Meiosis What is Meiosis The process that produces

Meiosis

What is Meiosis? The process that produces haploid gametes in diploid organisms. Cells produced only contain ½ number of chromosomes. Haploid cell = n Diploid = 2 n

What are gametes? Sex cell; a haploid egg or sperm.

Describe haploid Contains only a single set of chromosomes or single set of genes. Remember you get one set of genes from your mother the other set from your father. Diploid-contains both sets of chromosomes.

What is difference between Meiosis and Mitosis? In meiosis, a cell undergoes two consecutive divisions, called meiosis I and meiosis II. Four genetically different daughter cells result from these divisions. Meiosis produces sex cells. In mitosis, a cell undergoes one cell division and two genetically identical cells result. Mitosis produces somatic (body) cells.

What are the stages of Meiosis? Meiosis I Prophase I Metaphase I Anaphase I Telophase I Meiosis II Prophase II Metaphase II Anaphase II Telophase II

Prophase I Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. During prophase I homologous chromosomes may cross over and exchange portions of their chromatids. This process is called crossing over.

What is a homologous chromosome? Two chromosomes that make up a matched pair in a diploid cell. One homologous chromosome is inherited from the organism’s mother, the other from the organism’s father.

What is a tetrad? A paired set of homologous chromosomes, each composed of two sister chromatids.

Metaphase I Spindle fibers attach to the chromosomes and tetrads line up in the center of the cell.

Anaphase I The fibers pull the homologous chromosomes toward opposite ends of the cell.

Telophase I Nuclear membranes form. The cell separates into two haploid cells.

Cytokinesis I Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original cell.

Prophase II The DNA coils back up around the proteins forming chromosomes. The nuclear membrane dissolves The spindle fibers reform

Metaphase II The chromosome line up in a similar way to the metaphase stage of mitosis.

Anaphase II The sister chromatids separate and move toward opposite ends of the cell.

Telophase II Meiosis II results in four genetically different haploid (N) cells.

Accidents that can occur during Meiosis Nondisjunction – Members of a chromosome pair fail to separate during anaphase. This results in diploid gametes. Crossing over, that sometimes occur during Prophase I, can cause this. Examples: Trisomy 21(Down’s syndrome) and Klinefelter syndrome.

What alterations of chromosome structure (mutations) could lead to birth defects and cancer? Deletion- When a fragment of a chromosome is lost. Duplication- When a fragment from one chromosome joins to a homologous chromosome. Inversion- When a fragment reattaches to the original chromosome but in the reverse direction. Translocation- the attachment of a chromosomal fragment to a nonhomologous chromosome.

Quiz Name 2 ways in which meiosis differ from mitosis? What is a gamete? What does haploid mean? If a human skin cell contains 46 chromosomes, how many chromosomes would a human sperm cell contain?

Quiz If a human skin cell contained 46 chromosomes, how many chromosomes would a human liver cell contain? What types of accidents can occur in Meiosis? What is crossing over? When does it occur? Name and describe one alteration of chromosome structure.