Heredity
genetic disorders/ inherited disorders are disorders that can be passed from one generation to the next
- disorder in the gene or chromosome structure
- alterations of a whole chromosome, a part of a chromosome or even a single gene manifest as a genetic disorder
Chromosomes
44 autosomes (22 pairs) 2 sex chromosomes (1 pair)
Phenotype
expression of the gene (appearance of the gene)
Genotype
composition of the gene
Genome
Complete set of genes
Homozygous
two like genes for a trait
Heterozygous
Unlike genes for a trait
Dominant
dominant in their action over others
Recessive
a gene that is not dominant
Autosomal dominance
- person with dominant gene for a disease is usually heterozygous
- huntington’s chorea, OI, marfan syndrome
- one dominant gene and one healthy gene
Two dominant genes mean….
never good
-baby will not survive
Autosomal recessive
- most genetic disorders are inherited as recessive traits
- does not occur unless 2 genes for the disease are present
- many unborn errors (cystic fibrosis, tay sachs, galactosemia, pku)
X-linked dominant (sex linked dominant)
- some genes for disorders are located on and transmitted only be female sex chromosome (X)
- no carriers in X linked dom.
X-linked recessive
- majority of x-linked disorders are recessive
- female- normal gene also present blocks expression of the disease
- Only male children will have the disease
- muscular dystrophy, hemophilia
- daughters are the carriers but not affected
Multifactorial (polygenic)
- congenital disorders present at birth, heart disease, HTN, DM, Pyloric stenosis, cleft lip/palate, NTD, mental illness
- Environmental influences determine if the disorder is expressed
Non-dysjunction
- meiosis
- -cell division, number of chromosomes in cell reduced to 1/2 for repro., non-dysjunction is when the division is uneven
- presence of 45 is incompatible with life
- can also occur with sex chromosomes
Deletion abnormalities
-a part of the chromosome breaks during cell division causing a normal number of chromosomes plus or minus an extra portion of a chromosome
Translocation abnormalities
- 2 non-homologous chromosomes that exchange material
- child gains an additional chromosome through another route
- have the correct numbers of chromosomes
- balanced translocation
- unbalanced translocation
Duplication abnormalities
part of chromosome is included twice (been repeated)
Inversion abnormalities
linear stretch of DNA is reversed within the chromosome
Mosaicism
- non-dysjunction disorder-did not divide evenly
- occurring after fertilization of the ovum as the structure begins mitotic division
Karotyping
- visual presentation of a person’s chromosome pattern
- blood sample or scraping of cells from buccal membrane
Barr body determination
- determine sex of child
- scrape cells from buccal cavity, stain, and magnify
Amniocentesis
- watch fetal heart rate after
- time frame: 14-16 weeks gestation
- locate pocket of amniotic fluid via ultrasound
- risks: infection, spotting, leakage, cramping, fetal loss
