Abnormal Meiosis: Genetic Disorders

Review: Human Chromosomes  There are 46 chromosomes (23 homologous pairs) in each somatic cell  22 pairs of autosomes  1 pair of sex chromosomes XX = Female, XY = Male  Karyotype – picture of chromosomes arranged according to shape and size

Normal Meiosis 46 23

Non-disjunction  “not coming apart”  failure of chromosome pairs to separate properly during cell division  produces gametes with 22 or 24 chromosomes  due to a failure of homologous chromosomes to separate in meiosis I, or the failure of sister chromatids to separate during meiosis II or mitosis  Results in a cell with an imbalance of chromosomes

Abnormal Meiosis I ALL 4 Abnormal

Abnormal Meiosis II Sister chromatids fail to separate

Abnormal Meiosis  If the error occurs in meiosis I, ALL 4 of the gametes will be abnormal  If the error occurs in meiosis II, TWO of the gametes will be normal, and the other 2 gametes will be abnormal.

Trisomy Examples  Down syndrome (chromosome 21)  Edwards syndrome (chromosome 18)  Patau syndrome (chromosome 13)  Klinefelter syndrome (XXY, XXYY, XXXXY)

Down syndrome

Down Syndrome  1 in 800 live births  Mild to moderate intellectual ability  Round, full face  Short height  Large forehead

Down Syndrome

Edwards Syndrome 1 in 4,400 births XX=80% XY=20%

Edwards Syndrome Small head Developmentally delayed Internal organ abnormalities 90% die before 5 months of age

Patau Syndrome

Small head Small or missing eyes Heart defects Extra fingers Abnormal genitalia Developmentally delayed Most die a few weeks after birth Patau Syndrome

Klinefelter Syndrome

 1 in 1000 live births  Males are sterile  Small testes; shortage of testosterone  Breast enlargement, reduced facial and body hair  Some boys are shy and/or have learning disabilities

Prenatal testing

Structural Abnormalities  Mutation: any change to the DNA of a cell Deletions: A portion of the chromosome is missing or deleted  e.g. Wolf-Hirschhorn syndrome, and Jacobsen syndrome

Structural Abnormalities Duplications: A portion of the chromosome is duplicated, resulting in extra genetic material  e.g. Charcot-Marie-Tooth disease type 1A

Structural Abnormalities Translocations: When a portion of one chromosome is transferred to another chromosome

Structural Abnormalities continued…  Inversions: A portion of the chromosome has broken off, turned upside down and reattached, therefore the genetic material is inverted

Please Complete  Computer activity  Check and Reflect Sheet