1. Genetic Continuity: What does it mean? “Reproduction of offspring with the same features as the parent” Every new cell needs to have an exact copy of its parents DNA. New exact copies are created when cells reproduce. Chromosomes and Cell Reproduction

2. The Cell Cycle The life of a cell is composed of 2 main parts: 2) Mitosis: Series of events that make up the reproductive stage of cell life. 1) Interphase: the non-reproductive stage where cell undergoes normal cell function.

3. Mitosis Interphase Cycle Start Cycle End

4. Interphase: non-reproductive portion of cell cycle -cell organelles are also duplicated -nuclear material (DNA) is duplicated during late interphase -cell undergoes normal functions WHY are the DNA and organelles duplicated?

5. Interphase Animal Plant

6. Prophase: the start of mitosis -spindle fibers form, will anchor chromosomes to poles of cell -chromosomes coil thicker,shorter -nuclear membrane breaks down Why does the nuclear membrane need to break down? Why does DNA have to form chromosomes for cell division?

7. Prophase Animal Plant

8. Metaphase: -centromere of each chromosome firmly attaches to spindle fiber -chromosome pairs migrate toward equator of cell What is the purpose of a centromere?

9. Metaphase AnimalPlant

10. Anaphase: -in plants, new cell wall starts to form, called the “cell plate” -cell membrane begins to pinch inward -replicated chromosomes move apart -centromeres split

11. Anaphase Animal Plant

12. Telophase: -chromosomes uncoil, become longer and thinner again. -cell division is almost complete -spindle fibers dissolve -cytokinesis begins

13. Telophase Animal Plant

14. Cytokinesis: -the cytoplasm of the cells is divided. -new cell membrane is formed, and encloses both cells. -two genetically identical “daughter cells” are formed -in plants, new cell wall is complete

15. Chromosome Number -Each species of organism has a specific number of chromosomes. Example: Humans have 46 chromosomes, Fruit flies have 8 chromosomes

16. Most organisms have their chromo- somes arranged in pairs. The diploid number of chromosomes is represented by 2n, where n is the number of different pairs of chromo- somes Cells with 2 of each chromosome are called diploid.

17. Example: Humans have 46 chromosomes, arranged in 23 pairs. n=23, so 2n= 46 Fruit flies have 8 chromosomes, arranged in 4 pairs. n= 4, so 2n=8

18. In diploid cells, each member of a pair has the same basic structure. The 2 members of a pair are called homologs, and the pair is called a homologous pair

19. Example: Each member of a homologous pair may carry the gene for eye color: The combination of both genes will determine the trait that is expressed. 1 member may carry the gene for blue eyes, the other member may carry the gene for brown eyes.

20. Normal Male Human Karyotype

21. Meiosis: Cell division that reduces the chromosome number by 1/2. The result is cells with the haploid number of chromosomes.

22. The haploid number is represented by n. The haploid number is 23. Example: In humans, the diploid number is 2n, or 46

23. Meiosis makes it possible for sexual reproduction, and therefore the recombination of genes, to occur. Sex cells are called gametes, and are either sperm from males, or eggs (ovum) from females. Sperm and eggs are both haploid.