Meiosis Summary DIRECTIONS Bb DIRECTIONS: Draw the parent cell before interphase Include a LONG pair of homologous chromosomes with 2 different colors Include a SHORT pair of homologous chromosomes with 2 different colors Color a small segment of one long chromosome with an allele of a contrasting color Color a small segment of the homologous long chromosome with a different allele of a contrasting color This makes a heterozygous genotype (Bb) B B b b b b

Meiosis Summary Bb B B b b b b One special parent cell divides twice into four egg cells or four sperm cells Each gamete (sex cell) will have half the number of chromosomes in parent cells and other normal cells The parent cell has two alleles (copies) for each gene. Alleles are short segments of the DNA that make up homologous chromosomes Each egg or sperm cell has one of the alleles from the parent cell B B b b b b

Interphase I Bb Interphase I Each chromosome is replicated to be become a pair of identical sister chromatids Each long chromatid has a copy of the allele from that chromosome The centrosome (centriole pair) is copied into two

Prophase I Prophase I The nuclear membrane has broken apart. Centrosomes move to opposite ends of the cell Spindle fibers from the centrosomes connect to the centromere on each chromatid. Spindle fibers pull the homologous chromatid pairs toward the center of the cell.

Metaphase I Metaphase I The chromatid pairs move along the spindle fibers into the middle of the cell. Chromatid pairs that are homologous to each to each other line up side by side along the center

Anaphase I Anaphase I Homologous pairs of sister chromatids separate from each other along spindle fiber towards opposite centrosomes. The cell continues to lengthen.

Telophase I Telophase I A nuclear membrane forms around each of the two sets of sister chromatid pairs in the cell. The cell has enlarged. In animals, the cell membrane begins to pinch inwards between the two nuclei.

Cytokinesis I B b Cytokinesis I in animal cells In animal cells, the cell membrane pinches inward until the two cells are separated. Each cell now has a different set of chromatid pairs in its nucleus Each cell now has long chromatid pairs with only one of the two alleles

Interphase II B b Interphase II Chromatids are NOT replicated during interphase II Centrosomes and other organelles are copied

Prophase II Prophase II The nuclear membrane in each cell has broken apart. Centrosomes move to opposite ends of the cell Spindle fibers from the centrosomes connect to the centromere on each chromatid. Spindle fibers pull the homologous chromatid pairs toward the center of the cell.

Metaphase II Metaphase II Chromatid pairs line up in the center of the cell

Anaphase II Anaphase II Identical chromatids separate from each other The centromere pulls each chromatid along the spindle fiber toward the centrosome

Telophase II Telophase II A nuclear membrane forms around each of the two sets of separated chromosomes in the cell. The cell has enlarged. In animals, the cell membrane begins to pinch inwards between the two nuclei.

Cytokinesis II b b B B b b Cytokinesis II In animal cells, the cell membrane pinches inward until the two cells are separated. Each of the two cells on the left now has an identical set of chromosomes in its nucleus Each long chromosome has one of the alleles from the parent cell Each of the two cells on the right now has an identical set of chromosomes in its nucleus Each long chromosome has the other allele from the parent cell