Do Now!!  How many chromosomes are in human non-sex cells? How about human sex cells? Where do we get those chromosomes from??

Meiosis!! Chapter 10

Meiosis Purpose: to make sex cells Male gamete= sperm Gamete: sex cell Male gamete= sperm Female gamete= egg (ovum)

Let’s define the following words… Meiosis: Sexual reproduction- production of gametes Gamete: Sex Cells (egg and sperm) Derived from germ cells Somatic Cells: Body Cells (non-sex cells)

Haploid: Diploid: Fertilization: Zygote: Half the chromosome number (n) Cells with 1 of each pair of chromosomes (23) Ex: Gametes Diploid: 2 of each type of chromosome (2n) Cells with twice the haploid number (46) Ex: Somatic cells Fertilization: Sperm enters egg Zygote: Fertilized egg (diploid)

Chromosomes and Chromosome Number Homologous chromosomes —set of chromosomes with same genes in same locations: Get one from each parent Same length Somatic cells: 46 chromosomes Gametes: 23 chromosomes

Karyotype Organized profile of a person’s chromosomes Autosomes (non-sex chromosomes): #’s 1-22 Sex chromosomes: #23 Monosomy: missing one chromosome Trisomy: 3 copies instead of 2

Do Now!!  If an organism is 2n=46, how many chromosomes are in the sex cells? What is monosomy? Trisomy? Define homologous chromosomes.

somatic cells (2n) gametes (n)

Meiosis Produces 4 daughter cells (NOT genetically identical!!!!!!) Like mitosis (PMAT), but 2 divisions: Meiosis I (separation of homologous chromosomes) Meiosis II (separation of sister chromatids) Produces 4 daughter cells (NOT genetically identical!!!!!!)

Interphase Same as Mitosis (G1, S, G2) DNA- Chromatin Centrioles- located near the nucleus Nucleolus is present

Prophase I Pairing of homologous chromosomes occurs forming a tetrad (Synapsis) The nuclear envelope breaks down/nucleolus gone Spindles form Crossing over takes place

Crossing over Homologous chromosomes exchange genetic material Recombination of genes between chromosomes How is crossing over related to genetic variation?

Metaphase I Chromosome centromeres attach to spindle fibers Homologous chromosomes line up at the equator

Anaphase I Homologous chromosomes separate and move to opposite poles

Telophase I The spindles break down Chromosomes uncoil, 2 new nuclei form The cell divides

Prophase II A second set of phases begins Chromosomes condense again Spindles form in each new cell

Metaphase II Chromosomes line up at metaphase plate of each cell

Anaphase II The sister chromatids are pulled apart at the centromere by spindle fibers Move toward the opposite poles of the cell

Telophase II The chromosomes reach the poles and the nuclear membrane and nuclei reform Spindles break down

Cytokinesis Cytokinesis results in four haploid cells (gametes) Each with n number of chromosomes. *So… if the original diploid cell has 10 chromosomes, how many will each gamete have? *Why are the gametes NOT genetically identical?

Do Now!!  Match the description to the phase of meiosis. 1. Sister chromatids are pulled apart. _____ A. Prophase I 2. Homologous chromosomes line up in the middle of the cell._____ B. Metaphase I 3. 2 daughter cells are formed ____ C. Telophase I 4. Nuclear membrane disappears__ D. Anaphase II 5. Nuclear membrane reforms around 4 cells ____ E. Anaphase I 6. Homologous chromosomes are pulled apart ____ F. Telophase II

Crash course biology!! https://www.youtube.com/watch?v=qCLmR9-YY7o

Spermatogenesis vs oogenesis

Genetic Variability Depending on how the chromosomes line up at the equator, four gametes with four different combinations of chromosomes can result. Genetic variation also is produced during crossing over and during fertilization, when gametes randomly combine.

Label the phases of meiosis