Meiosis Notes 1 Ch 10 -11 Meiosis

Parent can produce many types of offspring . Families will have resemblances, but no two are exactly alike

Every cell has a nucleus Every nucleus has chromosomes The number of chromosomes depends on the species Ex: Humans Chimpanzee 48 have 46 Chicken 78 have 46 Frog 26 Pea 14

Genes control the TRAITS of the individual Genes are located on chromosomes Genes control the TRAITS of the individual

Chromosomes come in matching sets-these are called homologous pairs Same length Same centromere position Carry genes that control same inherited traits

Cells in your body have a complete set (all 46) - they are called DIPLOID (2n) Sex Cells ( sperm and egg) only have half (23) – they are called HAPLOID (n) Gametes: sex cells that have half the number of chromosomes

Meiosis Cell division that reduces the # of chromosomes Occurs in reproductive structures Reduces chromosome # through separation of homologous chromosomes

Objective: List the stages of meiosis and what is happening in those stages Warm Up: List this stage of mitosis and explain what is happening here.

Interphase Replication of DNA Synthesis of proteins

Prophase I Chromatids match up with their Homologous pairs and fasten together in a process called synapsis. Crossing over: Trade gene segments between the pair of homologous chromosomes. (exchange genetic material) EXTREMELY IMPORTANT!! THIS IS THE PHASE WHERE CROSSING OVER CAN OCCUR

Metaphase I The homologous chromosomes line up as pairs at the equator. * diff from mitosis

Anaphase I Homologous pairs separate Still consist of 2 sister chromatids

Telophase I Consist of 2 sister chromatids The cytoplasm divides, forming two new daughter cells. end of the first meiotic cell division. Each of the newly formed cells has half the number of the parent cell’s chromosomes, but each chromosome is already replicated ready for the second meiotic cell division

Cytokinesis Occurs simultaneously with telophase I Forms 2 daughter cells

Prophase II Chromosome condense Spindle apparatus form

Metaphase II Haploid # of chromosome line up at the equator

Anaphase II Sister chromatids pulled apart at the centromere by spindle fibers and sister chromatids move toward opposite poles of the cell

Telophase II Chromosome reach the poles Nuclear membrane and nuclei reform

Cytokinesis Results in 4 haploid cells (n)