1. Meiosis & Sexual Life Cycles

3. Heredity Information  Genes – units of heredity  Section of DNA  Unique sequence of nucleotides  Program cells to synthesize particular proteins  Thousands per chromosome  Location of gene on DNA - locus

4. Reproduction Comparison  Asexual  One parent  Identical offspring  Mitosis  Sexual  Two parents Non-identical offspring Meiosis

6. Genetic Info  Chromosomes  46 in humans (23  Mom, 23  Dad)  22 are present in homologous pairs  Pair up based on length, centromere position, genes  Known as autosomes

8. A Karotype

9. Genetic Info  Last pair – sex chromosomes (X and Y)  Sperm & egg cells have 23 chromosomes  22 autosomes, 1 sex  Haploid number (n)  Made by meiosis  Fertilization (syngamy) makes zygote (fertilized egg) – now 46 chromosomes  Diploid (2n)

11. Life Cycle Varieties  Animals – picture A  Fungi & some algae – picture B

12. Life Cycle Varieties  Plants & some algae – picture C  Alternation of Generations Alternation of Generations  Multicellular diploid stage – sporophyte  Meiosis makes haploid spores  Spore goes through mitosis – makes haploid multicellular – gametophyte  Gametophyte makes gametes by mitosis  Fertilization makes zygote, which becomes sporophyte

15. Meiosis – Let’s InvestigateLet’s Investigate  One replication, two consecutive divisions  Result – 4 haploid daughter cells  Figure of meiosis steps in text – STUDY

18. Terms to know  Synapsis – pairing up of homologous chromosomes  Tetrad – pair of homologous chromosomes  Crossing over of non-sister chromatids – chiasmata (chiasma) Crossing over  Results in variations

19. How Do We Get Variety?  Independent Assortment of Chromosomes Independent Assortment of Chromosomes  Before meiosis, how chromosomes line up on metaphase plate is random  Each pair is independent  Metaphase I for tetrad; metaphase II for chromatids  Results in many combinations of chromosomes in gametes (8 million possibilities)

21. How Do We Get Variety?  Crossing Over  Prophase I  Homologous chromosomes exchange segments of information from non-sister chromatids  Humans average 2-3 crosses per pair

23. How Do We Get Variety?  Random Fertilization  Random sperm – 8 million possibilities  Random egg – 8 million possibilities  Result – 1 zygote of over 70 trillion without any crossing over