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Questions and Answers
What physical characteristic is commonly observed in individuals with Klinefelter syndrome?
What physical characteristic is commonly observed in individuals with Klinefelter syndrome?
Which term describes an individual who carries a disease-causing allele but does not exhibit the disease?
Which term describes an individual who carries a disease-causing allele but does not exhibit the disease?
Which mode of inheritance indicates that a single copy of a gene is sufficient to express a trait?
Which mode of inheritance indicates that a single copy of a gene is sufficient to express a trait?
What is the expected occurrence of gynecomastia in individuals with Klinefelter syndrome?
What is the expected occurrence of gynecomastia in individuals with Klinefelter syndrome?
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What defines a polymorphic population regarding alleles?
What defines a polymorphic population regarding alleles?
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What does the principle of independent assortment imply?
What does the principle of independent assortment imply?
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Which of the following is NOT typically seen in Klinefelter syndrome?
Which of the following is NOT typically seen in Klinefelter syndrome?
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What is the locus in genetics?
What is the locus in genetics?
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What role does the proband play in a pedigree chart?
What role does the proband play in a pedigree chart?
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In autosomal dominant inheritance, what percentage of children from a heterozygous affected parent and an unaffected parent is expected to inherit the trait?
In autosomal dominant inheritance, what percentage of children from a heterozygous affected parent and an unaffected parent is expected to inherit the trait?
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Which characteristic is NOT associated with autosomal dominant inheritance?
Which characteristic is NOT associated with autosomal dominant inheritance?
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What does the term 'penetrance' refer to in genetics?
What does the term 'penetrance' refer to in genetics?
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What is the recurrence risk for a child when one parent is heterozygous for an autosomal dominant disease and the other is unaffected?
What is the recurrence risk for a child when one parent is heterozygous for an autosomal dominant disease and the other is unaffected?
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Which condition is an example of age-dependent penetrance?
Which condition is an example of age-dependent penetrance?
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Which of the following is true regarding X-linked recessive disorders?
Which of the following is true regarding X-linked recessive disorders?
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What is true when a child is born with an autosomal dominant disease but there is no family history?
What is true when a child is born with an autosomal dominant disease but there is no family history?
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What defines an obligate carrier?
What defines an obligate carrier?
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Which of the following is true about autosomal recessive inheritance?
Which of the following is true about autosomal recessive inheritance?
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Cystic fibrosis is most common among which population?
Cystic fibrosis is most common among which population?
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Which statement about consanguinity and autosomal recessive diseases is correct?
Which statement about consanguinity and autosomal recessive diseases is correct?
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What is a characteristic of X-linked recessive conditions?
What is a characteristic of X-linked recessive conditions?
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What percentage of offspring from carrier parents are expected to be affected by an autosomal recessive condition?
What percentage of offspring from carrier parents are expected to be affected by an autosomal recessive condition?
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In terms of inheritance pattern, which of the following criteria is NOT typically associated with autosomal recessive diseases?
In terms of inheritance pattern, which of the following criteria is NOT typically associated with autosomal recessive diseases?
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What is the primary consequence of the defective Cl transporter in cystic fibrosis?
What is the primary consequence of the defective Cl transporter in cystic fibrosis?
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In the inheritance of X-linked recessive disorders, how are affected daughters typically impacted by their affected fathers?
In the inheritance of X-linked recessive disorders, how are affected daughters typically impacted by their affected fathers?
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What is the most common mating scenario for the transmission of X-linked recessive disorders?
What is the most common mating scenario for the transmission of X-linked recessive disorders?
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Which of the following statements accurately describes the transmission of X-linked traits?
Which of the following statements accurately describes the transmission of X-linked traits?
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What initiates the process of gonadal differentiation during gestation?
What initiates the process of gonadal differentiation during gestation?
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Which of the following best describes the role of the SRY gene?
Which of the following best describes the role of the SRY gene?
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What factor significantly influences the effectiveness of drug metabolism in individuals?
What factor significantly influences the effectiveness of drug metabolism in individuals?
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Why are some genetic disorders difficult to test for directly?
Why are some genetic disorders difficult to test for directly?
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What is the potential benefit of precision or personalized medicine?
What is the potential benefit of precision or personalized medicine?
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How many Mendelian conditions have had their genetic causes determined?
How many Mendelian conditions have had their genetic causes determined?
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Which term describes a trait that appears more frequently in one sex than the other due to genetic influence?
Which term describes a trait that appears more frequently in one sex than the other due to genetic influence?
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What occurs in triploidy?
What occurs in triploidy?
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Which type of chromosomal abnormality always leads to lethality?
Which type of chromosomal abnormality always leads to lethality?
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What is a common characteristic of Down syndrome?
What is a common characteristic of Down syndrome?
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What genetic condition is most commonly associated with a chromosomal condition involving nondisjunction in maternal age?
What genetic condition is most commonly associated with a chromosomal condition involving nondisjunction in maternal age?
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What effect does a Robertsonian translocation have on chromosomes?
What effect does a Robertsonian translocation have on chromosomes?
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Which disorder is characterized by a female having only one X chromosome?
Which disorder is characterized by a female having only one X chromosome?
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What is often a characteristic result of duplications in chromosomal abnormalities?
What is often a characteristic result of duplications in chromosomal abnormalities?
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Which of the following is a key feature of Fragile X syndrome?
Which of the following is a key feature of Fragile X syndrome?
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How does aneuploidy differ from polyploidy?
How does aneuploidy differ from polyploidy?
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At what point do nearly all triploid conceptions result?
At what point do nearly all triploid conceptions result?
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What is one potential long-term issue faced by individuals with Down syndrome by age 40?
What is one potential long-term issue faced by individuals with Down syndrome by age 40?
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What type of cells can germline mutations be transmitted to?
What type of cells can germline mutations be transmitted to?
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Which of these chromosomal abnormalities involves the rearrangement of genes within chromosomes?
Which of these chromosomal abnormalities involves the rearrangement of genes within chromosomes?
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Which chromosomes are involved in determining sex in humans?
Which chromosomes are involved in determining sex in humans?
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Study Notes
Genes and Genetic Diseases
- This presentation covers genes and genetic diseases.
- Modules include: Guyton chapter 3, McCance chapters 4, 5, and 6.
- Learning objectives include describing gene influence on body structure and function and comparing gene defects to genetic diseases.
- Additional relevant chapters are from McCance chapter 4.
Chromosomes
- Two types of cells: germline and somatic.
- Germline mutations can be passed to the next generation.
- Somatic mutations cannot.
- Diploid cells have 23 pairs of chromosomes.
- 22 pairs are homologous.
- The 23rd pair are sex chromosomes (XX in females, XY in males).
Polyploidy
- Polyploidy occurs when a cell has more than the diploid number of chromosomes (46).
- Several types of body tissue (liver, bronchioles, epithelial) are normally polyploid.
- Triploidy is when a zygote has three copies of each chromosome instead of two.
- Nearly all triploid conceptions are spontaneously aborted or stillborn.
- Accounts for 10% of miscarriages.
Aneuploidy
- Aneuploidy occurs when cells do not contain a multiple of 23 chromosomes.
- Monosomy involves only one copy of a chromosome and is always lethal.
- Trisomy involves three copies of one chromosome.
- Trisomy of chromosomes 13, 18, and 21 can sometimes survive.
- Often a result of non-disjunction (failure of homologous chromosomes or sister chromatids to separate normally during meiosis or mitosis).
Abnormalities of Chromosome Structure
- Parts of chromosomes can be lost, duplicated, or rearranged during gamete formation.
- Deletions: a gamete with a deletion joining with a normal gamete forms a zygote with one chromosome with a normal complement of genes and one missing genes. This can cause serious conditions like Cri du Chat syndrome.
- Duplications are often less harmful.
- Inversions: a breakage in the chromosome followed by reinsertion at the original site, but in inverted order.
- Balanced changes (no loss or gain of genetic material) sometimes cause disease.
- Translocations: the interchanging of genetic material between non-homologous chromosomes.
- Robertsonian translocation: the long arms of two non-homologous chromosomes fuse.
- Reciprocal translocation: breaks take place in different chromosomes and material is exchanged.
- Fragile sites: areas on chromosomes that are prone to breaks and gaps.
- Fragile X syndrome: a fragile site on the X chromosome's long arm, affects approximately 1 in 4000 males and 1 in 8000 females - second most common genetic cause of intellectual disability after Down syndrome.
Down Syndrome
- The most well-known example of aneuploidy chromosomal cells.
- Approximately 10 in 800 live births.
- Typically have low IQ quotients.
- Risk increases with maternal age.
- Facial appearance is distinctive.
- Often develop symptoms nearly identical to Alzheimer's disease by 40 years of age.
- One gene that causes Alzheimer's is located on chromosome 21.
Turner Syndrome
- One of the most common single chromosome aberrations – 15–20% of spontaneous abortions.
- One in 2500 newborn females is affected.
- Single X chromosome (total of 45 chromosomes).
- Always female, typically sterile.
- Physical characteristics include short stature, webbing of the neck, widely spaced nipples, aorta coarctation, and edema of the feet in newborns.
Klinefelter Syndrome
- Two X and one Y chromosome.
- Male appearance, but usually sterile.
- Physical characteristics include gynecomastia (breast development), small testes, sparse body hair, elevated stature, and a somewhat high-pitched voice.
- Often have a moderate degree of mental impairment.
- About 1 in 1000 male births.
Elements of Formal Genetics
- Locus: Location of a gene on a chromosome.
- Alleles: Different forms of a gene at a particular locus.
- Polymorphic: When two or more alleles occur frequently in a population.
- Genotype: Genetic makeup of an organism.
- Phenotype: Observable characteristics of an organism.
- Dominant allele.
- Recessive allele.
- Carrier: Individual with a disease-causing allele but is phenotypically normal.
Transmission of Genetic Diseases
- Mode of inheritance: The pattern in which a disease is inherited through generations.
- Mendelian traits: Patterns discovered by Gregor Mendel; Principal of segregation (genes separate during reproduction) and Principal of independent assortment (hereditary transmission of one gene does not affect another).
- Autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive are the four major modes of inheritance.
Pedigree Chart
- Summarizes family relationships and shows which individuals are affected by a genetic disease
- Proband / Propositus is the affected individual diagnosed or seen in a clinic
- Uses symbols to represent different family relationships and affection status (normal, carrier, affected etc.).
Autosomal Dominant Inheritance
- Both sexes are equally affected.
- No skipping generations.
- Affected heterozygotes transmit the trait in approximately 50% of their children.
- Two affected individuals may produce offspring together that are also affected.
Genetic Disease Characteristics
- Recurrence risk: Probability a child will inherit the disease, usually 50% when one parent is heterozygous affected and the other is not affected.
- New mutation: Children born with autosomal dominant disease without family history of disease are likely a result of a new mutation.
- Penetrance: Percentage of individuals with a particular genotype who also exhibit the expected phenotype.
- Incomplete penetrance: Disease-causing allele may not always manifest.
- Age-dependent penetrance: Symptoms may be delayed until later in life.
Autosomal Recessive Inheritance
- Rare diseases caused by autosomal recessive alleles
- Carrier frequency can be high
- Individuals must be homozygous for recessive allele to express the disease.
- Individuals usually show no symptoms or signs of disease (carrier).
- Characterized by incomplete penetrance and variable expressivity.
- Cystic fibrosis: Most common lethal recessive disease in white children (approximately 1 in 2500 births).
- Death from lung disease or heart failure at approximately age 40.
X-linked Inheritance
- Mostly located on the X chromosome, with few on the Y.
- Males receive one X chromosome from their mother and this determines if a trait occurs.
- Females need two copies of the recessive allele to express the X-linked disease, whereas males only need one copy.
- Males are more commonly affected by X-linked recessive diseases.
- X-linked recessive is passed through a series of carrier female generations.
- Affected fathers transmit the trait to all daughters who will be carriers but won't likely show signs of the trait. Affected fathers will transmit to approximately half of their sons, who will be affected.
- Duchenne muscular dystrophy (DMD) is a severe X-linked recessive disorder.
X-linked Recurrence Risk
- Most common mating type is a carrier female and a normal male.
- The mother will transmit the disease causing allele to half of their offspring.
- Half the daughters will be carriers, half will be normal.
- Half the sons will be normal, half will have the disease.
Sex Determination
- Begins during the sixth week of gestation.
- One Y chromosome is sufficient to initiate gonadal differentiation.
- The number of X chromosomes doesn't affect the sex determination process.
- The SRY (Sex determining region on the Y) gene triggers the action of genes on other chromosomes, making the individual male.
Sex-linked Traits
- Sex-limited trait: A trait that occurs in only one sex, often due to anatomic differences.
- Sex-influenced trait: A trait that occurs more often in one sex than the other (e.g., male-pattern baldness).
Gene Identification
- Locating gene positions on chromosomes is key to understanding genetic diseases.
- Sequencing the whole human genome is now more common to find disease-causing mutations.
- This allows for more accurate diagnoses and, potentially, more effective treatments.
Precision or Personalized Medicine
- Takes into account each person's unique genetic and environmental risk factors.
- Diagnosis of disease by searching for disease-causing chromosome variations.
- Genetic testing can help in guiding therapeutic drug prescription.
- Variation in genes like CYP2D6 influences how drugs are metabolized.
- Testing for CYP2D6 helps in estimating appropriate drug levels.
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Description
This quiz explores the concepts of genes, genetic diseases, and their influence on body structure and function. It covers key modules from Guyton's chapter 3 and McCance's chapters 4, 5, and 6, delving into germline and somatic cells, mutations, and polyploidy. Enhance your understanding of hereditary conditions and their biological impacts.
