Chromosomal disorders Flashcards
what happenes in Meiotic Nondisjunction?
In meiotic nondisjunction two chromosome homologs migrate to the same daughter cell instead of disjoining and migrating to different daughter cells
Fertilization with normal gamete produces Monosomic or Trisomic offspring
Many trisomies are ——–?
Trisomy —– is the most common surviving trisomy Trisomies of the ____ and ____ chromosomes are much less common at birth
Many trisomies are not compatible with survival Trisomy 21 is the most common surviving trisomy Trisomies of the 13th and 18th chromosomes are much less common at birth
Down Syndrome problems
Mental retardation, GI tract obstructions, Congenital heart defects, Respiratory infections and Leukemia
Down Syndrome is?
Trisomy 21 Most common autosomal aneuploidy among live births Extra chromosome 21 contributed by the mother in 95% of cases
Mosaicism: 1-3% of DS cases Usually milder phenotype
Down Syndrome features
- Upslanting palpebral fissures (Almond-shaped opening between the upper and lower eyelids)
- Epicanthic (fold Redundant skin of the inner eyelid)
- Low nasal bridge
- Brushfield spot: Light smudgy opacity of the pupil
- Simian crease: A single crease extends transversely across the palm
Down Syndrome Mosaicism
Condition in which an individual organism has: Two or more genetically distinct cell lines
Derived from a single zygote Their difference due to: Mutation or Nondisjunction
Trisomy 18 characteristics
Edwards syndrome Prevalence: 1/6000 at birth Male/female = ¼
Intrauterine growth retardation
Microcephaly
- Small mouth, palpebral fissures
- Cardiac defects
- Overlapping fingers
- Omphalocele Congenital herniation of viscera into the base of the umbilical cord
- Still born/most die w/in 2 months <10% survive 1 year
Patau Syndrome (Trisomy 13) Newborn male with trisomy 13 has? He is? Survival beyond the ____ is rare
Newborn male with trisomy 13 has Cleft palate Atrial septal defect, Inguinal (groin) hernia, and Post axial polydactyly of the left hand
He is Deaf Legally blind
Survival beyond the 1st year is rare
Polydactyly
Affecting all extremities, strongly suggests trisomy 13 Extra toes on each foot
An extra finger on the hand of an infant with trisomy 13
Trisomy 13 cleft lip & Cyclopia with a proboscis
baby on the top with cleft lip associated with trisomy 13
baby on the bottom with trisomy 13 has Cyclopia (single eye) and Proboscis (the projecting tissue just above the eye)
Monosomy X Turner syndrome, karyotype? look for?
Caused by 45,X karyotype
Common at conception Rare among live birth ( Spontaneous abortion)
Mosaicism increase probability of survival to term
reduced Stature, and Swelling (edema) in the ankles and wrists
A female with Turner syndrome (45,X) Characteristics
Characteristically broad “webbed” neck
Reduced stature
Poorly developed sexual secondary characteristics Usually infertile because of gonadal dysgenesis
Rarely undergo menarche
Estrogen treatment Around 30-40% mosaic, mostly 45,X/46,XX TS females are sterile
Fetal hydrops
when fitus Soft tissues are markedly edematous Body cavities filled with effusions
feature of many chromosomal abnormalities including monosomy X
Turner Syndrome: cystic hygroma
Results from failure of lymphatics to form and drain properly
Cystic hygroma forms the “web neck” of TS women
Gray coloration from
prolonged intrauterine demise
A male with Klinefelter syndrome (47,XXY)
Increased stature, Gynecomastia (enlarged breast), Feminine body shape, Reduced IQ, Usually sterile
Testosterone therapy Mastectomy
Trisomy X (47,XXX Karyotype)
Occurs in 1 in 1000 females with benign consequences
Sometimes: Sterility Menstrual irregularity, Mild mental retardation
Mostly result from nondisjunction in the mother Incidence increases with the mother’s age
Females with more X chromosomes exist But more is not better Each additional X chromosome leads to more mental and physical abnormalities
hypertelorism
Abnormal distance between two paired organs. in Trisomy X look btw eye brows
47, XYY Male Karyotype: Jakob syndrome
These males tend to be taller
Have 10- to 15-point reduction in IQ ? (New studies say no or little difference) ?
Few physical problems
Notorious because 1/30 of prison population compared to1/1000 in the general male population (Studies refute association with violent crime)
Minor behavioral problems: Hyperactivity Attention deficit disorder Learning disabilities
XX Male & XY Female
Result from mutation in the SRY (sex-determining region on the Y) or Transfer of SRY from Y to X chromosome during crossing-over between the X & Y chromosomes in male meiosis
Albinism
Deficiency of the pigment melanin from Skin Hair Eye can be complete or partial
Albinism: Causes, types
Inability to produce or distribute melanin ➔ Albinism
Tyrosine metabolism defects lead to failure to convert it into melanin ➔albinism
Different forms of albinism and several modes of inheritance: Autosomal recessive, Autosomal dominant, X-linked inheritance
Complete albinism Affected people may have
Affected people may have White hair, skin, and iris
Vision defects, Photophobia, Sunburn easily Should never try to tan
Ocular albinism is
Albinism of the eyes only Skin color is normal
Eye color may be in the normal range Brown, blue, green BUT: No pigment in the retina
Chédiak-Higashi syndrome
Partial albinism
Autosomal recessive
Silver hair, ocular albinism –Immune system deficiency Infections of lungs, skin & mucosa —EBV affects these children leading to child lymphoma
Nystagmus (jerky eye movement) Muscle weakness Nervous system Tremors Seizures Ataxia/unsteady walking
