11. (Non) Surviving Errors Flashcards
Damaged, broken, missing or extra (parts of) chromosomes
Translocation (13, 14, 15, 21, 22)
Fragile sites in chromosome, fragile X
Mosaicism
Few survive to full term
Produce variety of serious clinical conditions
Nondisjunction at first mitotic division
Disomic of nullisomic games (n+1 or n-1)
Disomic gametes give rise to trisomic embryos
Nullisomic gametes are nonviable (except X/Y chromosome)
Nondisjunction at second mitotic division
disomic, nullisomic, 2 euploid gametes (n+1, n-1, n, n)
If oocyte: hope that different oocyte becomes polar body → only 2 euploid gamets
Earlier defect → higher chance of defect
Leakage and amniotic fluid
Fetal (blood) cells escape placental barrier
Immune response to fetal cells: isoimmunization (leads to hemolysis of fetal blood and hence yellowness of skin)
Rhesus antigen (Rh- mom vs Rh+ fetus)
ABO blood groups
Mom makes IgM/IgG against A or B
IgM cannot pass through placenta, but IgG can (smaller)
ABO hemolytic disease of newborn (of red blood cells)
Direct: no increase in potency to attack later; effect is immediate
Amniotic fluid
Too little: fetus does not produce urine
Too much: fetus is not drinking (e.g., bowel obstruction)
Absorbed through skin and tissue (until keratinization of skin), drinking and breathing
Growth restrictions
Disruptions: (false) knots in in umbilical cord (hypoxia) and amniotic banding
Deformation: mechanical forces, clubfeet
Morphogens flukes
All morphogens that determine axis formation, outgrowth of tissue ro apoptosis should be present in an exquisite balance
SHH mutations affect midline
SHH and Gli3 mutations result in polydactyly
Hox gene mutations result in syndactyly
Absence of FGF8 could cause split foot anomaly
Spontaneous mutations
Changes in sequence of allele
Result of random errors in DNA replication
Errors detected and repaired by enzymes in nucleus
Undetected and unrepaired errors have potential to change phenotype
Where did mutation take place?
