1. CHAPTER 13 SEXUAL LIFE CYCLES: MEIOSIS

2. 13.1 OFFSPRING ACQUIRE GENES FROM PARENTS BY INHERITING CHROMOSOMES

3. WHERE DO YOUR GENES COME FROM? Ever wonder where you got your traits from? And where they got their traits from?

4. WHAT’S A GENE? A segment of DNA which codes for a protein Can code for an enzyme, a structural protein or a regulatory protein This determines an organism’s traits More next unit…

5. ASEXUAL REPRODUCTION No gametes produced One parent Prokaryotes – binary fission Single-celled eukaryotes Yeast – budding Amoeba – binary fission Simple multicellular eukaryotes Hydra – budding Complex multicellular eukaryotes - regeneration Sea stars Planaria Little to no genetic variation

6. SEXUAL REPRODUCTION Gametes produced by meiosis Two parents Direct contact not required Plants: pollination strategies vary Animals: release of gametes into environment (aquatic) Many sources of genetic variation

7. 13.2 FERTILIZATION AND MEIOSIS ALTERNATE IN SEXUAL LIFE CYCLES

8. HOMOLOGOUS CHROMOSOMES Paired chromosomes Both chromosomes carry a pair of genes Control same inherited characters Homo logous = same information One from each parent Autosome Chromosome 1-22 (everyone has) Sex chromosome Chromosome 23 (XX = female, XY= male)

9. CHROMOSOME NUMBER BY CELL TYPE Somatic cell Body cell Diploid Contains 2 sets of homologous chromosomes (2n) Gamete Reproductive cell (sperm or egg) Haploid Contains 1 set of homologous chromosomes (1n) Diploid Haploid

10. SEXUAL LIFE CYCLES Alternating processes, alternating stages Meiosis reduces chromosome number Diploid  Haploid 2n  n Humans 46  23 Fertilization restores chromosome number, forms zygote Haploid  Diploid n  2n Necessary for sexually reproducing organisms to produce gametes

11. 13.3 MEIOSIS REDUCES THE NUMBER OF CHROMOSOMES FROM DIPLOID TO HAPLOID

12. STAGES OF MEIOSIS Meiosis I Interphase Prophase I Metaphase I Anaphase I Telophase I Meiosis II Prophase II Metaphase II Anaphase II Telophase II 1 st division of meiosis separates homologous pairs 2 nd division of meiosis separates sister chromatids *just like mitosis* DNA replication

14. 13.4 GENETIC VARIATION PRODUCED IN SEXUAL LIFE CYCLES CONTRIBUTES TO EVOLUTION

15. INDEPENDENT ASSORTMENT Random orientation of homologues at metaphase plate during metaphase I Independent assortment in humans produces 2 23 (8,388,608) different combinations

16. CROSSING OVER During Prophase I Homologous pairs swap pieces of chromosome Sister chromatids intertwine and cross over each other Breakage and re-fusing of DNA Creates completely new combinations of traits in the next generation

17. RANDOM FERTILIZATION Random ovum fertilized by a random sperm Any 2 parents will produce a zygote with over 70 trillion (2 23 x 2 23 ) diploid combinations

18. SEXUAL REPRODUCTION CREATES VARIABILITY Allows us to maintain both genetic similarity and differences Why is this significant to evolution by natural selection?