6. Hereditary and Environmental Influences on Development (Genetics) Flashcards
Hereditary Influences
* Directions for cellular function are provided by the genes located on __ chromosomes in every somatic cell
* Too much or too little genetic material results in abnormal structure or function
* Ranges from annoying to life-threatening conditions
46
DNA
* Basic building blocks of genes and chromosomes
* Consists of 3 units:
> ___, ___, 1 of 4 ___
* Resembles a spiral ladder
* Sequencing of base pairs
* If the sequence is incorrect or there are missing or added bases, a defect in body structure or function may occur
sugar, phosphate group, 1 of 4 nitrogen bases
___
* A segment of DNA that directs that production of a specific body structure or function
* Approximately 25,000-35,000 in each cell
Genes
___
> A gene that alters or harms functions
___
> A complete set of DNA that determines the traits of a person
___
> Genes that encode for the same trait
Mutations
Genome
Alleles
Chromosomes
> Genes are organized into 46 paired chromosomes
> 22 pairs are ___ (not sex)
> 23rd pair contains the sex chromosomes (XX females, XY males)
> Mature gametes (reproductive cells) are ___
→ Have half the chromosomes (23) of other body cells
> Allows for variation of genetic traits
autosomes
haploid
Genetic Analysis
?
Photographing or using computer imaging allows chromosomes to be displayed from largest to smallest pairs
Karyotype
Chromosome analysis
* Cells for chromosome analysis must have a nucleus and must be living
* Can be studied using any type of cells - e.g. blood, bone marrow, fetal cells
Transmission of Traits by Single Genes
Alleles
> ___ (identical) or ___ (different)
Dominance
> ___ (observable characteristics)
* e.g. blood types A and B dominant/O recessive
Chromosome location
Homozygous; heterozygous
Phenotype
Patterns of Single-Gene Inheritance
Inheritance pattern - ___ or ___
Autosomal dominant trait
> Produced by a dominant gene on a non-sex chromosome
genogram; pedigree
Autosomal ___
> A person receives two copies of an inferior gene carried on an autosome
X-linked
recessive
Single-Gene Abnormalities
* A person affected with an autosomal dominant disorder has a __% chance of transmitting the disorder to each child
* Two healthy parents who carry the same abnormal autosomal recessive gene have a __% chance of having a child affected with the disorder
50%
25%
Single-Gene Abnormalities
* Parental ___ (blood relationship) increases the risk of having a child with an autosomal recessive disorder
* One copy of an abnormal X-linked recessive gene is enough to produce the disorder in a male
* Abnormal genes can arise as new mutations
consanguinity
Chromosome Abnormalities
Structural
> Part of a chromosome missing or added
> Rearranged DNA within chromosomes
> One or part of a chromosome attached to another - ___
__ __ syndrome
> A site on the X chromosome is more fragile than normal
> More severe in males (only one X) and most common cause of intellectual disability
> Inherited in an X-linked ___ pattern
translocation
Fragile X
dominant
Chromosome Abnormalities
Numerical
> Entire single chromosome added (___)
> Entire single chromosome missing (___)
> One or more added sets of chromosomes (___)
trisomy
monosomy
polyploidy
Multifactorial Disorders - Characteristics of
> Interaction of genetic and environmental factors
> Present and detectable at birth
> Isolated defect
> May cause a secondary defect
> Examples include:
→ Heart defects
→ Neural tube defects
→ Cleft lip or palate
→ Pyloric stenosis
Multifactorial Disorders - Risk for occurrence
> Number of affected close relatives
> Severity of the disorder
> Sex of the affected person
> Geographic location
> Seasonal variations
Environmental Influences
___ (harmful)
> Agents in the fetal environment that either cause a birth defect or increase the likelihood that a birth defect will occur
Types of
> Maternal infectious agents (viruses/bacteria) that cross placenta
> Drugs and other substances (chemicals)
> Pollutants, chemicals, and other substances mother is exposed to
> Ionizing radiation
> Maternal hyperthermia
> Effects of maternal disorders such as diabetes or phenylalanine hydroxylase deficiency (PKU)
Teratogens
Mechanical Disruption to Fetal Development
___
> Results from tears in the amnion - inner sac of the fetal membranes
> Can result in fetal deformations or intrauterine limb amputation
Fibrous amniotic bonds
___
> An abnormally small volume of amniotic fluid which reduces the cushion surrounding the fetus
> May result in deformity such as clubfoot
Oligohydramnios
Genetic Counseling
* Provides services to help people understand disorders and levels of risk
> Availability
* Incorporated into nursing curriculum
> Focus on the family
* Multidisciplinary approach
> Healthcare legislation
* Genetic Information & Nondiscrimination Act (GINA) - protects patients against genetic discrimination
> Process of genetic counseling
* Preconception screening
* Prenatal diagnosis for fetal abnormalities
* Postnatal diagnosis for an infant with a birth defect
> Supplemental services
* Support groups
* Grief counseling
> Nurse as part of the genetic counseling team
* Counseling
* Guidance through prenatal diagnosis
* Support
* Coordinating services
* Help in establishing connection with support groups
> Nurses in general practice
* Women’s Health nurses
* Antepartum nurses
- Identifying families for referral
- Helping the woman decide about genetic counseling
- Teaching about lifestyle
- Providing emotional support
- Helping the woman and family deal with abnormal results
* Intrapartum and neonatal nurses
* Pediatric nurses
Reasons for Referral to a Genetic Counselor
* Pregnant woman who will be ___ years or older when the infant is born
* Men who father children after ___ years of age
* Members of groups with increased incidence of a specific disorder
* Carriers of autosomal ___ disorder
* Women who are carriers of X-linked disorders
* Couples related by blood
35
40
recessive
Reasons for Referral to a Genetic Counselor cont’d
* Family history of birth defects
* Family history of unexplained stillbirth
* Women who experience multiple spontaneous abortions
* Pregnant women exposed to teratogens before or during pregnancy
* Pregnant women with abnormal prenatal screening results
