In Class Notes 9/5: X-Linked Disorders and Genetic Vulnerability
Males are genetically more vulnerable to genetic disorders than females due to the presence of X-linked disorders, which are carried on the X chromosome.
For males, they only have one X chromosome (XY), so if they inherit an X with a genetic disorder, they are more likely to express the disorder.
For females, they have two X chromosomes (XX), so even if one X has a genetic disorder, the other X can compensate for it, making it less likely for the disorder to be expressed.
Hemophilia: a bleeding disorder where the blood doesn't clot properly
Color Blindness: a condition where a person has difficulty perceiving certain colors
Duchenne's Muscular Dystrophy: a genetic disorder that causes muscle weakness and degeneration
Learning Disabilities: such as dyslexia
Vision Disorders: such as the one that causes blindness by the age of 25
Ratio | |
Conception | 120 male fetuses : 100 female fetuses |
Birth | 104 males : 100 females |
Age 5 | 100 males : 100 females |
The ratio changes due to the presence of genetic disorders that may cause miscarriage or stillbirth.
Just because a gene is present, it doesn't necessarily mean it will be expressed. This can be due to various reasons, such as:
Blocking genes: one gene may block the expression of another gene
Polygenic traits: multiple genes are involved in the expression of a single trait
Regulator genes: genes that control the interactions of other genes and direct genetic expression
Regulator genes play a crucial role in epigenetics, controlling the interactions of other genes and directing genetic expression. Research in this area focuses on understanding how genes are turned on and off, and how to potentially prevent genetic disorders from being expressed.## Dominant and Recessive Genes 🧬
In the study of genetics, particularly in cancer research, understanding dominant and recessive genes is crucial.
What are dominant and recessive genes?
A dominant gene is a gene that will always be expressed if an individual has one copy of the gene. A recessive gene is a gene that will only be expressed if an individual has two copies of the gene.
Let's take eye color as an example. Brown eyes (B) are a dominant gene, and blue eyes (b) are a recessive gene.
BB or Bb: brown eyes (because the dominant gene B is present)
bb: blue eyes (because there are two copies of the recessive gene b)
A carrier is an individual who has a recessive gene that is not visible in their phenotype (physical appearance) but can still pass it on to their offspring.
A Punnett square is a tool used to predict the probability of certain traits being passed down to offspring.
B | b | |
B | BB | Bb |
b | bB | bb |
Two parents with brown eyes (Bb) can have a child with blue eyes (bb) if they both pass on their recessive gene.
An individual with brown eyes (Bb) can be a carrier of the recessive gene for blue eyes.
Definition: Identical twins are formed from a single fertilized egg that splits and develops into two separate embryos.
Characteristics:
Always the same sex
Same genotype (DNA)
May have slight differences in phenotype due to environmental influences
Definition: Fraternal twins are formed from two separate eggs that are fertilized by two separate sperm.
Characteristics:
Can be same or opposite sex
Genetically similar to any other siblings
More common than identical twins
Occurrence varies by ethnicity and age## Multiple Births and Prenatal Development 🤰
Identical twins (monozygotic): form from a single fertilized egg (zygote) that splits and develops into two separate embryos
Fraternal twins (dizygotic): form from two separate eggs, each fertilized by a different sperm
Ethnicity: some ethnic groups have a higher incidence of multiple births
Age: older women are more likely to have multiple births
Fertility treatments: certain fertility drugs can increase the chances of multiple births
Period | Duration | Description |
Germinal period | 1-14 days | rapid cell division and growth, development of placenta and umbilical cord |
Embryonic period | 3-8 weeks | cells start to differentiate, beginning of brain development |
Fetal period | 9 weeks - birth | rapid growth and development of fetus |
Miscarriage: can occur due to genetic problems, chromosomal abnormalities, or errors during rapid cell division
67% of zygotes do not survive the germinal period
20% of embryos are miscarried or spontaneously aborted during the embryonic period
5% of fetuses are miscarried before viability (22 weeks)
Rapid cell division and growth
Development of placenta and umbilical cord
Monozygotic twins form during this period
Cells start to differentiate
Beginning of brain development with the primitive streak
Folic acid is essential for neural tube formation and brain and spinal cord development
Prevents neural tube defects
Essential for brain and spinal cord development
Campaigns to increase folic acid in food supply to reduce neural tube defects## Folic Acid and Prenatal Development 🧬
Folic acid is a crucial vitamin that plays a significant role in preventing neural tube defects during pregnancy. Neural tube defects occur when the brain and spinal cord do not form properly. To combat this, folic acid is often added to foods such as orange juice, breakfast cereal, and bread, which is indicated by the label "enriched with folic acid."
During this stage, the head starts to take shape, and the eyes, ears, nose, and mouth begin to form. The heart starts to pulsate, and extremities such as arms and legs begin to develop. Initially, fingers and toes are webbed, but this disappears towards the end of this stage.
Here are some key features of embryonic development:
The head starts to take shape
Eyes, ears, nose, and mouth begin to form
Heart starts to pulsate
Extremities (arms and legs) begin to develop
Fingers and toes are initially webbed
Prenatal tests are crucial during pregnancy to identify and prevent potential issues. Some common tests include:
Test | Purpose |
Vaccination check | Ensure immunity levels are adequate |
Blood and urine tests | Detect infections and other issues |
Ultrasound | Check for structural problems, e.g., heart defects |
Amniocentesis | Screen for genetic problems, e.g., Down syndrome |
Glucose testing | Detect gestational diabetes |
Glucose testing is used to detect gestational diabetes, a condition where the body struggles to handle sugar levels during pregnancy. The test involves drinking a sugary drink and then testing blood sugar levels. If diagnosed, gestational diabetes can be managed through diet control and, in some cases, insulin treatment.
During this period, the brain continues to grow and develop, with significant growth between 4-6 months. The saccharin organs form, and differences in brain organization occur due to hormone levels. The eyes and lungs are the last organs to mature.
Here are some key features of fetal development:
Brain growth and development
Saccharin organs form
Differences in brain organization occur due to hormone levels
Eyes and lungs are the last organs to mature## Fetal Development during Pregnancy 🤰
The growth range of a fetus during pregnancy is influenced by:
Genetics: The parents' size and genetic makeup can affect the baby's size.
Nutrition: The mother's nutrition during pregnancy affects the baby's growth.
Environmental factors: External factors, such as exposure to teratogens, can impact fetal development.
At 25 days, the neural tube forms and eventually develops into the brain and spinal cord.
By 9 months, the brain has a more developed structure, but it's still not fully developed until around 3 years after birth.
Month | Description |
1 | Looks like a "little dot" |
2 | Big headed alien |
4-9 | Gradually develops into a more familiar shape |
Head down positioning: Crucial for a safe delivery, as the head is larger compared to the rest of the body.
Reason for head-first delivery: Prevents the baby from getting stuck in the pelvic cavity.
Manual turning: A procedure performed by doctors to turn the baby's head down if necessary.
Age of viability: The age at which a premature infant might survive with adequate medical care.
Chances of survival: Decrease with earlier birth and are influenced by lung development.
Too many chromosomes: Having an extra chromosome on a certain pair (e.g., Trisomy 21, which causes Down syndrome).
Too few chromosomes: Missing a chromosome on a certain pair.
Damaged chromosomes: Chromosomes damaged during cell division.
Older parents: More likely to have a child with chromosomal abnormalities due to issues with DNA in sperm or egg cells.## Genetic Disorders 🧬
Genetic disorders can be categorized into two types: single gene disorders and polygenic disorders. Single gene disorders are caused by a mutation in a single gene, while polygenic disorders involve multiple genes.
Genotype vs. Phenotype
Examples of Genetic Disorders
Huntington's disease
Cystic fibrosis
Thalassemia
Sickle cell disease
Fragile X syndrome
These disorders are caused by dominant or recessive genes. Recessive disorders are more common and require an individual to inherit the gene from both parents.
Spontaneous Mutations
Spontaneous mutations occur when a genetic error occurs during DNA replication, often due to exposure to teratogens such as radiation or pollution. The frequency of chromosomal issues increases with advanced maternal age (over 35) or paternal age (over 40).
Recessive Disorders and Evolution
Researchers believe that some recessive disorders may have originated because being a carrier of the disorder provided protection against another disorder. For example, sickle cell trait may have originated in regions with high malaria prevalence, as carriers of the trait have an increased immunity to malaria.
Definitions
Term | Definition |
Preterm | Born before 35 weeks |
Premature | Born before 35 weeks |
Small for Gestational Age (SGA) | Born at or after 36 weeks, but weighing less than expected |
Preterm babies are often small due to premature birth, while SGA babies may experience prenatal development issues due to teratogens or maternal health factors.
Risk Factors for Low Birth Weight
Chronic maternal health issues
Experimental illnesses during pregnancy
Maternal use of tobacco products or certain prescription medications
Maternal illegal drug use
Low socioeconomic status
Lack of prenatal care
Chronic stress
Consequences of Low Birth Weight
Delayed developmental milestones (e.g. sitting, crawling, walking, reading)
Increased crying due to immature nervous system
Attention issues
Behavioral issues
Language delays
Learning disabilities
Neurological delays
Smaller brain volume
These consequences can persist throughout childhood and into adulthood, highlighting the importance of addressing low birth weight.
Males are genetically more vulnerable to genetic disorders than females due to the presence of X-linked disorders, which are carried on the X chromosome.
For males, they only have one X chromosome (XY), so if they inherit an X with a genetic disorder, they are more likely to express the disorder.
For females, they have two X chromosomes (XX), so even if one X has a genetic disorder, the other X can compensate for it, making it less likely for the disorder to be expressed.
Hemophilia: a bleeding disorder where the blood doesn't clot properly
Color Blindness: a condition where a person has difficulty perceiving certain colors
Duchenne's Muscular Dystrophy: a genetic disorder that causes muscle weakness and degeneration
Learning Disabilities: such as dyslexia
Vision Disorders: such as the one that causes blindness by the age of 25
Ratio | |
Conception | 120 male fetuses : 100 female fetuses |
Birth | 104 males : 100 females |
Age 5 | 100 males : 100 females |
The ratio changes due to the presence of genetic disorders that may cause miscarriage or stillbirth.
Just because a gene is present, it doesn't necessarily mean it will be expressed. This can be due to various reasons, such as:
Blocking genes: one gene may block the expression of another gene
Polygenic traits: multiple genes are involved in the expression of a single trait
Regulator genes: genes that control the interactions of other genes and direct genetic expression
Regulator genes play a crucial role in epigenetics, controlling the interactions of other genes and directing genetic expression. Research in this area focuses on understanding how genes are turned on and off, and how to potentially prevent genetic disorders from being expressed.## Dominant and Recessive Genes 🧬
In the study of genetics, particularly in cancer research, understanding dominant and recessive genes is crucial.
What are dominant and recessive genes?
A dominant gene is a gene that will always be expressed if an individual has one copy of the gene. A recessive gene is a gene that will only be expressed if an individual has two copies of the gene.
Let's take eye color as an example. Brown eyes (B) are a dominant gene, and blue eyes (b) are a recessive gene.
BB or Bb: brown eyes (because the dominant gene B is present)
bb: blue eyes (because there are two copies of the recessive gene b)
A carrier is an individual who has a recessive gene that is not visible in their phenotype (physical appearance) but can still pass it on to their offspring.
A Punnett square is a tool used to predict the probability of certain traits being passed down to offspring.
B | b | |
B | BB | Bb |
b | bB | bb |
Two parents with brown eyes (Bb) can have a child with blue eyes (bb) if they both pass on their recessive gene.
An individual with brown eyes (Bb) can be a carrier of the recessive gene for blue eyes.
Definition: Identical twins are formed from a single fertilized egg that splits and develops into two separate embryos.
Characteristics:
Always the same sex
Same genotype (DNA)
May have slight differences in phenotype due to environmental influences
Definition: Fraternal twins are formed from two separate eggs that are fertilized by two separate sperm.
Characteristics:
Can be same or opposite sex
Genetically similar to any other siblings
More common than identical twins
Occurrence varies by ethnicity and age## Multiple Births and Prenatal Development 🤰
Identical twins (monozygotic): form from a single fertilized egg (zygote) that splits and develops into two separate embryos
Fraternal twins (dizygotic): form from two separate eggs, each fertilized by a different sperm
Ethnicity: some ethnic groups have a higher incidence of multiple births
Age: older women are more likely to have multiple births
Fertility treatments: certain fertility drugs can increase the chances of multiple births
Period | Duration | Description |
Germinal period | 1-14 days | rapid cell division and growth, development of placenta and umbilical cord |
Embryonic period | 3-8 weeks | cells start to differentiate, beginning of brain development |
Fetal period | 9 weeks - birth | rapid growth and development of fetus |
Miscarriage: can occur due to genetic problems, chromosomal abnormalities, or errors during rapid cell division
67% of zygotes do not survive the germinal period
20% of embryos are miscarried or spontaneously aborted during the embryonic period
5% of fetuses are miscarried before viability (22 weeks)
Rapid cell division and growth
Development of placenta and umbilical cord
Monozygotic twins form during this period
Cells start to differentiate
Beginning of brain development with the primitive streak
Folic acid is essential for neural tube formation and brain and spinal cord development
Prevents neural tube defects
Essential for brain and spinal cord development
Campaigns to increase folic acid in food supply to reduce neural tube defects## Folic Acid and Prenatal Development 🧬
Folic acid is a crucial vitamin that plays a significant role in preventing neural tube defects during pregnancy. Neural tube defects occur when the brain and spinal cord do not form properly. To combat this, folic acid is often added to foods such as orange juice, breakfast cereal, and bread, which is indicated by the label "enriched with folic acid."
During this stage, the head starts to take shape, and the eyes, ears, nose, and mouth begin to form. The heart starts to pulsate, and extremities such as arms and legs begin to develop. Initially, fingers and toes are webbed, but this disappears towards the end of this stage.
Here are some key features of embryonic development:
The head starts to take shape
Eyes, ears, nose, and mouth begin to form
Heart starts to pulsate
Extremities (arms and legs) begin to develop
Fingers and toes are initially webbed
Prenatal tests are crucial during pregnancy to identify and prevent potential issues. Some common tests include:
Test | Purpose |
Vaccination check | Ensure immunity levels are adequate |
Blood and urine tests | Detect infections and other issues |
Ultrasound | Check for structural problems, e.g., heart defects |
Amniocentesis | Screen for genetic problems, e.g., Down syndrome |
Glucose testing | Detect gestational diabetes |
Glucose testing is used to detect gestational diabetes, a condition where the body struggles to handle sugar levels during pregnancy. The test involves drinking a sugary drink and then testing blood sugar levels. If diagnosed, gestational diabetes can be managed through diet control and, in some cases, insulin treatment.
During this period, the brain continues to grow and develop, with significant growth between 4-6 months. The saccharin organs form, and differences in brain organization occur due to hormone levels. The eyes and lungs are the last organs to mature.
Here are some key features of fetal development:
Brain growth and development
Saccharin organs form
Differences in brain organization occur due to hormone levels
Eyes and lungs are the last organs to mature## Fetal Development during Pregnancy 🤰
The growth range of a fetus during pregnancy is influenced by:
Genetics: The parents' size and genetic makeup can affect the baby's size.
Nutrition: The mother's nutrition during pregnancy affects the baby's growth.
Environmental factors: External factors, such as exposure to teratogens, can impact fetal development.
At 25 days, the neural tube forms and eventually develops into the brain and spinal cord.
By 9 months, the brain has a more developed structure, but it's still not fully developed until around 3 years after birth.
Month | Description |
1 | Looks like a "little dot" |
2 | Big headed alien |
4-9 | Gradually develops into a more familiar shape |
Head down positioning: Crucial for a safe delivery, as the head is larger compared to the rest of the body.
Reason for head-first delivery: Prevents the baby from getting stuck in the pelvic cavity.
Manual turning: A procedure performed by doctors to turn the baby's head down if necessary.
Age of viability: The age at which a premature infant might survive with adequate medical care.
Chances of survival: Decrease with earlier birth and are influenced by lung development.
Too many chromosomes: Having an extra chromosome on a certain pair (e.g., Trisomy 21, which causes Down syndrome).
Too few chromosomes: Missing a chromosome on a certain pair.
Damaged chromosomes: Chromosomes damaged during cell division.
Older parents: More likely to have a child with chromosomal abnormalities due to issues with DNA in sperm or egg cells.## Genetic Disorders 🧬
Genetic disorders can be categorized into two types: single gene disorders and polygenic disorders. Single gene disorders are caused by a mutation in a single gene, while polygenic disorders involve multiple genes.
Genotype vs. Phenotype
Examples of Genetic Disorders
Huntington's disease
Cystic fibrosis
Thalassemia
Sickle cell disease
Fragile X syndrome
These disorders are caused by dominant or recessive genes. Recessive disorders are more common and require an individual to inherit the gene from both parents.
Spontaneous Mutations
Spontaneous mutations occur when a genetic error occurs during DNA replication, often due to exposure to teratogens such as radiation or pollution. The frequency of chromosomal issues increases with advanced maternal age (over 35) or paternal age (over 40).
Recessive Disorders and Evolution
Researchers believe that some recessive disorders may have originated because being a carrier of the disorder provided protection against another disorder. For example, sickle cell trait may have originated in regions with high malaria prevalence, as carriers of the trait have an increased immunity to malaria.
Definitions
Term | Definition |
Preterm | Born before 35 weeks |
Premature | Born before 35 weeks |
Small for Gestational Age (SGA) | Born at or after 36 weeks, but weighing less than expected |
Preterm babies are often small due to premature birth, while SGA babies may experience prenatal development issues due to teratogens or maternal health factors.
Risk Factors for Low Birth Weight
Chronic maternal health issues
Experimental illnesses during pregnancy
Maternal use of tobacco products or certain prescription medications
Maternal illegal drug use
Low socioeconomic status
Lack of prenatal care
Chronic stress
Consequences of Low Birth Weight
Delayed developmental milestones (e.g. sitting, crawling, walking, reading)
Increased crying due to immature nervous system
Attention issues
Behavioral issues
Language delays
Learning disabilities
Neurological delays
Smaller brain volume
These consequences can persist throughout childhood and into adulthood, highlighting the importance of addressing low birth weight.