Genetics

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary role of a pedigree chart in genetic studies?

To establish the age of genetic mutations

To summarize family relationships and identify affected individuals (correct)

To predict the probability of disease recurrence

To map the location of disease-causing genes

Which of the following statements is TRUE regarding autosomal dominant inheritance?

Both sexes are affected in unequal proportions

Affected individuals transmit the trait to about 50% of their offspring (correct)

Homozygous affected individuals are commonly observed

The trait skips generations frequently

What does penetrance refer to in genetics?

The number of individuals affected by a genetic disease

The percentage of individuals with a genotype that exhibit the expected phenotype (correct)

The age at which symptoms of a disease appear

The chance that a child will inherit a genetic disease

What is the recurrence risk for a child if one parent is heterozygous affected and the other is unaffected within autosomal dominant inheritance?

50% Signup and view all the answers

In incomplete penetrance, what can occur even if an individual has a disease-causing allele?

They may not exhibit the disease phenotype at all Signup and view all the answers

What phenomenon can cause a child to be born with an autosomal dominant disease in families with no prior history of the disease?

New mutation Signup and view all the answers

Which of these terms refers to the first person diagnosed with a genetic disease in a family?

Propositus/Proposita Signup and view all the answers

Which of the following is NOT a characteristic of autosomal dominant inheritance?

Affected individuals can skip generations Signup and view all the answers

Which physical characteristic is commonly associated with Klinefelter syndrome?

Gynecomastia Signup and view all the answers

What is the definition of a genotype?

The composition of genes at a given locus Signup and view all the answers

In formal genetics, what does the term 'polymorphic' refer to?

Two or more alleles occurring with appreciable frequencies in a population Signup and view all the answers

What is the principal of segregation in genetics?

Homologous genes separate so that each reproductive cell carries one allele. Signup and view all the answers

What is a common consequence for individuals with Klinefelter syndrome?

Infertility due to non-functional testes Signup and view all the answers

Which mode of inheritance involves traits that are expressed in the presence of just one dominant allele?

Autosomal dominant Signup and view all the answers

What does it mean for a genotype to be considered a carrier?

The genotype has one disease-causing allele but is phenotypically normal. Signup and view all the answers

Which characteristic is NOT commonly associated with Klinefelter syndrome?

Large testicular size Signup and view all the answers

What is an obligate carrier?

An individual who must carry the recessive allele due to affected parents and children Signup and view all the answers

What characterizes diseases caused by autosomal recessive alleles?

They are typically expressed only in homozygous individuals Signup and view all the answers

Which statement is true regarding the most common lethal recessive disease in white children?

Cystic fibrosis leads to thick mucus secretions due to a salt imbalance Signup and view all the answers

What is a contributing factor to the occurrence of autosomal recessive diseases in a population?

Consanguinity among related individuals Signup and view all the answers

Which characteristic is common to both autosomal recessive and autosomal dominant diseases?

Phenotypic normality in carriers of the disease Signup and view all the answers

Why are males more frequently affected by X-linked recessive diseases?

Females have two X chromosomes which compensate for the recessive alleles Signup and view all the answers

What is one of the criteria for discerning autosomal recessive inheritance?

Approximately 25% of offspring from carrier parents will be affected Signup and view all the answers

What distinguishes X-linked traits from autosomal traits?

X-linked traits often have a higher incidence in males due to their single X chromosome Signup and view all the answers

In X-linked recessive disorders, how do males inherit the disease compared to females?

Males only need one recessive allele inherited from their mother. Signup and view all the answers

Which of the following statements is true regarding the transmission of X-linked traits?

The gene can skip generations through carrier females. Signup and view all the answers

What initiates the process of gonadal differentiation during gestation?

The presence of a Y chromosome. Signup and view all the answers

What is a sex-influenced trait?

A trait that occurs much more frequently in one sex. Signup and view all the answers

What is the significance of the CYP2D6 gene in precision medicine?

It influences the metabolism of over 25% of all prescribed drugs. Signup and view all the answers

During genetic testing for diseases, what is often analyzed?

The entire germline DNA sequence. Signup and view all the answers

In the most common mating scenario involving an X-linked disorder, what can be expected?

Half of the daughters will be normal, and half will be carriers. Signup and view all the answers

Which of the following is considered the most common and severe X-linked recessive disorder?

Duchenne muscular dystrophy (DMD) Signup and view all the answers

What does precision medicine take into account for disease management?

Environmental and genetic risk factors. Signup and view all the answers

How can genetic testing enhance drug therapy outcomes?

By providing specific recommendations for drug administration and dosing. Signup and view all the answers

What type of cells have mutations that can be transmitted to the next generation?

Germline cells Signup and view all the answers

Which of the following describes triploidy?

A zygote has three copies of each chromosome. Signup and view all the answers

What type of aneuploidy is characterized by having only one copy of a specific chromosome?

Monosomy Signup and view all the answers

Which chromosome abnormality involves losing a part of a chromosome?

Deletion Signup and view all the answers

What occurs during a reciprocal translocation?

Material is exchanged between two non-homologous chromosomes. Signup and view all the answers

What is a hallmark physical characteristic of Down syndrome?

Protruding tongue Signup and view all the answers

Which of the following is a common consequence of Turner syndrome?

Reduction in the number of chromosomes to 45 Signup and view all the answers

How are fragile sites on chromosomes usually described?

Areas that develop observable breaks and gaps Signup and view all the answers

What is a characteristic of trisomic cells?

They contain three copies of one chromosome. Signup and view all the answers

What is typically associated with Cri du chat syndrome?

A deletion of part of chromosome 5 Signup and view all the answers

What percentage of Down syndrome cases are due to translocations?

3% Signup and view all the answers

What is usually the result of aneuploidy caused by non-disjunction?

Abnormal number of chromosomes Signup and view all the answers

What is the probability of Down syndrome occurring with increasing maternal age?

Increases significantly Signup and view all the answers

Study Notes

Genes and Genetic Diseases

Genes influence all aspects of body structure and function.
Defects in genes can lead to recognizable genetic diseases.
Learning objectives include describing gene influence and comparing gene defects leading to genetic diseases.

Chromosomes

Two types of cells:
- Germline: Mutations can be transmitted to the next generation.
- Somatic: Diploid cells with 23 pairs of chromosomes.
Homologous chromosomes: 22 pairs are virtually identical.
Sex chromosomes: 1 pair, X in females, X and Y in males.

Polyploidy

A germ line or somatic cell with more than the diploid number (46) of chromosomes.
Several types of body tissue (liver, bronchioles, epithelial) are normally polyploid.
Triploidy: 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

Cells that do not contain a multiple of 23 chromosomes.
Monosomy: A diploid cell with only one copy of a given chromosome. (Always lethal)
Trisomy: An aneuploid cell with three copies of one chromosome. (Trisomy of 13, 18, and 21 can survive)
Results from non-disjunction of homologous chromosomes or sister chromatids during meiosis or mitosis.

Abnormalities of Chromosome Structure

Parts of chromosomes can be lost or duplicated as gametes are formed.
Deletions: One chromosome with a normal complement of genes and one with missing genes.
Cri du chat syndrome: Duplications usually have less serious consequences than deficiencies.
Inversions: The occurrence of two breaks on a chromosome, followed by reinsertion in an inverted order.
"Balanced" abnormalities: No loss or gain of genetic material.
Translocations: Interchange of genetic material between non-homologous chromosomes.
Robertsonian translocation: Long arms of two non homologous chromosomes fuse;
Reciprocal translocation: Breaks take place in different chromosomes and the material is exchanged.
Fragile sites: Areas on chromosomes with observable breaks/gaps, but the majority have no relation to disease (some exceptions like fragile X syndrome)

Down Syndrome

The most well-known example of aneuploidy chromosomal cells.
10 in 800 live births.
Typically have low IQ quotients.
Risk greatly increases with maternal age.
Approximately 97% caused by nondisjunction during gamete formation.
Remaining 3% result from translocations.
Distinctive facial appearance (low nasal bridge, epicanthal folds, large tongue, flat low-set ears).
Congenital heart defects occur in 1/3 to 2/3 of cases.
Significant symptoms of Alzheimer's disease develop around age 40.
One of the genes that can cause Alzheimer’s is located on chromosome 21.

Turner Syndrome

One of the most common single chromosome aberrations.
15 to 20% of spontaneous abortions.
One in 2500 newborn females is affected.
Presence of a single X chromosome results in a total of 45 chromosomes.
Affected individuals are always female, but typically sterile.
Physical characteristics: Short stature, webbing of the neck, widely spaced nipples, coarctation of the aorta(15-20%), edema of the feet in newborns, sparse body hair.

Klinefelter Syndrome

2 X chromosomes and a Y chromosome.
Due to the presence of a Y chromosome, affected individuals have a male appearance, but usually sterile.
Physical characteristics: 50% develop gynecomastia, small testes, sparse body hair, tall stature, somewhat high-pitched voice.
Moderate degree of mental impairment is often present.
About 1 in 1000 male births.

Elements of Formal Genetics

Locus: The location each gene occupies on a chromosome.
Alleles: Genes at a particular locus can take different forms. (example: hemoglobin S or hemoglobin A).
Polymorphic: When two or more alleles each occur with appreciable frequencies in a population.
Genotype: The composition of genes at a given locus.
Phenotype: The result of both genotype and environment.
Dominant allele: The allele whose affects mask another on a heterozygote.
Recessive allele: To be expressed, it must exist in a homozygote form.
Carrier: An individual who has 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 of a family.
Mendelian traits (after Gregor Mendel).
Principal of Segregation: Homologous genes separate during reproduction; each reproductive cell carries only one of the homologous genes.
Principle of independent assortment: Hereditary transmission of one gene has no effect on the transmission of another.
Known single-gene diseases can be classified in the following major modes of inheritance:
- Autosomal dominant
- Autosomal recessive
- X-linked dominant
- X-linked recessive
Pedigree chart: Summarizes family relationships and shows which individuals are affected by a genetic disease. Proband/propositus is the individual diagnosed.

Autosomal Dominant Inheritance

Both sexes exhibit the trait in equal proportion.
No skipping generations.
Affected heterozygous individuals transmit the trait to approximately 50% of their children.

Genetic Disease Characteristics

Recurrence risk: The chance a child will have a disease when one parent is heterozygous affected.
If a child has an autosomal dominant disease without a family history, it is likely a new mutation.
Penetrance: The percentage of individuals with a genotype who also exhibit the expected phenotype.
Incomplete penetrance: Individuals with the disease-causing allele might not exhibit the disease phenotype.
Age-dependent penetrance: Disease symptoms might not appear until a certain age.(example: breast cancer)

Autosomal Recessive Inheritance

Diseases caused by autosomal recessive alleles are rare.
Individuals must be homozygous for the recessive allele to express the disease.
Carries are phenotypically normal.
Characteristic of incomplete or age-dependent penetrance and variable expressivity
Examples include cystic fibrosis.

X-linked Inheritance

Most sex-linked traits are located on the X chromosome, except for some fragile X syndrome traits.
Females receive two X chromosomes (can be homozygous for disease, homozygous for normal allele or heterozygous).
Males inherit a recessive disease on the X chromosome and will be affected because the Y chromosome does not carry a normal allele.
Males are more frequently affected by X-linked recessive diseases.

Characteristics of X-linked Recessive Conditions

X-linked recessive conditions generally affect males more than females.
Traits are often seen in every generation
Affected fathers will transmit to all daughters who then will be phenotypically normal carriers.
Example: Duchene muscular dystrophy (DMD)
X-linked recurrence risk: The affected mother can pass the disease-causing allele to approximately half of her offspring; half of the daughters will be carriers, and half of the sons will be affected if the father is normal.

Sex Determination

Begins during the sixth week of gestation.
One Y chromosome is sufficient to initiate gonadal differentiation.
The number of X chromosomes does not affect this process.
SRY (Sex determining region on the Y) on the short arm of the Y chromosome acts as a trigger for gene action on other chromosomes. Sex-linked traits occur in only one sex because of anatomic differences, and sex-influenced traits appear disproportionately in one sex.

Gene Identification

Locating gene positions on chromosomes is a crucial endeavor in human genetics.
For most genetic diseases, direct testing for the disease-causing mutation might not be possible.
Whole genome sequencing has become a more accessible and cost-effective way to search for disease-causing mutations in individuals or families.

Precision or Personalized Medicine

Each person's unique genetic and environmental factors influence disease diagnosis and management.
Genetic testing is becoming increasingly common for diagnosing diseases and guiding therapeutic drug prescription.
Variance in genes like CYP2D6 impact drug metabolism and dosing recommendations, requiring personalized strategies.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.