

Male partners to the left and female partners to the right connected by a single straight line

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10
Q

how should birth order be illustrated on pedigree?

A

Oldest to youngest with the oldest on the left and the youngest on the right

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11
Q

what is consanguinity?

A

mating with someone in the family (not siblings or parents)

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12
Q

what are monozygotic twins?

A

Twins that develop from a single fertilized egg

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13
Q

are monozygotic twins fraternal or identical?

A

identical (same sex)

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14
Q

How do monozygotic twins happen?

A

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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15
Q

are dizygotic twins fraternal or identical

A

fraternal

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16
Q

how does dizygotic twins happen?

A

Develop from simultaneous shedding of two ooctyes, and fertilized by two different sperms, i.e., fraternal twins of different genders

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17
Q

look at pedigree symbols slide 14

A
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18
Q

what is locus

A

Specific location of a gene or DNA sequence on a chromosome
each gene is found in a specific place on the chromosome

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19
Q

what does Homozygous/homologous mean

A

same gene from each parent on each chromosome

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20
Q

what does Heterozygous mean

A

different gene from each parent on each chromosome

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21
Q

what does Heterogeneity mean

A

many genes are involved but the result (phenotype) will still be the same
Many genes but one phenotype
ex. hearing loss/ deafness
blood clotting disorders
blindness

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22
Q

P arm

A

short arm

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23
Q

q arm

A

long arm

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24
Q

what is region in terms of chromosomes address

A

Each arm subdivided into numbered regions, beginning from the centromere

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25
Q

what is band in terms of addressing a chromosome?

A

Within each region identified by numbers

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26
Q

how do you write a descriptive address for chromosomes?

A

chromosome number, arm, region, band

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27
Q

what does ploidy mean

A

number

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28
Q

what is a diploid cell?

A

Double the number of chromosomes found in a mature germ cell (46 chromosomes)

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29
Q

are human somatic cells haploid or diploid?

A

Human somatic cells are diploid cells with 23 pairs of chromosomes (46 individual chromosomes)
44 somatic and two germ chromosomes (XX or XY)

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30
Q

how many chromosomes are in haploid cells

A

23

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31
Q

what are germ cells

A

eggs and sperms (sex cells)

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32
Q

are germ cells haploid or diploid

A

Germ cells are haploid cells with half the number of chromosomes as the somatic cells

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33
Q

what is aneuploidy

A

Abnormal number of chromosomes

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34
Q

what causes aneuploidy to happen

A

Occurs during cell division when chromosomes do not separate equally between two daughter cells

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35
Q

what is the result of aneuploidy?

A

A chromosomal abnormality resulting in genetic disorders because of extra or missing chromosomes
-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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36
Q

what is a knock out mouse

A

A genetically engineered mouse with specific gene(s) artificially deleted or inactivated from its genome

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37
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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38
Q

what are the most common aneuploidy?

A

trisomy 13, 18, 21

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39
Q

what is phenocopy

A

An environmentally caused trait that mimics a genetically determined trait
(it’s not inherited but it mimics it)
-The trait resembles symptoms of a Mendelian disorder or
-It mimics inheritance by occurring in certain relatives

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40
Q

what are examples of phenocopy

A

thalidomide exposure (a phenocopy of phocomelia)
hair loss from chemotherapy (a pheoncopy of the genetic disorder aloperca)

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41
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
Pleiotropy occurs when one gene influences two or more seemingly unrelated phenotypic trait
onegene infulencing multiple phenotypics effect on the body

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42
Q

whats an example of pleiotropy and what symptoms would appear with someone with that condition?

A

Marfan’s syndrome
-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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43
Q

what famous president could have marfans syndrome

A

Abraham Lincoln

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44
Q

what are classifications of genetic disorders

A

By chromosomal abnormalities
-Number
-Structure

By single gene defect
-Autosomal dominant
-Autosomal recessive
-X-linked dominant
-X-linked recessive
-Y-linked

By mitochondrial genetic defect

By multifactorial/polygenic defects

By environmental influences – generally spontaneous mutation

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45
Q

What do chromosomal abnormalities affect?

A

-Size
-Centromere location
-subcentric/ submetacentric
-metacentric
-acrocentric
-telocentric
holocentric

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46
Q

what does subcentric/submetacentric mean?

A

The chromosome’s p & q arms’ lengths are unequal
located a bit above on the center of the centromere

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47
Q

what does metacentric mean?

A

The two arms of chromosome are roughly equal in length
it’s located in the middle

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48
Q

what does acrocentric mean

A

P arm is so short that is hard to observe, but still present
almost at the end of the centromere

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49
Q

what chromosomes in humans are acrocentric ?

A

13, 14, 15, 21, 22, & Y

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50
Q

what does telocentric mean

A

Centromere is located at the end of the chromosome

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51
Q

are telocentric present in humans ?

A

no

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52
Q

what does holocentric mean?

A

Entire length of the chromosome acts as the centromere

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53
Q

are holocentric present in humans

A

no. but they’re present in worms

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54
Q

when should chromosomal abnormalities be studied

A

Chromosomal studies should be performed for any individual with multiple malformations and unknown overall diagnosis

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55
Q

what are generalizations regarding chromosomal abnormalities that can recognize conditions?
how do you know if it’s a chomosomal abnormality or not ?

A

1)chromosomal abnormalities have adverse effects on many parts/structures of the body
-nevertheless someone with 2 anomalies are unlikely to have chromosomal abnormalities
2)most people with unbalance chromosomes have pre- or post-natal onset growth deficiencies and intellectual disability
-someone with normal growth patterns, and intelligence, and psychomotor development are not a candidate for chromosome abnormalities

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56
Q

what are some exceptions to generalizations about chromosomal abnormalities

A

-sex chromosomes
-Very small deletions or duplications of chromosome material in any chromosome

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57
Q

what is the first law of mendelian/ monogenetic inheritance

A

it’s called the law of segregation
what it is:
-Every individual has a pair of alleles for every particular trait, which segregate or separate during cell division
-Each parent passes a randomly selected gene copy or an allele to his or her offspring
(whatever gene we get is random)
-The offspring then receives his or her own pair of alleles of that gene for that trait by inheriting sets of homologous chromosomes from the parent organisms
(one gene from mom and dad in EVERYTHING)

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58
Q

what is mendelian/monogenetic inheritance?

A

It is the inheritance of conditions caused by mutation of a single gene
(only one gene is affected)

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59
Q

What is the second law of Mendelian/monogenetic inheritance

A

it’s called the law of independent assortment
what it is:
-It states that separate genes for separate traits are passed from parents to offspring independently of one another
-More precisely, the law states that the biological selection of a particular gene in the gene pair for one trait that is passed to the offspring has nothing to do with the selection of the gene for any other trait

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60
Q

most genetic deafness recognized today by…

A

1)monogenic disorders caused by mutation of a single gene and broadly classified by the mode of inheritance (autosomal dominant, autosomal recessive, x linked, and mitochondrial)
2) and by the presence of phenotypic feature
ex. syndromic (something w/ hl) and non-syndromic (hl is the only problem)

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60
Q

When does the second law of mendelian/monogenetic inheritance apply

A

it only applies for genes that are not linked to one another
(genes that are not in close proximity to one another on the same chromosome )

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61
Q

Proteins coded by genes related to hearing loss are involved in what functions in the ear?

A

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

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62
Q

What is autosomal dominant (AD)?

A

One gene in a gene pair is mutated but this change dominates the normal gene and causes an abnormal phenotype
-Affected individuals are heterozygotes (can come from mom or dad, it doesn’t matter)

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63
Q

what are characteristics of AD 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

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64
Q

what does expressivity mean?

A

refers to the severity of the genetic condition apparent for the affected individual

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65
Q

what does penetrance mean?

A

refers to frequency of occurrence, usually expressed as a percentage

66
Q

why might some AD gene mutations appear later in life?

A

because of the presence of environmental factors or modifier genes

67
Q

D

A

dominant allele for deafness

68
Q

d

A

allele for hearing

69
Q

How many AD inheritance are there?

A

A person can have one of 3 patterns

70
Q

Genotype Phenotype
DD = homozygote deaf
Dd = heterozygote deaf
dd = homozygote hearing

A
71
Q

Summary of characteristics of AD traits

A

-Only one copy of the gene is needed to produce the phenotype; affected individuals are heterozygotes
-Chance of occurrence per pregnancy is ½ (50%)
-Vertical family pattern
-Persons with the trait have a parent with the trait unless they represent a spontaneous mutation
-If the line is broken it stays broken
Incomplete penetrance
-Variable expressivity
-Male : female = 1:1

72
Q

What is an example of variable expression of the phenotype

A

waardenburg syndrome

73
Q

Dd means?

A

Heterozygote

74
Q

dd

A

homozygote

75
Q

look at risks of calculating AD inheritance

A
76
Q

For autosomal dominant, if the person had the trait, what are the chances they pass it to their kids?

A

50%

77
Q

For autosomal dominant, if the person didn’t have the trait, what are the chances they pass it to their kids?

A

0% because he never had it

78
Q

do carrier types exist for autosomal dominant?

A

no, only for recessive

79
Q

a vertical transmission is seen in?

A

autosomal dominant

80
Q

a horizontal gene is seen in?

A

autosomal recessive

81
Q

What is the percentage a child might get the trait in recessive?

A

25%

82
Q

what is the chances the kid could get the trait in dominant

A

50%

83
Q

How do recessive genes work?

A

Two identical copies of the gene are required
(homozygous offspring)

84
Q

Which generation is affected in recessive?

A

Family members of the same generation are affected but not in other generations

85
Q

Is consanguinity common for recessive inheritance ?

A

yes

86
Q

Who is more likely to get affected in recessive inheritance?

A

Males and females are equally affected

87
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

88
Q

where is the founder effect mainly seen?

A

in recessive inheritance

89
Q

What can recessive inheritance patterns look like?

A

Genotype Phenotype
RR = homozygous hearing
Rr = heterozygous hearing, carrier
rr = homozygous deaf

90
Q

what might the genes for a carrier look like ?

A

Rr (heterozygous)

91
Q

What are risk factors of autosomal recessive inheritance?

A

Consanguinity

92
Q

What are obligate carriers

A

Both parents have to have the gene in order for their offspring to inherit the trait

93
Q

Can the trait still pass down the gene, even tho they have different deaf genes?

A

no, it has to be the same identical gene in order to manifest

94
Q

What is the difference between carriers and obligate carriers?

A

obligate carriers, the parents offspring come out with the condition. Carriers, they carrier the gene but the kids don’t manifest with the gene

95
Q

how to calculate risk of inheritance in recessive

A

Complementary mating
Non-complementary mating
Risk for unaffected sibling to be a carrier
Pseudo-dominance

96
Q

What is Pseudo-dominance

A

A situation in which inheritance of an autosomal recessive trait mimics an autosomal dominant pattern; one recessive allele could cause expression of the trait

97
Q

where is Pseudo-dominance seen?

A

X linked recessive inheritance of male offspring
x linked from dad

98
Q

an example of complementary mating is when

A

If the parents had different forms of autosomal recessive deafness, all of their children would be hearing. kids would be carriers for 2 different affected genes

99
Q

what is an example of non-complementary mating?

A

the parents have the same recessive form of deafness, all of their children will be deaf

100
Q

How are x linked inheritance divided into?

A

x linked recessive or x linked dominant

101
Q

How do you determine if it’s x linked recessive or x linked dominant if it’s from mom?

A

-if the mom is a carrier and she shows no sign of the disease, it’s X linked recessive
-if mom is a carrier and does show signs of a disease, it is X linked dominant

102
Q

Who is more affected in x linked disorders?

A

men because they don’t have a X balancing chromosome

103
Q

If the trait is recessive in affected males, how are their daughters going to be affected?

A

daughters will be carriers

104
Q

if the male has a dominant X linked gene, how will the daughter be affected?

A

She will manifest the trait

105
Q

how do you define an X linked chromosome?

A

Traits controlled by genes on the X chromosome are defined as dominant or recessive by the phenotype of the females
(by the phenotype of mom)

106
Q

are two copies of the same gene necessary for X LINKED RECESSIVE

A

no, because Men only have a single X chromosome, so they have only one copy of any gene on the X chromosome

107
Q

Men are ___ for all genes on the X chromosome

A

hemizygous (each chromosome is different)

108
Q

Will X linked recessive diseases affect men?

A

yes because they only have one X.
there is no corresponding paired X chromosome with a good gene to balance the bad gene making males affected making it psuedo-dominance

109
Q

will an an X linked recessive disease affect women?

A

no. because they have 2 X chromosomes. one good x gene to balance the bad gene. That’s why females are always carriers

110
Q

What are characteristics of X linked recessive inheritance ?

A

1) no father to son transmission
2)Transmission from unaffected (normal phenotype) female carriers to males (carrier women give it to son)
3)All daughters of a male with the trait will be carriers
4)The abnormal trait may be transmitted through a series of carrier females

111
Q

Carrier females of x linked recessive traits will have :

A

-50% chance to have a son with the abnormal trait
-50% chance to have daughters who are carriers
-50% chance of having a normal off spring
This all depends if they give their child the bad or good x chromosome

112
Q

what are x linked recessive patterns we can see in genes ?

A

Genotype Phenotype
XX = homozygote hearing female
Xx = heterozygote hearing female
XY = hemizygote hearing male
xY = hemizygote deaf male

113
Q

What are examples of x linked recessive inheritance ?

A

Color blindness
Hemophilia
X-linked hearing loss with stapes gusher
Muscular dystrophy (Duchenne-type)

114
Q

is x linked dominant common?

A

no, it’s rare

115
Q

how will x linked dominant chromosome manifest?

A

The female with the abnormal gene on one X chromosome will manifest the disease condition regardless of what is on the other X chromosome
-therefore, both son and daughter have a 50% chance of inheriting the conditions from the mother

116
Q

how do you tell apart x linked recessive and x linked dominant if it’s from dad?

A

-LOOK AT THE FATHER TO SON TRANSMISSION
(the son should have normal transmission because he only gets a y chromosome from dad)
-LOOK AT DAUGHTER TRANSMISSION
(if he has it then the daughter will have it, she won’t be a carrier anymore)
-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

117
Q

what are transmission traits in x linked dominant inheritance?

A

-both genders are affected if it’s coming from mom
-if dad is affected then the daughter will be too (she’s getting his only good X)
-father can not pass it down to son (cause he’s giving him his y)

118
Q

what is an example of x link dominant trait

A

alport’s syndrome

119
Q

does y linked patterns exist ?

A

rare, but yes

120
Q

how is y linked chromosome trasmitted?

A

father to son

121
Q

why are y linked traits only expressed in male offspring?

A

-All males are hemizygous for all genes on the Y chromosome
-No balancing of the mutant Y gene by X or another Y gene on the Y chromosome

122
Q

what are nontraditional modes of inhertiance?

A

1)Multifactorial
2)Polygenic

123
Q

what are multifactorial traits ?

A

Traits resulting from the interplay of multiple environmental factors with multiple genes

124
Q

what are multifactorial traits most commonly associated?

A

with sporadic (spontaneous) gene mutations

125
Q

what is an example of multifactorial traits?

A

Oculo-Auricular-Vertebral (OAV) spectrum disorder

126
Q

what are polygenic traits?

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

127
Q

what is an example of polygenic traits?

A

cleft lip/ palate
spina bifida

128
Q

does Mitochondrial inheritance obey the rules of classic Mendelian transmission

A

no

129
Q

how is mitochondrial cells transmitted?

A

-During meiosis, mitochondria are passed only from the mother to the oocyte
-Because sperms do not contribute cytoplasm during fertilization and mitochondria are found only in cytoplasm

130
Q

HOW are mitochondrial traits passed down thru?

A

they’re passed down thru the mom’s eve gene
-dad can’t pass it down
-both sexes from mom are affected

131
Q

what is the risk factor of mom passing down mitochondrial traits?

A

100 because we have mitochondria in everything

132
Q

What has a higher spontaneous mutation rate, mitochondrial dna or DNA in nuclear genes? and why?

A

-Mitochondrial DNA (mtDNA) has a higher spontaneous mutation rate than DNA in nuclear genes
-because mtDNA evolves 5 to 10 times more rapidly than genomic DNA

133
Q

why do syndromes occur in mitochondrial syndromes?

A

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

134
Q

where are mitochondrial disorders prominent?

A

Mitochondrial disorders are predominant in tissues with high energy demands such as muscles but can affect multiple unrelated systems of the body

135
Q

what is an example of a mitochondrial disorder?

A

Leber’s hereditary optic neuropathy:
-Sudden loss of central vision
-Optic nerve damaged at ~20 years of age

136
Q

why do mitochondrial disorders concern us

A

because Histopathologic studies show degeneration of cochlear neural elements and degeneration of portions of cn 8 in the cochlea

137
Q

what is genomic imprinting?

A

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

138
Q

what is an example of genomic imprinting?

A

-prader willi syndrome
-Angelman syndrome

139
Q

how does prader willi syndrome occur?

A

Deletion of chromosome 15 (del 15q11-13) of PATERNAL origin

140
Q

what are some characteristics of prader willi syndrome disorder?

A

-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

141
Q

how does Angelman syndrome occur?

A

Deletion of chromosome 15 (del 15q11-13) of MATERNAL origin

142
Q

what are some characteristics of Angelman syndrome?

A

-Intellectual disability
-Developmental delay
-Seizures
-Happy demeanor
-Laughs uncontrollably and excessively
-Poor muscle coordination
-Gait ataxia

143
Q

what is genetic anticipation

A

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

144
Q

what is allelic expansion

A

-it’s caused by an increase in the number of trinucleotide base sequence (increase in a gene)
- as the gene increases in number, the more severe the disorder becomes as the generations occur

145
Q

what is an example of anticipations and allelic expansions?

A

huntingtins disease, myotonic dystrophy, fragile x syndrome

146
Q

is myotonic dystrophy dominant or recessive?

A

dominant and is an expansion of the gene on chromosome 19

147
Q

what are symptoms of someone with myotonic dystrophy

A

-Drooping eyelids
-Facial weakness
-Mild to severe muscle weakness

148
Q

Is Huntington’s disease dominant or recessive

A

dominant and is a Gene on the tip of chromosome 4p

149
Q

what are signs of huntington’s disease?

A

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

150
Q

who is affected in fragile x syndrome?

A

mom has a 50% chance to giving it to both sexes
dad doesn’t give it to son, but he does give it to daughter.
(girls affected either way) follows x linked dominant patterns

151
Q

what is mutated in the fragile x syndrome

A

the FMR1 gene

152
Q

is fragile x more common in boys and girls, and what doe we typically see present ?

A

Most common form of inherited intellectual disability in boys
-intellectual disability is less in girls

153
Q

what id fragile X in charge of doing

A

FMR1 gene provides instructions for making a protein called fragile X mental retardation 1 protein (FMRP)

154
Q

what are other symptoms seen in fragil x syndrome?

A

-Delayed development of speech and -language
-May have ADHD
-Physical features
-Long jaw
-Big head
-Large ears

155
Q

is consanguinity an issue in autosomal transmission

A

NOOOOOOOOOOO

156
Q

summary of mitochondrial inheritance (eve gene)

A

-Fathers cannot pass on the trait to his children because the sperm loses cytoplasm prior to fertilization
-All children, male and female, of affected mothers have a 100% risk of being affected

157
Q

are carriers seen in autosomal dominant patterns of inheritance?

A

NOOOOOOO

158
Q

x linked dominant inheritance summary

A

-If father is affected, each female off springs has a 100% risk of being affected (father has only one X to donate)
-If mother is affected, each offspring (male & female) has a 50% chance of being affected (mother has two Xs and can donate either the normal or mutated X – 50% chance)

159
Q

summary of x linked recessive FATHER

A

All daughters are at a 100% risk of being carriers because father contributes an X chromosome to daughters

160
Q

x linked recessive summary MOTHER

A

-50% chance of carrier daughters (mother has one normal and one affected X chromosome
-But if sons inherit the bad X, then 100% affected even though it’s a recessive trait – Pseudo dominance – no balancing good X in males, who are hemizygous, so the recessive trait behaves as a dominant trait in sons

161
Q

can father pass an x linked disorder to son?

A

-No father-to-son (male-to-male) transmission for X-linked (recessive or dominant) patterns of inheritance
-Because father does not contribute an X chromosome to his son!

162
Q

what is complementary mating

A

-autosomal recessive
-Commonly seen with deafness/hard-of-hearing phenotype
-Both parents are deaf, but children are not because each parent’s deafness is due to different genes
-Recessive traits require identical genes from each parent to manifest the phenotype
-All children will be 100% carriers of two different deafness genes

163
Q

what is non-complementary mating

A

(autosomal recessive trait)
Both parents are affected and so are all children
Because both parents carry the same deafness genes

AUDE 5310 (4 decks)

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