It’s MEIOSIS!

Vocab.. Cell cycle: Interphase (G1, S, G2), mitosis (cell division) and cytokinesis (pinching off into two cells) Mitosis- division of cells producing 2 IDENTICAL cells (somatic or autosome cells – skin, heart, liver) Gamete- sperm and egg Zygote- fertilized egg cell Haploid- half chromosomes (23) Diploid- all chromosomes (46) Chromosome- 2 chromatids (strands) and centromere (center)

Mitosis Review Prophase- start to divide Metaphase- line up in middle Anaphase- centromeres break apart Telophase- everything is identical on both ends and starts to form into two Cytokinesis- final pinching off of 2 identical cells ** remember mitosis produces identical cells, so each parent cell has 46 chromosomes, baby has 46 chromosomes***

Meiosis Meiosis- division of sex cells (sperm and egg) Produces gametes with half the number of chromosomes so when baby forms he/she has half from mom and half from dad

Meiosis Process Involves 2 divisions: meiosis 1 and meiosis 2 (each broken into PMAT)

Starts with homologous pairs that DO NOT break apart until meiosis 2 Results in 4 haploid cells, each having half the number of chromosomes (zygote- half from mom and half from dad)

Meiosis contributes to genetic variation 1) Independent assortment- random homologous chromosomes

2) Crossing over Prophase 1- crossing over occurs (portion of one chromosome switcher onto another, producing diversity)

3) Random fertilization The sperm that fertilizes the egg is simply by chance

Importance of genetic variation Meiosis is essential to evolution- No genetic process generates variation more readily Pass on learned traits Creates diversity

Meiosis results in gametogenesis Gametogenesis- formation of gametes

Spermatogensis Spermatogenesis- formation of male sperm Diploid cell increases in size and shape and becomes a large immature cell called a germ cell Cell undergoes meiosis 1 resulting in 2 cells 2 cells undergo meiosis 2 forming 4 haploid cells ALL 4 of the haploid cells grow a tail and become sperm Each sperm is genetically different Sperm is produced throughout a man’s reproductive years

Oogenesis Oogenesis- forming eggs in female During meiosis 1 the cytoplasm divides unevenly, one cell gets most of the cytoplasm and this will become the EGG Larger cell undergoes meiosis 2, division is uneven again, the larger cell becomes an ovum Ovum- egg ready for fertilization Other cells produced become polar bodies- cells that just get reabsorbed into the human body

Oogenesis continued Egg development begins before birth, during embryonic development cells divide by mitosis to produce 2 million immature egg cells Ovaries of a newborn contain all the eggs a female will ever have During puberty egg cells complete meiosis 1 Once egg is fertilized, egg undergo meiosis 2

Reproduction Two types: Asexual reproduction- 1 parent a. produces clones b. prokaroytes (bacteria)- binary fission c. eukaryotes - fragmentation (planaria) body breaks into two pieces and develop - budding (hydra) new offspring splits from existing one

Fragmentation (planaria)

Budding (hydra)

2) Sexual Reproduction- - two parents forming haploid gametes combine to form a fertilized egg (zygote) - offspring has a combination of traits from mom and dad

Sexual versus Asexual Pro - produce many organisms in a short time Con Asexual Reproduction Pro - produce many organisms in a short time Con - no variation, can NOT adapt Sexual Reproduction Pro - different combination of genes, able to adapt Con - long period of time