75 Questions
What is a characteristic feature of chimerism in humans?
Fusion of two zygotes forms a single embryo
How is chimerism typically proven?
By the presence of too many parental alleles at several loci
What is the distinguishing feature of XX/XY chimerism?
The presence of both XX and XY cells in the same individual
What is the result of the fusion of two embryos after in vitro fertilization?
A chimera with two sets of cells
What is the term for the colonization of one twin by cells from a non-identical co-twin?
Limited colonization
What is the term for the mixing of two cell lines, one XX and one XY, in a single individual?
Chimerism
What is the likely consequence of a gain of function mutation in a cell surface receptor?
The cell responds as if the signaling compound is continuously present
What is the underlying genetic mechanism leading to Jansen's disease?
Gain of function mutation in the parathyroid hormone receptor gene
What is the consequence of duplication of the PMP22 gene?
Recombination between repeat sequences on chromosome 17
Which of the following is NOT a characteristic of trinucleotide repeat expansions?
Results in growth defects
What is the mechanism by which a mutation in a cell surface receptor can lead to a gain of function?
The receptor becomes constitutively active in the absence of the signaling compound
What is the name of the inherited disorder caused by a trinucleotide repeat expansion in the Huntingtin gene?
Huntington's disease
What is the characteristic of a locus with paternal expression and maternal silencing?
It is an example of genomic imprinting
What is the term for the presence of two or more genetically different sets of cells in an individual's body?
Mosaicism
What type of mutation is NOT associated with the syndromes mentioned in the text?
Gain of function mutation
What is the characteristic of an individual with Mosaic Down syndrome?
They have some cells with 46 chromosomes and others with a different number of chromosomes
What is the normal range of repetition of the sequence 5’-CAG-3’ in the HD gene?
6-35 times
What is the effect of the expansion of the CAG repeat in Huntington’s disease?
It results in a loss of function of the HD protein
What is the role of the HD protein in the nerve cells of the brain?
Its biochemical role is not yet discovered
What is a characteristic of dominant inherited diseases?
They can be inherited from either parent
What is a characteristic of Huntington’s disease?
It is a dominant inherited disease
Why do many dominant inherited diseases have incomplete penetrance or delayed onset?
Because they are not severe enough to prevent reproduction
What is an example of a dominant inherited disease?
Huntington’s disease
What is the result of the expansion of the CAG repeat in the Huntingtin gene?
A loss of function of the HD protein
What is the term used to describe traits that are influenced by multiple genes?
Polygenic
What is the leading cause of death worldwide?
Heart disease
What is the most common underlying cause of heart disease?
Coronary artery disease
What is atherosclerosis?
A narrowing of the coronary arteries
What is a common consequence of atherosclerosis in the arteries that supply blood to the brain?
Stroke
What is a risk factor for coronary artery disease?
Elevated cholesterol level
What is the result of inadequate supply of oxygen to the heart tissue?
Myocardial infarction
What is the term used to describe traits that are influenced by multiple genes and environmental factors?
Multifactorial
What determines the threshold for phenotypic expression of mitochondrial gene mutations?
Energy requirements of the cell or tissue
Which tissue has considerable energy requirements and is highly susceptible to mitochondrial gene mutations?
Brain
What is the incidence of mitochondrial disorders in live births?
1 in 10,000
What is an indication of a non-Mendelian process in mitochondrial genetics?
Lack of phenotypic equivalence from reciprocal matings
What is a biological consequence of mitochondrial mutations?
Myopathy
Why are cells with low energy requirements less affected by homoplasmy for mutant mitochondrial DNA?
They have lower energy requirements
What is the result of the combination of mitochondrial mutations and high energy requirements?
Increased risk of disease
Which organs are highly susceptible to mitochondrial gene mutations due to their high energy requirements?
Brain and skeletal muscles
What is the chromosome associated with Prader-Willi and Angelman syndromes?
15q
What is the term for the presence of two or more cell types or lines in an individual, resulting from an error during mitosis?
Mosaicism
What is a characteristic of a person with Mosaicism?
Some cells have 46 chromosomes, while others have a different number of chromosomes
Which of the following syndromes is associated with paternal deletion and obesity?
Prader-Willi syndrome
What is the role of genomic imprinting in the inheritance of certain syndromes?
It prevents the expression of certain genes
How many human genes are known to be imprinted?
At least 80
What is the characteristic of Angelman syndrome?
All of the above
What is the result of mosaicism in an individual?
Both A and B
What is the main difference between a chimera and a mosaic?
The number of fertilized eggs involved
What is the result of limited colonization of one twin by cells from a non-identical co-twin?
Chimerism
How do blood-grouping centers occasionally discover chimeras?
Among normal donors
What is the term for the fusion of two embryos after in vitro fertilization?
Embryo amalgamation
What is the characteristic of the 46,XY/46,XX boy described in the study by Strain et al.?
He is a chimera
What is the main difference between a chimera and a Greek mythological creature?
The physical characteristics
What is a chimera in Greek mythology?
A fire-breathing creature with physical traits of a lion, goat, and dragon
What is the result of fusion of two zygotes to form a single embryo?
Chimerism
What is a characteristic of an XX/XY chimera?
Presence of two cell lines, one 46,XX and the other 46,XY
What is the name of the study that described a 46,XY/46,XX boy?
Strain et al.
What is the result of in vitro fertilization in which three embryos were transferred into the mother’s uterus?
Chimerism
What is the term used to describe the colonization of one twin by cells from a non-identical co-twin?
Limited colonization of one twin by cells from a non-identical co-twin
What is the term used to describe a single embryo that develops from the fusion of two zygotes?
Chimerism
What is a characteristic of blood-grouping centers?
Discovery of chimeras among normal donors
What is the most favored explanation for families with autosomal dominant disorders where parents are phenotypically normal but their children are affected?
Gonadal mosaicism in one of the parents
Which of the following disorders is an example of an X-linked recessive disorder?
Duchenne muscular dystrophy
What is the term for the presence of two or more genetically different sets of cells in an individual's body?
Chimerism
What is the characteristic of families with X-linked recessive disorders where parents are phenotypically normal but their children are affected?
Gonadal mosaicism in one of the parents
What is a characteristic feature of Bardet-Biedl syndrome (BBS)?
All of the above
What is the minimum number of mutant alleles required to give rise to the BBS phenotype in some cases?
3
Which of the following is NOT a clinical feature of Bardet-Biedl syndrome (BBS)?
Heart defects
What is the pattern of inheritance of Bardet-Biedl syndrome (BBS)?
Autosomal recessive
How many loci have been identified for Bardet-Biedl syndrome?
At least eight
What is a characteristic of Bardet-Biedl syndrome?
A combination of retinal dystrophy, obesity, polydactyly, kidney defects, underdeveloped testes, and cognitive impairment
What is required to give rise to the Bardet-Biedl syndrome phenotype in some cases?
Three mutant alleles at the BBS2 and BBS6 loci
What is the term for Bardet-Biedl syndrome?
A heterogeneous recessive disorder
What are the possible consequences of having multiple mutant alleles at the BBS2 and BBS6 loci?
The Bardet-Biedl syndrome phenotype
Study Notes
• Multifactorial diseases are caused by the combined effects of multiple genes and environmental factors, and include heart disease, which is the leading cause of death worldwide, accounting for approximately 25% of all deaths in the United States.
• Heart disease is often caused by coronary artery disease (CAD), which is a result of atherosclerosis, a narrowing of the coronary arteries due to the formation of lipid-laden lesions, impeding blood flow to the heart and potentially leading to a myocardial infarction.
• Risk factors for CAD include obesity, cigarette smoking, hypertension, elevated cholesterol levels, and a positive family history, usually defined as having one or more affected first-degree relatives.
• Genomic imprinting is a phenomenon where the expression of a gene depends on its parental origin, with at least 80 human genes known to be imprinted, including those involved in Prader-Willi and Angelman syndromes, and Beckwith-Wiedemann and Russell-Silver syndromes.
• Mosaicism occurs when an individual or a particular tissue consists of more than one cell type or line, resulting from an error during mitosis, and can account for unusual patterns of inheritance or phenotypic features in an affected individual.
• Huntington's disease is a dominant inherited disease caused by an expansion of a repeat sequence in the HD gene, leading to a loss of function of the HD protein, which is thought to act within the nerve cells of the brain.
• Mitochondrial diseases are caused by mutations in mitochondrial DNA and can result in a range of symptoms, including myopathy, cardiomyopathy, dementia, and loss of cerebral blood supply, with an incidence of about 1 in 10,000 live births.
• Chimerism is a rare phenomenon where a single individual is composed of cells from two or more fertilized eggs, which can be detected by the presence of multiple parental alleles at several loci.
• A chimera can result from the fusion of two zygotes to form a single embryo, or the colonization of one twin by cells from a non-identical co-twin, and can be proven by karyotyping of peripheral-blood lymphocytes.
• Cystic fibrosis is an autosomal recessive disorder affecting approximately 8000 people in the UK and 30,000 in the USA, caused by any one of 1400 different mutations, which can affect the body's cells, tissues, and glands, leading to faulty mucus and sweat production.
• Bardet-Biedl syndrome is a multifactorial disease that is thought to be caused by the combined effects of multiple genes, with at least 12 different genes implicated in the disorder.
Test your knowledge of genetics and cell biology with this quiz, covering topics such as gene duplication, mutation, and cell signaling. Learn about the effects of genetic changes on cell function and more.
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