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