Mutations Chromosomal Mutations (errors of cell division) Point Mutations (errors of DNA replication)

Part 1: Chromosomal Mutations Errors of Cell Division

Karyotypes Photograph of chromosomes, arranged by homologous pairs First 22 pairs (in humans) are “autosomes”. Last pair are sex chromosomes XX = female, XY = male

Down Syndrome Female 47 XX +21 Aneuoploidy Cells that have an abnormal number of chromosomes are aneuploid. Normal Female 46 XX Down Syndrome Female 47 XX +21

Some Common Aneuoploidies X X X Turner’s Syndrome 45 X Triple X Syndrome 47 XXX

More Common Aneuoploidies X X Y X Y Y Klinefelter’s Syndrome 47 XXY XYY Syndrome 47 XYY

Anuoploidy Results from Nondisjunction of Sister Chromatids, During Mitosis or Meiosis

Errors Occur in Mitosis and Meiosis Errors of Mitosis Errors of Meiosis Errors of mitosis are confined to daughter cells (not hereditary) Called “somatic mutations” Errors of meiosis are passed to every cell of an offspring Called “germ line mutations”

Nondisjunction Nondisjunction is the failure of chromosomes to separate during cell division, leading to asymetrical distribution between daughter cells.

Nondisjunction (continued) Most chromosomal mutations of mitosis or meiosis are due to nondisjunction of sister chromatids, during anaphase (anaphase II in meiosis) Additionally, in meiosis I, nondisjunction may occur between homologous chromosomes

Somatic Mutation Somatic mutations occur in body (somatic) cells and affect only the daughter cells of the affected cell. Moles and some cancers are the results of somatic mutations.

Nondisjunction can occur when spindle fibers from one centriole attach to both sister chromatids (mitosis & meiosis II) or both homologous chromosomes (meiosis I) Spindle fibers from one centriole attaching to both sister chromatids

Mitosis: Metaphase Homologous chromosomes Sister chromatids

Chromosomes align across the “equator” of the cell, one sister chromatid on each side.

Mitosis: Anaphase Nondisjunction of sister chromatids

Mitosis: Telophase & Cytokinesis Nuclei form

Interphase Daughter cells are aneuoploid Karyotype: 2n + 1 (trisomy) (monosomy)

Germ Line Mutation Errors that occur in gamete production affect offspring.

Meiosis I: Metaphase Homologous chromosomes line up across the middle Sister chromatids

Meiosis I: Anaphase Nondisjunction causes both homo chromo’s to be in one cell

Meiosis I: Telophase

End of Meiosis I 2 aneuoploid daughter cells formed

Meiosis II: Prophase

Meiosis II: Metaphase Chromosomes line up at “equator” of cell.

Meiosis II: Anaphase Sister chromatids separate to opposite sides of cell.

Meiosis II: Telophase 4 aneuoploid haploid cells form (sperm or eggs)

Meiosis II: Telophase Karyotype N - 1 Karyotype N + 1

Errors of DNA Replication Part 2: Point Mutations Errors of DNA Replication

Single Nucleotide Substitution

Deletion

The fat cat ate the big rat. The frt cat ate the big rat. The ftc ata tet heb igr at…..