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TBL 1. Inheritance Patterns (Guide Questions)
Terms in this set (120)
What is a disease?
An abnormal condition of a part, organ, or system of an organism resulting from various causes such as infection, inflammation, environmental factors, or genetic defect, and characterized by an identifiable group of signs, symptoms, or both.
What are signs?
Objective evidence of the disease.
What are some examples of a sign?
Rash, elevated body temperature, low red blood cell count.
What is a symptom?
Subjective evidence of a disease, only experienced by the patient.
What are some examples of a symptom?
Pain, anxiety, fatigue.
What is the difference between signs and symptoms?
Signs are objective in which they can be evaluated and observed by another. Symptoms are subjective in which they can only be experienced and observed by the individual undergoing them.
What is a phenotype?
An observable characteristic of a person.
What are some examples of phenotype?
Body height, body temperature, hemoglobin levels, activity of the phenylalanine hydroxylase enzyme
What are two methods in which most phenotypes are determined by?
1. Genotype (the genetic information of an organism or cell)
2. Environmental factors (Diet, infections, exposure to toxins, drugs, ect.
What is genotype?
The genetic information in an organism or cell (the DNA sequence) and may refer to the entire DNA sequence, a specific gene, or a group of genes.
What is a gene?
A molecular unit of hereditary information in living organisms which consists of a region of DNA sequence that encodes for a functional product of protein or RNA.
What a locus?
A site within a genome (or on a chromosome) which is often used to reference a gene location and synonymously with genes.
What is an allele?
A variant form of a gene.
At a DNA what are alleles?
Alleles at a DNA level are homologous genes which can differ by a small number of nucleotides or a large number (like gene deletions or partial deletions) which may be assocaited with disease.
What does polymorphisms mean?
A discontinuous genetic variation resulting the occurrence of several different forms or types of individuals among the members of a single species.
In natural selection, selection for a variant would be secondary to it's ______ ______?
In natural selection, selection against a variant would be a secondary to it's _______ ________?
The most common allele in the population would be referred to as the ___?
Wild-type allele could also be referred to as the ___ with some exceptions.
When a disease-causing allele is the most common allele it is referred to as the ______.
A permanent, heritable change in the DNA sequence is a _____.
How does a mutation relate to phenotype?
Often it does not have an effect on phenotype, but it can. It can also lead to pathogenic effects.
__________ drive evolution.
__________ is any genomic DNA sequence variant, occurring in the genome, and found in a significant proportion of the population (>1%).
How do rare variants differ from polymorphisms?
Polymorphisms and rare variants are both variants found in DNA sequence, however polymorphisms are found in >1% of the populations while rare variants only occur in <1% of the population.
Please note these terms are loosely used and sometimes used interchaneably.
Dominant and recessive only refer to _____ and more specifically how they are ______.
Dominant and recessive only refer to PHENOTYPES and more specifically how they are INHERITED.
What are Medel's Laws?
First Law: Segregation, Second Law: Independent Assortment, Third Law: Law of Dominance
What is the law of segregation?
Each individual carries two alleles of a characteristic but only one is passed on to the next generation at each mating.
Law of segregation works because the allele pairs one individual carries are seperated in the production of ____.
What is the law of independent assortment?
Members of different gene pairs segregate to offspring independently.
What is the law of dominance?
Traits do not "blend" therefore in heterozygous individuals one phenotype will be present which will be that of the dominant phenotype.
Mendel's Laws are generally true for traits which are determined by ______.
An exception to Mendel's Laws in traits determined by a singular gene is:
In the case of linkage which prevents Mendel's second law of independent assortment.
Why does Mendel's Laws appear untrue typically in humans?
Most human traits are secondary to multiple genes.
What is a carrier?
Someone who is heterozygous for a mutation, however as the mutation is recessive there are personally unaffected but are at risk of having affected offspring.
The terms dominant and recessive are only applicable to _____ not _____ because the inheritance must be ____.
Phenotypes; genotypes; observed
Approximately how many base pairs make up the human genome?
Approximately what percentage of the human genome varies in sequence?
Approximately how many base pairs of the human genome consists of variation?
What is a kindred?
All of the genetically related members of a family.
What is a pedigree?
A diagram of a kindred. (Example: A family tree)
In regards to a pedigree, the square, the circle, and the diamond represent?
The square represents males, the circle represents females, and the diamond represents an individual of unknown sex.
In regards to a pedigree typically, when a symbol is filled in, not filled in, denoted with vertical line down the middle of the symbol, or denoted with a dot in the middle of the symbol.
Typically filled in is an affected individual, not filled in is an unaffected individual, a vertical line is an unaffected individual who is a carrier, and a dot in the middle is an unaffected individual who is an obligate carrier.
In regards to a pedigree, a triangle and/or dot at the end of the line represents?
A miscarriage or abortion
In regards to a pedigree, a horizontal line represents _________ while a double horizontal line represents __________.
Mating/marriage; consanguineous mating/marriage (mating/marriage between relatives from the same ancestor at the 5th degree or closer)
In regards to a pedigree, vertical line represents _________while two diagonal lines protruding from the same location represent ________.
Offspring; offspring who are twins
In regards to a pedigree, when two diagonal lines protrudes from the same location and the secondary symptoms are not connected they are _____ while if the two symbols are connected they are ____.
Non-identical twins; identical twins
In regards to a pedigree, a slash through a symbol indicates ____.
In regards to a pedigree, a number in the box would be a simplified way to?
Represent that amount of individuals in that generation who are of the same gender and affected status. For example, an unshaded box with the number 2 would indicate two males who are unaffected.
In regards to a pedigree, generations are indicated through _______ numerals _____ down the tree.
In regards to a pedigree, individuals are identified within a generation via ______ numerals going ____-to-______.
In regards to a pedigree, what is a proband and what is a consultand and how are they denoted on the pedigree?
A proband is the member of the family with a genetic disorder (so affected) and is the first to have it brought to attention. The consultand is the an individual seeking counseling. Probands are denoted by being filled in red.
Can there be more than one proband?
There can be multiple porbands when the disease was ascertained by more than one source.
In regards to pedigree, who are considered first degree relatives?
Parents, siblings, and children
In regards to a pedigree, who are considered second degree relatives?
Aunts, uncles, niece, nephew, grand-parents, half-siblings
In regards to a pedigree, who are considered third degree relatives
In regards to a pedigree, are spouses relatives?
No, unless in cases of consanguinity.
In regards to a pedigree, what is the percentage of genes in common between different degrees of relationships?
First degree (50% of genes are in common), second degree (25% genes are in common), third degree (12.5% of genes are in common), fourth degree (6.25% of genes are in common), and so forth (decreasing by half each degree).
In medical genetics, typically diseases will have affected individuals who are ______ for the dominant gene.
In regards to autosomal dominant inheritance, an affected parent has a ___% change of transmitting the phenotype to each offspring.
In regards to autosomal dominant inheritance, ____________ generations are affected because:
Successive; there is no skipping of generations
In regards to autosomal dominant inheritance, males and females are affected with _____ frequency and severity, and also transmit the disease to their offspring with ___ frequency.
If there is male-to-male inheritance _____ can be ruled out.
X-linked inheritance pattern
In regards to autosomal dominant inheritance, what is the most common mating alleles and how does this relate to the potential offspring?
One affected partner with heterozygous Aa alleles and one unaffected partner with recessive homozygous aa alleles. This means that 50% of the offspring could receive the dominant allele leading to 50% of offspring being affected.
In autosomal inheritance a disease typically last ~___ generations before ____.
5; dying out
Why might an autosomal inheritance begin after 3 generations when generations prior have no had any affected individuals?
Novel/spontaneous mutation that occurred in the meiosis of one of the parents leading to gametes with the mutated genotype to give way to an observable phenotype.
In cases of novel/spontaneous mutations in gametes leading to autosomal dominant diseases presenting an affected individual their siblings would be very _____ to also be affected.
Examples of autosomal dominant diseases include:
Huntington Disease (neurological), Marfan Syndrome (growth development), Achondroplasia (dwarfism), and Osteogenesis Imperfecta (weak bones readily fractured).
As well as neurofibromatosis, polycystic kidney disease, and familial hypercholesterolemia.
In genetics what is penetrance?
The probability that individuals with specific genotypes will manifest the corresponding phenotype.
What is complete penetrance?
When an individual with a genotype, 100% of the time manifest the corresponding phenotype.
In genetics what is incomplete penetrance?
When an individual has a genotype, however does not manifest the corresponding phenotype.
What could be mistaken secondary to incomplete penetrance on a pedigree?
As skipping generation.
BRCA1 gene mutation is a genotype that leads to breast cancer as a phenotype, however when this does not occur it is an example of ______.
What is the formula for calculating the degree of penetrance on a pedigree?
(Degree of penetrance) = (Manifested Affected individuals) / (Affected Individuals with the Genotype)
What is variable expressivity and how might it be observed?
Variation in phenotype amongst individuals carrying the same genotype. For example phenotype might differ in the symptoms present or the severity of the symptoms.
What causes variable expressivity?
Other genetic influences, gene-environment interactions, and random chance.
Penetrance does not take into account ____ while variable expressivity does.
Severity (Penetrance is an "all-or-none")
_____________ is when a homozygotes display a greater or more severe phenotype than heterozygotes, appears as gene dosage.
Most diseases with a dominant inheritance pattern display _______ dominance like achondroplasia and familial hypercholesterolemia.
___________ is when two alleles determine different phenotypes and an individual with both alleles (heterozygote) will express both phenotypes.
Blood types is an example of ________.
In blood type the allele A and the allele B are _______ while O is ___________.
In an autosomal recessive disease in order for someone to be an affected individual when no one else in there family is what is required of their ancestry, generally speaking?
The affected individual must have two parents who are carriers of the recessive allele.
In an autosomal recessive disease, if both parents are carriers what is the percent chance the offspring will be affected?
In an autosomal recessive disease, it is typical to see a ________ or a ______ pattern of the pedigree. This is because:
Single affected individual; horizontal pattern (siblings); Autosomal recessive diseases are rare and in order to be affected one must receive a recessive allele from two carrier parents. Two carrier parents could therefore also have a chance of having multiple offspring who are affected.
In an autosomal recessive disease, males and females affected are ____ in frequency and severity as well as _____ in transmission frequency.
True or false: In an autosomal recessive disease, male-to-male inheritance is possible.
What are examples of autosomal recessive diseases?
Cystic fibrosis (changes in osmotic ion transfer-lung deficits), thalassemia (blood disease), sickle cell disease (blood disease), and many metabolic disorders (enzyme deficiencies) like Alkaptonuria, Phenylketonuria, Oculocutaneous Albinism, and Lysosomal Storage diseases.
When evaluating a pedigree what is an easy way to calculate the degree of relation?
Count the amount of continuous lines between the two subjects, lines are broken when another individual is between them.
When evaluating a pedigree what is an easy way to find any consanguineous matings?
Find complete loops in the pedigree.
The rarer the autosomal recessive disease, the more likely ____ is involved.
It is estimated that most people are carriers for ___ recessive alleles that if homozygous would be lethal.
Incestuous matings in genetics are ___ degree relatives which present the 3 main types of disorders are ________________, ______________, and ____________ at ___________ frequency than their non-incestuous counterparts.
first; intellectual impairments, autosomal recessive disorder, congenital malformation; greater/higher.
When a recessive trait mimics a dominant patter it is called ___________ and is secondary to the recessive allele being very _____.
Examples of pseudodominance include:
Type O blood (ABO blood types), blue eyes, sickle cell disease in parts of Africa, and Cystic Fibrosis in parts of Quebec.
What is complementation?
A mating between individuals with the same phenotype results in offspring without the phenotype. Mutants complement each other in which two genes that cause the same phenotype have come together to give heterozygotes.
What is locus heterogeneity?
Same phenotype due to mutations in different genes.
In autosomal recessive diseases, what is the percentage change that an unaffected sibling of an affected individual will be a carrier?
66.6% (Known as the 2/3 rule)
Reasoning: For there to be an affected individual the parents have to be heterozygous carriers meaning they have a Dd allele types meaning their offspring have a 25% chance of being dominant homozygous DD, 25% of being recessive homozygous dd, and 50% chance of being heterozygous Dd. However, the key word in this problem is unaffected sibling. As the sibling is unaffected it means they cannot be recessive homozygous changing the probability to 33.3% dominant homozygous DD and 66.6% heterozygous.
What are the three requirements for the 2/3 rule to apply?
1) Must be referencing autosomal recessive disease, (2) Only applies once they have been noted to be unaffected, (3) Neither parent can be affected (they both must be carriers)
In x-linked recessive diseases, family history of the disease can only be on the _____-side because:
Maternal; X-linked recessive diseases would require them to be on the X-chromosome meaning that in the male affected individual it would be the X chromosome donated by his mother which would have the recessive allele. (It is EXTREMELY rare for both the mother and father to have the recessive alleles on the X-chromosomes to donate to a daughter who would be homozygous for the recessive allele).
In x-linked recessive diseases, only ___ are affected this is because:
Men are affected; It is EXTREMELY rare for both the mother and father to have the recessive alleles on the X-chromosomes to donate to a daughter who would be homozygous for the recessive allele. However as men only receive one x chromosome from their mother they would only need one x chromosome with the recessive allele to show the phenotype.
In an x-linked recessive disease, _____-to-_____ transmission is impossible because:
Male-to-male; men donate the y chromosome to their sons (when determining the gender) meaning they cannot pass down a recessive x chromosome to a son.
What is hemizygous?
Having only one allele for a genotype.
What is an obligate carrier?
Someone who is not verified as a carrier, but secondary to the linage's phenotypes they would logically have to be a carrier.
In regards to an x-linked recessive diseases if there is no family history this maybe due to:
Spontaneous mutation found in gametes.
What are examples of x-linked recessive diseases?
Duchene muscular dystrophy (muscle disease), hemophilia (blood disease), red-green color blindness.
As well as androgen insensitivity syndrome, Hunter syndrome, X-linked severe combined immunodeficiency, and Menke's disease.
In regards to x-linked dominant diseases there is never ______-to-_____ transmission and women are ____ likely than man to be affected.
In x-linked dominant diseases, affected mothers have ___% of their sons affected and ___% of their daughters affected.
In x-linked dominant diseases, affected father have ___% of their sons affected and ___% of their daughters affected.
What are examples of x-linked dominant diseases?
Rett Syndrome (Brain development defect) and Fragile X Syndrome (Intellectual defect)
Additionally: Vitamin D-resistant rickets and Incontinentia pigmenti type 2
What is semi-dominance in x-linked diseases and how does it present in DMD and Rett Syndrome?
Most x-linked diseases show semi-dominance in which a disease displays some degree of dominance based on the allele differences. For example, in DMD female carrier (who is heterozygous) have some degree of muscle weakness while their affected male counterpart (who is hemizygous) has DMD. In Rett Syndrome, patients are mostly females ( who are heterozygous) while their male affected counterparts (those who are hemizygous) are usually miscarried.
In regards to mitochondrial Inheritance what is the linage of passing the genotypes and phenotypes?
Genotype passes from female carrier or affected individual to offspring with variable penetrance, but cannot be passed from affected males.
Classically speaking in regards to mitochondrial inheritance what is the linage of passing the phenotypes?
Affected females pass the disease 100% of the time to their children, while affected males transmit the disease 0% to their children.
What are examples of mitochondrial diseases?
Leber hereditary optic neuropathy (degenerative eye disease) and Leigh Syndrome (LS) (neurological disease with psychomotor regression ).
Also mitochondrial encephalo-myopathy with lactic acidosis and stroke-like episodes (MELAS) and Kearns-Sayre syndrome (KSS)
What is mosaicism and how does it occur?
An individual who's body contains two or more genetically distinct cells. It is caused by mutations post-fertilizations.
When is mosaicism clinically important?
(i) Mutant cells have an increased growth tendency, (ii) mutations occur in embryogenesis and the mutant cell lines makes up a significant amount of the body, (iii) mutations occur in the germline
What are two types of mosaicism and how do they differ?
Germline mosaicism which effects gametes and can be passed down to offspring and somatic mosaicism which affects somatic cells and cannot be passed to offspring.
In order to diagnostically observe that someone has germline mosaicism and somatic mosaicism what would have to be done?
In order to diagnostically observe germline mosaicism germline cells must be biopsied (so sperms cells, eggs, or progenitors. In order to diagnostically observe somatic mosaicism you would have to biopsy the specific somatic cells which if someone had could be potentially in any cells, outside the germline cells, in the body.
If an asymptomatic couple have a child, have tested negative for the mutation, and have a child with a dominant disorder disease any subsequent children will be at _____ risk of being affected by the same disorder.
Increased (as they potentially have a mutation in their germline cells)
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