chapter 4- Genetic and Congenital Disorders

congenital disorders

birth defects; present at birth, the cause of genetic or nongenetic factors

genetic disorders

permanent change/mutation in the genome

genetic disorders

change in DNA base sequence as a result of deletion, invertion, duplication, translocation mutations(when one piece of chromosome splits off and combines to another)


location of a gene on a particular chromosome


alternative formes of the same gene; inherit 2 alleles for each gene (1 from mom, 1 from dad)


both alleles are identical


different alleles are present (carriers)


genetic composition of an individual


observed expression of the genotype (you can physically see it)


trait will be expressed in the heterozygote


trait will be expressed in the homozygote only (have to inherit 2 copies or wont see)

single gene disorders

follow Mendelian inheritance patters; can affect X/Y or autosomal chromosomes; examine patter of inheritance by looking at family genetic history; {a pedigree chart}

autosomal dominant disorders

single mutant allele transmitted from parent to offspring

reduced penetrance

person inherits the dominant mutant allele but doesnt express it

variable expressibility

disorders expressed differently by individuals with the mutant allele

Marfan syndrome

connective tissure disorder of skeleton (e.g. long, slinder fingers), eyes (dislocated lens, detached retina), & cardiovascular system (mitral valve prolapse, weakened aorta)


neurogenic tumors that arise from Schwann cells & other PNS elements

autosomal recessive disorders

seen only when both copies of the gene are affected {one copy makes you a carrier (Aa), two copies give you the disease (AA)}

X-linked disorders

affect males more than females; carrier mother has 50% chance of passing mutant X allele to offspring; sons will have disease & daughters will be carriers

fragile X Syndrome

fragile site on X chromosome; 1:1,250 males, 1:2,500 females

fragile X Syndrome

mental retardation & distinct physical phenotype (long face, large mandible, everted ears)

fragile X Syndrome

gene duplication affects proteins that aid communication between brain cells

multifactoral inherited disorders

multiple gene involvement; inheritance pattern unclear

congenital multifactoral disorders

cleft lip/palate, clubfoot, congenital heart disease

environmentally influenced multifactoral disorders

coronary artery disease, diabetes mellitus, hypertension, some cancers

mitochondrial gene disorders

rare, many affect neuromuscular system;
mitchondria contain small double-standed circular chromosome that codes for mitochondrial rRNA, tRNA, & proteins of oxidative phosphorylation

chromosomal disorders

usually result from abnormal chromosomal segregation during meiosis
lead to first-term abortions & identifiable sydromes

alterations in chomosome structure



loss of chromosomal region


simultaneous break in two different chromosomes with exchange of pieces


two breaks occur in a single chromosome & pieces are inverted when rejoined

alteration in chromosome number

aneuploidy {wrong chromosome #} due to nondisjunction errors during meiosis


more than two chromosomes of a particular type
ie. trisomy 21


only one member of a chromosome pair is present
ie. Turner syndrome

environmentally influenced disorders-
period of vulnerability

during first two weeks environmental influences can interfere with implantation lead to abortion
during organogenesis (day 15-60) differentiation/development of organs can be compromised

environmentally influenced disorders-
teratogenic agents

environmental agent tht produces abnormalities in embryo/fetus

environmentally influenced disorders-
teratogenic agents

chemicals & drugs
infectious agents


heavy doses of ionizing radiation (above diagnositc levels)

chemicals & drugs

cross placenta and have cytotoxic/antimetabolic effects

infectious agents

TORCH (toxoplasmosis, other, rubella, cytomegalovirus, herpes)

prenatal diagnosis

{for people who may be thinking about abortion}


determine gestational age, fetus number, position, amniotic fluid amount

maternal serum makers

16-18 weeks gestation

invasive testing

{increase probability of spontaneous abortion}

invasive testing-

15-18 week; amniotic fluid withdrawn & tested

invasive testing-
chorionic villus sampling

10-12 week; analyze fetal chromosomes

invasive testing-
percutaneous umbilical blood sampling

19-21 weeks; look for hemoglobin/clotting pathologies