Genetics (CHP 5) Flashcards
Define basic terms used in genetics. Compare and contrast single-gene, chromosomal, and multifactorial disorders. Summarize causes and manifestations of autosomal recessive, autosomal dominate, X-linked inheritance disorders, and mitochondrial gene disorders. Differentiate how environmental influences (such as teratogens) can affect embryo and fetal development.
What is a mutation/mutagen?
A biochemical event, such as nucleotide change, deletion, or insertion that produces a new allele for a particular gene.
Define locus in genetics.
A specific location that one gene occupies.
What is an allele?
Two members of a gene pair, one inherited from the mother and the other from the father.
Differentiate between homozygous and heterozygous.
- Homozygous: members of gene pair are identical
- Heterozygous: two members are different.
Define expressivity in genetics.
How much a trait is expressed in a person.
What is penetrance?
The percentage of people with a gene who have the associated trait.
True or False: A 50% penetrance indicates that a person who inherits the defective gene has a 50% chance of expressing the disorder.
True.
Differentiate between dominant and recessive traits.
- Dominant: trait is phenotypically seen in the heterozygote
- Recessive: phenotypically seen only in the homozygote.
What is a carrier in genetics?
An individual who possesses one copy of a mutated gene associated with a disease but does not exhibit symptoms.
Define autosomal in genetics.
A specific gene that is not on a sex chromosome and is a numbered chromosome.
What are chromosomes?
Thread-like structures located inside the nucleus of a cell, composed of DNA and proteins, which carry genetic information.
What are gametes?
Reproductive cells of an animal or plant.
Define somatic cells.
Any cell of a living organism other than the reproductive cells.
What is mitosis?
A type of indirect cell division that occurs in somatic cells resulting in the formation of two daughter nuclei containing identical complements of chromosomes.
Define meiosis.
The division of a sex cell as it matures, so that each daughter nucleus receives one half of the number of chromosomes characteristic of the somatic cells.
What is a karyotype?
The total chromosomal characteristics of a cell, or the micrograph of chromosomes arranged in pairs in descending order of size.
What is a pedigree?
A systematic presentation of an individual’s ancestors used in human genetics to analyze inheritance.
Define genogram.
A visual diagram that depicts a person’s family relationships across multiple generations.
What are single-gene disorders?
Disorders caused by a defective or mutant allele at a single gene locus that follow Mendelian patterns of inheritance.
What is the etiology of autosomal dominant disorders?
A single mutant allele from an affected parent is transmitted to offspring regardless of sex.
What is reduced penetrance?
When an individual inherits a dominant mutant gene but fails to exhibit the phenotype.
Give an example of an autosomal dominant disorder.
Marfan Syndrome.
What is neurofibromatosis?
A disorder that causes tumors to develop from schwann cells due to a genetic defect in a tumor suppressor gene.
What are the characteristics of Type 1 Neurofibromatosis?
- Cutaneous and subcutaneous neurofibromas
- Pigmented nodules of iris (Lisch nodules)
- Café au lait spots.
What are autosomal recessive disorders?
Disorders where both members of the gene pair are affected, and parents could be unaffected but carriers.
What is phenylketonuria (PKU)?
A disorder caused by a deficiency of the liver enzyme phenylalanine hydroxylase.
What is Tay-Sachs disease?
A lysosomal storage disease caused by the accumulation of GM2 ganglioside in neurons.
What are X-linked disorders?
- X-linked recessive disorders: almost always affect males
- X-linked dominant disorders: affected females transmit the disorder to 50% of offspring.
What is Fragile X syndrome?
A genetic disorder that causes intellectual disability, primarily affecting males.
What are inherited multifactorial disorders?
Disorders caused by multiple genes along with environmental factors that do not follow clear-cut patterns of inheritance.
What is a teratogen?
An environmental factor that can cause malformation of an embryo.
What is aneuploidy?
Having an abnormal number of chromosomes.
Define non-disjunction.
Failure of the chromosomes to separate during oogenesis or spermatogenesis.
What is monosomy?
Presence of only one member of a chromosome pair.
What is polysomy?
Presence of more than 2 chromosomes to a set.
Give an example of a trisomy disorder.
Down syndrome (trisomy 21).
What is Turner syndrome?
A condition in females characterized by short stature and loss of oocytes, leading to no menstruation.
What is Klinefelter syndrome?
A condition in males caused by testicular dysgenesis and the presence of one or more extra X chromosomes.
What is a mitochondrial gene disorder?
Disorders caused by mutations in mitochondrial DNA that affect tissues dependent on oxidative phosphorylation.
What is organogenesis?
The process of differentiation and development of organs occurring from day 15 to day 60 after conception.
What are common disorders of the neuromuscular system?
Encephalopathies, myopathies, retinal degeneration, loss of extraocular muscle function, deafness
These disorders can significantly affect motor and sensory functions.
What are teratogens?
Environmental influences that can adversely affect embryo and fetal development
Teratogens can lead to various developmental disorders or malformations.
What is organogenesis?
The process of differentiation and development of the organs
This process occurs from day 15 to day 60 after conception.
What is the period of vulnerability in embryonic development?
Each organ has a critical period where it is highly susceptible to damage
This means that certain stages of development are more sensitive to environmental influences.
What may influences during the first 2 weeks of pregnancy result in?
Interference with implantation, resulting in abortion or early resorption
This highlights the importance of early prenatal care.
How can teratogenic agents affect an embryo?
Through direct exposure of the mother and fetus, exposure of soon-to-be pregnant females, or mutagenic effects before pregnancy
These pathways can lead to permanent reproductive cell damage.
What are some disorders caused by radiation exposure during pregnancy?
Microcephaly, skeletal malformations, mental retardation
Radiation can cause inheritable changes in genetic materials.
What factors affect placental drug transfer?
- Rate at which the drug crosses
- Duration of exposure
- Stage of placental/fetal development
- Molecular weight
These factors influence the potential risks to the developing embryo.
What does the FDA classification system (ABCDX) signify?
A = least dangerous, X = contraindicated
This system helps assess the risk of drug use during pregnancy.
What are the effects of thalidomide on fetal development?
Full range malformations including phocomelia
Phocomelia refers to short, flipper-like appendages on all four limbs.
What is Fetal Alcohol Syndrome (FAS)?
A condition caused by alcohol exposure during pregnancy leading to growth retardation and CNS abnormalities
FAS is characterized by distinct facial features and varying severity based on exposure.
What are the characteristic facial features of Fetal Alcohol Syndrome?
- Small palpebral fissures
- Thin vermillion border
- Elongated, flattened midface and philtrum
These features become more subtle in adulthood.
What does the acronym TORCH represent in terms of infections?
- Toxoplasmosis
- Other (e.g., Listeriosis, Leptospirosis)
- Rubella
- Cytomegalovirus
- Herpes
These infections can cross the placenta and affect fetal development.
What are potential disorders caused by maternal infections during pregnancy?
Growth retardation, brain abnormalities, eye and ear abnormalities, hematopoietic system issues
These can lead to severe developmental complications.
What is the etiology of folic acid deficiency during pregnancy?
Not enough folic acid intake
This deficiency can lead to neural tube defects (NTDs) in the developing fetus.
What is the recommended daily intake of folic acid for pregnant women?
0.4 mg daily
This is crucial for the prevention of neural tube defects.
Fill in the blank: The effects of folic acid deficiency in embryonic development lead to _______.
neural tube defects
This underscores the importance of adequate folic acid during pregnancy.
