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

1. sex cells (gametes: egg and sperm) SEXUAL Reproduction Requires: 1. sex cells (gametes: egg and sperm) 2. fertilization (when gametes combine) GENETIC DIVERSITY: produces a greater chance of variation within a species than asexual reproduction 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. MITOSIS Sexual reproduction results in offspring that are genetically different from the parent organisms. Needs 2 parents. MEIOSIS

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 IN ALL CELLS: Chromosome pairs 1-22 are autosomes. Chromosomes 23 are Sex-chromosomes X and Y, determine gender in mammals. XX = female XY = male

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

Now… MEIOSIS

MITOSIS MEIOSIS CELLS SOMATIC SEX CELLS (GAMETES NO. OF DAUGHTER CELLS 2 4 NO. OF CHROMOSOMES IN EACH DAUGHTER CELL DIPLOID (PAIR) HAPLOID (HALF) DIVERSITY GENETICALLY IDENTICAL DAUGHTER CELLS GENETICALLY DIFFERENT DAUGHTER CELLS WHEN THROUGHOUT ORGANISMS’ LIFETIME ONLY CERTAIN TIMES IN ORGANISMS’ LIFE CYCLE TYPE OF REPRODUCTION ASEXUAL SEXUAL

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

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)

MEIOSIS 1 IMPORTANT EVENTS: homologous chromosomes sister chromatids MEIOSIS I: PMAT 1 1. crossing over occurs during synapsis and the formation of tetrads (Prophase I) 2. pairs of homologous chromosomes separate (Anaphase I) Synapsis: pairing of homologous chromosomes forming a TETRAD (group of 4 chromatids)

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

MEIOSIS 2 IMPORTANT EVENTS: 1. SISTER CHROMATIDES separate during ANAPHASE 2 homologous chromosomes sister chromatids

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.