2025/2026 Nightingale College: SCI225-22 Pathophysiology
1. Heterozygous - Definition:
A genetic condition where an individual has two ditterent alleles for a particular
gene.
- Pathophysiology:
This condition occurs when an individual inherits one dominant allele and one
recessive allele for a specific gene, leading to expression of the dominant allele.
- Example:
A common example is the presence of one normal hemoglobin allele and one
sickle cell allele, leading to the expression of sickle cell trait.
- Clinical significance: individuals are often carriers of a genetic condition and can
pass it on to their ottspring. The phenotype of a heterozygous individual may also
be intermediate between the two homozygous conditions.
2. Homozygous - Definition:
an individual who inherits the same pair of genes for a particular trait from both
parents.
- Pathophysiology:
The genetic material of an individual is comprised of chromosomes which carry
genes.
A gene can have ditterent forms, called alleles, that determine a specific trait, such
as eye color.
When an individual inherits two copies of the same allele from both parents, they
are homozygous for that trait.
Homozygous individuals are typically more predictable in their traits than het-
erozygous individuals.
- Clinical Significance:
individuals play a crucial role in genetic studies, as their genetic makeup allows
for more definitive conclusions about the ettect of a particular gene on a particular
trait.
Homozygosity can also increase the risk of certain genetic disorders when a
person inherits two copies of a gene that causes a disease.
, 2025/2026 Nightingale College: SCI225-22 Pathophysiology
- Scientific Information:
can be described as either complete (having two identical copies of a gene) or
incomplete (having two slightly ditterent copies of a gene).
The frequency of homozygosity in a population can attect the incidence of genetic
disorders.
Homozygosity mapping is a technique used to identify the specific genes respon-
sible for inherited disorders by comparing the DNA of attected and unattected
individuals who are homozygous for a particular region of the genome.
3. Genotype - Definition:
The genetic makeup of an organism, represented by the combination of genes it
carries, which determines its inherited traits.
- Pathophysiology:
determined by its DNA and is passed down from its parents. The genes in the DNA
code for specific traits, and variations in the DNA sequence can result in ditterent
traits or susceptibility to certain diseases.
- Clinical significance: important in genetics, medicine, and biotechnology, as it
can provide information about a person's inherited traits, predisposition to certain
diseases, and potential responses to medications.
- Note: can be influenced by environmental factors such as diet, lifestyle, and
exposure to toxins. The observable traits of an organism, including physical,
behavioral, and metabolic characteristics, are referred to as its phenotype.
4. Phenotype - Definition:
The observable characteristics of an individual, resulting from the interaction
between the individual's genetic makeup and environmental factors.
- Factors:
l is determined by the combination of genes they inherit from their parents, as
well as environmental factors such as diet, lifestyle, and exposure to toxins.
- Importance: can provide valuable information about their health and suscepti-
bility to certain diseases, and can inform medical treatment and management.
, 2025/2026 Nightingale College: SCI225-22 Pathophysiology
- Example:
For example, may indicate that they are at increased risk for certain cancers or
cardiovascular disease due to a family history of these conditions, or may reflect
the presence of a genetic mutation that is associated with a particular disease.
5. Allele - Medical/Scientific Definition:
- a variant form of a gene that is located at the same position on a chromosome
as another gene.
- Clinical Significance:
- can determine ditterences in physical traits, such as eye color or blood type.
- There are dominant and recessive, and the expression of a trait is determined
by which allele is dominant.
- Some alleles can also increase the risk of genetic disorders, such as cystic fibrosis
or sickle cell anemia.
- Pathophysiology:
-The pathophysiology of a genetic disorder caused by these can occur when
mutations change the structure or function of the protein produced by the gene.
-If a dominant carries a mutation, it can suppress the normal function of the
recessive allele, leading to a genetic disorder.
-If a recessive carries a mutation, a person will only develop the disorder if they
inherit two copies of the mutated allele.
6. Klinefelter syn- - Definition:
drome A genetic disorder characterized by the presence of an extra X chromosome in a
male's karyotype, leading to a 47,XXY genotype
- Prevalence: Occurs in 1 in 500-1,000 live male births
- Clinical features: Small testes, reduced sperm count, infertility, gynecomastia, tall
stature, speech and language diflculties, and an increased risk for breast cancer
Pathophysiology: The extra X chromosome interferes with normal testicular devel-
opment, leading to reduced production of testosterone and infertility
- Diagnosis: Karyotype analysis or genetic testing
, 2025/2026 Nightingale College: SCI225-22 Pathophysiology
- Treatment: Hormone replacement therapy (testosterone), speech therapy, and
other therapies based on the symptoms.
- Note: is a common cause of male infertility and is often underdiagnosed. Early
recognition and treatment can help improve symptoms and quality of life.
7. Down syndrome - Definition:
Chromosomal disorder resulting from the presence of an extra copy of chromo-
some 21.
- Etiology:
Most commonly caused by a nondisjunction event in meiosis, leading to a fertil-
ized egg with 3 copies of chromosome 21 instead of the normal 2.
- Signs and Symptoms:
- Delays in physical and intellectual development
- Low muscle tone
- Facial features such as upward slanting eyes, small ears, and a flat nasal bridge
- Short stature
- Cognitive impairment ranging from mild to moderate
- Increased risk for heart defects, hearing and vision problems, respiratory infec-
tions, and thyroid problems.
- Diagnosis:
Antenatal screening and diagnostic testing (ultrasound, amniocentesis, chorionic
villus sampling)
Newborn physical examination and genetic testing (chromosomal analysis)
- Treatment:
Multidisciplinary care involving medical, educational, and social support to help
individuals with Down syndrome reach their full potential.
Treatment for specific medical conditions may be necessary.
- Prognosis:
Life expectancy has improved over the years and many individuals lead healthy
and fulfilling lives with appropriate support.
1. Heterozygous - Definition:
A genetic condition where an individual has two ditterent alleles for a particular
gene.
- Pathophysiology:
This condition occurs when an individual inherits one dominant allele and one
recessive allele for a specific gene, leading to expression of the dominant allele.
- Example:
A common example is the presence of one normal hemoglobin allele and one
sickle cell allele, leading to the expression of sickle cell trait.
- Clinical significance: individuals are often carriers of a genetic condition and can
pass it on to their ottspring. The phenotype of a heterozygous individual may also
be intermediate between the two homozygous conditions.
2. Homozygous - Definition:
an individual who inherits the same pair of genes for a particular trait from both
parents.
- Pathophysiology:
The genetic material of an individual is comprised of chromosomes which carry
genes.
A gene can have ditterent forms, called alleles, that determine a specific trait, such
as eye color.
When an individual inherits two copies of the same allele from both parents, they
are homozygous for that trait.
Homozygous individuals are typically more predictable in their traits than het-
erozygous individuals.
- Clinical Significance:
individuals play a crucial role in genetic studies, as their genetic makeup allows
for more definitive conclusions about the ettect of a particular gene on a particular
trait.
Homozygosity can also increase the risk of certain genetic disorders when a
person inherits two copies of a gene that causes a disease.
, 2025/2026 Nightingale College: SCI225-22 Pathophysiology
- Scientific Information:
can be described as either complete (having two identical copies of a gene) or
incomplete (having two slightly ditterent copies of a gene).
The frequency of homozygosity in a population can attect the incidence of genetic
disorders.
Homozygosity mapping is a technique used to identify the specific genes respon-
sible for inherited disorders by comparing the DNA of attected and unattected
individuals who are homozygous for a particular region of the genome.
3. Genotype - Definition:
The genetic makeup of an organism, represented by the combination of genes it
carries, which determines its inherited traits.
- Pathophysiology:
determined by its DNA and is passed down from its parents. The genes in the DNA
code for specific traits, and variations in the DNA sequence can result in ditterent
traits or susceptibility to certain diseases.
- Clinical significance: important in genetics, medicine, and biotechnology, as it
can provide information about a person's inherited traits, predisposition to certain
diseases, and potential responses to medications.
- Note: can be influenced by environmental factors such as diet, lifestyle, and
exposure to toxins. The observable traits of an organism, including physical,
behavioral, and metabolic characteristics, are referred to as its phenotype.
4. Phenotype - Definition:
The observable characteristics of an individual, resulting from the interaction
between the individual's genetic makeup and environmental factors.
- Factors:
l is determined by the combination of genes they inherit from their parents, as
well as environmental factors such as diet, lifestyle, and exposure to toxins.
- Importance: can provide valuable information about their health and suscepti-
bility to certain diseases, and can inform medical treatment and management.
, 2025/2026 Nightingale College: SCI225-22 Pathophysiology
- Example:
For example, may indicate that they are at increased risk for certain cancers or
cardiovascular disease due to a family history of these conditions, or may reflect
the presence of a genetic mutation that is associated with a particular disease.
5. Allele - Medical/Scientific Definition:
- a variant form of a gene that is located at the same position on a chromosome
as another gene.
- Clinical Significance:
- can determine ditterences in physical traits, such as eye color or blood type.
- There are dominant and recessive, and the expression of a trait is determined
by which allele is dominant.
- Some alleles can also increase the risk of genetic disorders, such as cystic fibrosis
or sickle cell anemia.
- Pathophysiology:
-The pathophysiology of a genetic disorder caused by these can occur when
mutations change the structure or function of the protein produced by the gene.
-If a dominant carries a mutation, it can suppress the normal function of the
recessive allele, leading to a genetic disorder.
-If a recessive carries a mutation, a person will only develop the disorder if they
inherit two copies of the mutated allele.
6. Klinefelter syn- - Definition:
drome A genetic disorder characterized by the presence of an extra X chromosome in a
male's karyotype, leading to a 47,XXY genotype
- Prevalence: Occurs in 1 in 500-1,000 live male births
- Clinical features: Small testes, reduced sperm count, infertility, gynecomastia, tall
stature, speech and language diflculties, and an increased risk for breast cancer
Pathophysiology: The extra X chromosome interferes with normal testicular devel-
opment, leading to reduced production of testosterone and infertility
- Diagnosis: Karyotype analysis or genetic testing
, 2025/2026 Nightingale College: SCI225-22 Pathophysiology
- Treatment: Hormone replacement therapy (testosterone), speech therapy, and
other therapies based on the symptoms.
- Note: is a common cause of male infertility and is often underdiagnosed. Early
recognition and treatment can help improve symptoms and quality of life.
7. Down syndrome - Definition:
Chromosomal disorder resulting from the presence of an extra copy of chromo-
some 21.
- Etiology:
Most commonly caused by a nondisjunction event in meiosis, leading to a fertil-
ized egg with 3 copies of chromosome 21 instead of the normal 2.
- Signs and Symptoms:
- Delays in physical and intellectual development
- Low muscle tone
- Facial features such as upward slanting eyes, small ears, and a flat nasal bridge
- Short stature
- Cognitive impairment ranging from mild to moderate
- Increased risk for heart defects, hearing and vision problems, respiratory infec-
tions, and thyroid problems.
- Diagnosis:
Antenatal screening and diagnostic testing (ultrasound, amniocentesis, chorionic
villus sampling)
Newborn physical examination and genetic testing (chromosomal analysis)
- Treatment:
Multidisciplinary care involving medical, educational, and social support to help
individuals with Down syndrome reach their full potential.
Treatment for specific medical conditions may be necessary.
- Prognosis:
Life expectancy has improved over the years and many individuals lead healthy
and fulfilling lives with appropriate support.
