Chromosomes and Mieosis

Chromosome and Cell types Two main types of cells Body cells Also known as somatic cells (all cells in our body except sperm or eggs) Divide to make more by MITOSIS Sex cells Also known as gamete cells (sperm and eggs) Divide to make more by MEIOSIS

Chromosome and Cell types In humans, somatic cells have 23 pairs of chromosomes, meaning they have 46 total chromosomes. Somatic cells are DIPLOID cells (they have a full set of chromosomes)

In Mitosis, the daughter cells contain the same number of chromosomes as the parent cell

Chromosome and Cell types Gamete cells only have 1 of each chromosome 23 chromosomes Because sex cells only have HALF the number of chromosomes, they are called HAPLOID cells

Haploid and Diploid If a diploid cell had 20 chromosomes, how many chromosomes would be in the haploid cell?______ If a haploid cell had 12 chromosomes, how many chromosomes would be in a diploid cell?______ A muscle cell has 30 chromosomes. After mitosis, how many chromosomes do its daughter cells have?______ A cell has 22 chromosomes. After meiosis, how many chromosomes would it have?______ A muscle cell has 44 chromosomes. How many chromosomes would the sex cells have?______

Creating Cells for Sexual Reproduction Meiosis: Creating Cells for Sexual Reproduction

Meiosis Meiosis is the process by which sex cells are produced Similar to mitosis, however it includes TWO cell divisions resulting in 4 daughter cells with half the number of chromosomes.

MEIOSIS I: Homologous chromosomes separate MEIOSIS I: Homologous chromosomes separate INTERPHASE PROPHASE I METAPHASE I ANAPHASE I Centrosomes (with centriole pairs) Microtubules attached to kinetochore Metaphase plate Sister chromatids remain attached Sites of crossing over Spindle Figure 8.14 The stages of meiosis. Nuclear envelope Sister chromatids Tetrad Centromere (with kinetochore) Homologous chromosomes separate Chromatin

MEIOSIS II: Sister chromatids separate MEIOSIS II: Sister chromatids separate TELOPHASE II AND CYTOKINESIS TELOPHASE II AND CYTOKINESIS PROPHASE I METAPHASE II ANAPHASE II Cleavage furrow Sister chromatids separate Haploid daughter cells forming Figure 8.14 The stages of meiosis.

Prophase I Chromosomes are already copied Centrioles separate Nuclear membrane breaks down

Metaphase I Chromosome pairs line up next to each other

Anaphase I Chromosome pairs split Sister chromatids stay connected

Telophase I Cell starts to divide in two Nuclear membranes start to form again

Prophase II Cells have one set of sister chromatids Nuclear membrane breaks down Centrioles separate

Metaphase II Sister chromatids line up at the middle of the cell

Anaphase II Sister chromatids divide

Telophase II Cells start to split in two Each cell has one set of chromosomes—it is a haploid

Replicated chromosome Fig. 13-9a MITOSIS MEIOSIS MEIOSIS I Parent cell Chiasma Chromosome replication Chromosome replication Prophase Prophase I Homologous chromosome pair 2n = 6 Replicated chromosome Metaphase Metaphase I Anaphase Telophase Anaphase I Figure 13.9 A comparison of mitosis and meiosis in diploid cells Telophase I Haploid n = 3 Daughter cells of meiosis I 2n 2n MEIOSIS II Daughter cells of mitosis n n n n Daughter cells of meiosis II 22