Meiosis (2)

meiosis

cell division for sexual reproduction

Sister chromatids

hold two identical copies of a chromosomes made during S-phase

homologues / homologous pairs

maternal chromosome, paternal chromosome

meiosis location in males

gonad: testies

meiosis location in females

gonad: ovaries

sex cell: male gamete

sperm

sex cell: female gamete

egg

Why do these cells need to be created? (a.k.a. the point of meiosis)

to make genetically unique haploid cells

haploid

(n), 1 complete set of chromosomes, sex cells

diploid

(2n), 2 sets of chromosomes, all cells except sex cells

crossing over

mixing alleles between homologus partners(maternal/paternal) → making genetically unique cells in prophase 1

Meiosis I, Prophase I, step 1

nuclear membrane breaks down, centrioles move on opposite sides of cell, spindle fibers form, sister chromatids condense and cross over

Meiosis I, Metaphase I, step 2

homologues chromosomes line up in middle in TWO rows

Meiosis I, Anaphase I, step 3

homologues separate and move away from one another (up/down)

Meiosis I, Telophase I, step 4

chromosomes unwind, nuclear membrane form on each offspring nucleus

Meiosis II, Prophase II, step 5

no crossing over, chromosomes in daughter cells condense, spindle form

Meiosis II, Metaphase II, step 6

sister chromatids line up in ONE row

Meiosis II, Anaphase II, step 7

sister chromatids ripped apart, haploid unduplicated

Meiosis II, Telophase II, step 8

four haploid cells, won’t ever go through meiosis but only mitosis

How is meiosis in female animals different than “general” meiosis

cytokinesis happens unevenly, not much cytoplasm goes into each daughter cells causing one large egg and a small egg, a polar body, to then degrade