GENETIC DISORDERS SBI3U

HEREDITARY DISORDERS (nature) - genetic abnormalities caused by recombination aneuploidy, sex-linked, nondisjunction CONGENITAL DEFECTS (nurture) - abnormalities caused by embryonic and/or developmental anomalies cleft lip/palate, conjoined, fetal alcohol syndrome

ALBINISM Autosomal recessive Lack of melanin pigment Panamanian tribe “Moon children”

CHROMOSOME DELETION Chromosome 2 - short arm Physical challenges Limited mental development Decreased vision acuity Most chromosome deletions result in spontaneously aborted pregnancies

SEX CHROMOSOME ABNORMALITIES XYGenotypic male XXGenotypic female XOTurner’s Syndrome - nondisjunction XXYKlinefelter’s Syndrome - nondisjunction XYY “Super” male - nondisjunction

TURNER’S SYNDROME XO Two sets of autosomes but only one sex chromosome 97% spontaneous abortions Female - short and sexually undeveloped (infertile) Webbing of the neck Wide chest with broadly spaced nipples Narrowing of the aorta

KLINEFELTER’S SYNDROME XXY Phenotype is not strikingly different form XY and not apparent until after puberty Extremities are longer 50% develop breasts Body hair is sparse (female pattern) Somewhat mentally disadvantaged Nondisjunction oogenesis (XX + Y)

XXXXY - A rare form of Klinefelter’s Pentasomy 2N + 3 (autosomal = lethal) Polyploidy Mental deficiency Facial abnormalities Genital abnormalities

POLYPLOIDY - Semilethal Mosaic of two cell types - tetraploid (XXYY) and diploid (XY) The child died at nine months.

TETRAPLOID Cranial bone abnormalities, ocular anomalies & facial clefts Enlarged placenta Spleen, heart, kidneys, adrenal glands, brain anamolies

Aneuploidy One to a few chromosomes are lost or added to a normal set or nondisjunction (irregular distribution of sister chromatids (mitosis) or homologues (meiosis) Nullisomy - loss of one homologous pair 2N - 2 Monosomy - loss of a single chromosome 2N - 1 Trisomy - single extra chromosome; three copies of one chromosome type 2N + 1 Tetrasomy - an extra pair; four copies of one chromosome pair 2N + 2

Trisomy 21 Down’s Syndrome Trisomy - single extra chromosome; three copies of one chromosome type 2N + 1 Low IQ (variable) Epicanthal folds over eyes Short - broad hands with the simian line across the palms Below-average height

ICHTHYOSIS CONGENITA Brittle, leathery skin with deep bleeding fissures A recessive lethal allele with no obvious heterozygous phenotype. Similar in transmission to Tay-Sachs and Cystic fibrosis

NEUROFIBROMYLEYIS - von Recklinghausen disease Tumours in the central and peripheral nevous system Variable expressivity - degree of phenotype varies “Elephant Man” - John Merrick - London Hospital 1886

MARFAN SYNDROME A dominant collagen disorder Affects eyes, CV system, and the musculoskeletal system The silent killer

SEX - LINKED DISORDERS HEMOPHILIA The Royal Disease Colour blindness

CONJOINED TWINS An improper division of cells thought to occur embryonically somewhere between morula to blastula stage An environmental component?