Reproduction, Mitosis, Meiosis Reproduction can be: SEXUAL OR ASEXUAL Asexual Reproduction: requires only 1 parent offspring are exact copy of the parent: a clone No genetic variety in the population: organisms are “copies” of the original. Example: Binary Fission divide into two equal halves Single cell organisms

Sexual Reproduction Requires sex cells (gametes, egg and sperm) Requires fertilization (when gametes combine) produces a greater chance of variation (diversity) within a species than asexual reproduction would. improves the chances that a species will adapt to his environment and survive.

Sexual vs. Asexual Reproduction Asexual reproduction results in offspring that are genetically identical to the parent organism. Needs 1 parent. Sexual reproduction results in offspring that are genetically different from the parent organisms. Needs 2 parents.

First… Chromosomes

X and Y, determine gender in mammals. Chromosomes and Meiosis two types of chromosomes: Autosomes found in body cells (diploid, 2 copies, 2N) sex chromosomes found in sex cells (haploid, 1 copy, N) Humans: body cells have 23 pairs or 46 (2N) chromosomes Sex cells have 23 (N) chromosomes X and Y, determine gender in mammals. XX = female XY = male Chromosome pairs 1-22 are autosomes.

same pair. Same size Same shape BUT NOT IDENTICAL: genes are different versions of the same trait! Ex. Eye color

Now… MEIOSIS

Mitosis - occurs in somatic cells makes 2 diploid cells Produces genetically Identical cells Meiosis occurs in sex cells (gametes) makes 4 haploid cells produces genetically different cells

DIPLOID DIPLOID MEIOSIS SPERM EGG (HAPLOID) (HAPLOID) DIPLOID

PMAT I: prophase 1 metaphase 1 anaphase 1 telophase 1 Main Events: 2 PARTS IN MEIOSIS: homologous chromosomes sister chromatids MEIOSIS I PMAT I: prophase 1 metaphase 1 anaphase 1 telophase 1 Main Events: crossing over occurs (Prophase I) pairs of homologous chromosomes separate (Anaphase I) MEIOSIS II PMAT II: prophase 2 metaphase 2 anaphase 2 telophase 2 - Main Event: sister chromatids separate (Anaphase 2)

Meiosis I MEIOSIS I Chromosomes condense Crossing over occurs during synapsis (when chromosomes pair up to exchange pieces) Chromosomes exchange pieces Creates genetic variation Chromosomes line up in the middle of the cell Chromosomes move randomly to separate cells Independent assortment! Chromosomes are placed into two daughter cells MEIOSIS I Meiosis I Chromosome number is reduced ! Cells are now haploid (n)

SYNAPSIS

Chromosomes stay condensed Cells undergo a second division Chromosomes line up in middle of cells Chromatids move apart from each other One chromatid from each chromosome gets placed in a separate cell 4 genetically different haploid cells are produced MEIOSIS II

Sources of Genetic Variations in Meiosis Crossing over In Prophase 1 Homologous chromosomes exchange pieces Independent Assortment In Anaphase 1 Chromosomes move randomly to different cells . Fertilization “Which sperm gets to the egg first?” – this is random, and generates variations in the offspring.