MISTAKES IN MEIOSIS

MISTAKES IN SEPARATION Aneuploidy: Error during meiosis Separation of chromosomes doesn't take place properly resulting in cells have too many or too few chromosomes Caused by: NONDISJUNCTION -Failure of homologous chromosomes to separate in meiosis I -Failure of sister chromatids to separate in meiosis II

EXAMPLES MONOSOMY: Sex cell missing one chromosome (in place of a homologous pair) POLYSOMY: Condition where there are more chromosomes than required (in place of a homologous pair) POLYPLOIDY: Non-disjunction of all of the chromosomes in a gamete that unites with a haploid gamete to produce 3 sets of chromosomes (3n)

MISTAKES IN CROSSING OVER Pieces of genetic information are exchanged but do not re-attach properly Deletion: When exchanged information does not reattach to the chromosome Inversion: Segment of DNA reattaches to chromosome but in the reverse order Duplication: The exchanged information is repeated on the chromosome Translocation: Movement of information from one chromosome to a non-homologous chromosome

KARYOTYPES: A karyotype is an organized picture of a person’s chromosomes Test to examine chromosomes Can help identify genetic problems by: Counting the number of chromosomes (too many or too few) Looking for structural changes in chromosomes The test can be performed on almost any tissue: Amniotic fluid Blood Bone marrow Tissue from the placenta

KLINEFELTER SYNDROME Not inherited Genetic Changes: Male with extra copy of X chromosome (XXY) Problem: Nondisjunction causes polysomy Symptoms: -Low levels of testosterone -Breast development -Decreased body and facial hair -Abnormal sexual development -Learning disabilities

TURNER SYNDROME Not inherited Genetic Changes: Note - cannot have Y0, fetus will not survive TURNER SYNDROME Not inherited Genetic Changes: Missing/damaged X chromosome (X0) Problem: -Monosomy caused by nondisjunction -Deletion or inversion Symptoms: -Shorter -Webbed neck -Skeletal abnormalities -Heart defect -Kidney problems

TRIPLE X: Not inherited Genetic Changes: Female with 3 X chromosomes (XXX) Problem: Nondisjunction causes polysomy Symptoms: Taller Increased incidence of learning disabilities Normal otherwise

47 XYY Not inherited Genetic Changes: Extra Y chromosome in males (XYY) Problem: Nondisjunction causes polysomy Symptoms: Taller No physical problems Some risk of learning disabilities