Bell-Ringer (discuss with a partner)

1. Bell-Ringer (discuss with a partner) • Where do you think cells get their instructions that enable different cells to perform their duties? • What is a physical human trait? • What causes our traits to manifest themselves?

2. Discussion Questions • What did the pipecleaners represent? • What did the beads represent? • What are some more widely-shared traits among humans which we did not represent in this activity? • What are some advantages or disadvantages to being a multicellular organism? • Humans inherit 23 chromosomes form their mother and 23 from their father. Do all organisms inherit 23 chromosomes from their mother and 23 from their father? • What are examples of other observable human traits? What are examples of non-observable human traits? • Why would a scientist study high frequency traits in the human population?

3. Chromosomes Chapter 12 AP BIOLOGY Ms. Springstroh Adapted from Ms. Gaynor

4. 100 µm (a) Reproduction. An amoeba, a single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism (LM). Figure 12.2 A Why is Cell Division Important? • Unicellular organisms • Reproduce by cell division  increasing the population.

5. 200 µm 20 µm (b) Growth and development. This micrograph shows a sand dollar embryo shortly after the fertilized egg divided, forming two cells (LM). (c) Tissue renewal. These dividing bone marrow cells (arrow) will give rise to new blood cells (LM). Why Do Multicellular Organisms Depend on Cell Division? • Development & Growth • Repair (ex: tissue renewal)

6. Organization of the Genetic Material • All of a cell’s DNA (genetic information) is called its genome • In prokaryotes • Genome=single, long DNA molecule in a circle • In eukaryotes • Genome = several DNA molecules grouped in clumps (called chromosomes)

7. DNA Molecules • DNA (in nucleus of eukaryotes) can be in 2 forms • Chromatin: DNA is not tightly packed together (loosely coiled) • Occurs during interphase • Chromosomes: tightly packed together (TIGHTLY coiled) • Occurs during mitosis (cell division)

8. Tightly coiled? Not tightly coiled?

10. How Does DNA Fit into a Small Cell? • Prokaryotic organisms • No nucleus; instead have a nucleiod region • DNA = 1 chromosome

11. How Does DNA Fit into a Small Cell? • Eukaryotic organisms split their DNA into several pieces (called chromosomes) • stored within the cell's nucleus • DNA is coiled around proteins known as histones

12. DNA + histones  form nucleosomes(help to “super coil” DNA)

13. Cell Division (aka Mitosis) • Makes 2 genetically identicaldaughter cells from 1 parent cell • Before cells divide • They duplicate their genetic material  ensures that each daughter cell receives an exact copy of the genetic material, DNA

14. Making Chromosomes **Occurs right before cell division (mitosis) Steps: • DNA copies itself through DNA Replication • The DNA coils (wraps) around proteins called histoneproteins. • Chromosomes are made.

15. 50 µm The DNA molecules in a cellAre packaged into chromosomes

16. Chromosome Structure • Two shapes of chromosomes • Single chromosome (1 copy of DNA); “V” shaped; a.k.a. chromatid • Double Chromosome (2 copies of DNA); “X” shaped; a.k.a-duplicated chromosome Occurs right before cell division (mitosis)

17. Chromosomes and Cell Division • In preparation for cell division (mitosis) • DNA is replicated (single  double chromosome) • V shape  X shape

18. 0.5 µm A eukaryotic cell has multiplechromosomes, one of which is represented here. Before duplication, each chromosomehas a single DNA molecule. Chromosomeduplication(including DNA synthesis) Once duplicated, a chromosomeconsists of two sister chromatidsconnected at the centromere. Eachchromatid contains a copy of the DNA molecule. Centromere Sisterchromatids Separation of sister chromatids Mechanical processes separate the sister chromatids into two chromosomes and distribute them to two daughter cells. Sister chromatids Centromeres Figure 12.4 Each duplicated chromosomehas two sister chromatids, which separate during cell division Sister chromatids: replicated forms of a chromosome which divide from one another during cell division

19. Double Chromosome Structure Kinetochore attaches to spindle fibers Sister

20. Another view…

21. Chromosomes • Every eukaryotic species has a characteristic, unique # of chromosomes inEACH cell nucleus • Ex: Humans have 46 chromosomes • # of chromosomes does NOT necessarily equal complexity

22. Different Types of Cells • There are 2 types of cells in the human body • Somatic cells: all body cells 2. Gametes: reproductive cells (sperm and egg)

23. Different cell types  different cell divisions • Eukaryotic cell division consists of • Mitosis, division of the nucleus • Cytokinesis, division of cytoplasm • Occurs in somatic cells • In meiosis • Gamete cells are produced after a reduction in chromosome number • Occurs in gametes

24. Chromosome Number • Gametes (sperm/egg) have 1 copy of each chromosome and are called haploid. • Somatic (body) human cells have 2 copies of each chromosomes and are called diploid. • Human somatic cells have 23 PAIRS of chromosomes (total 46 chromosomes). • All pairs of chromosomes differ in size, shapes, and set of genes.

25. Haploid vs. Diploid • Haploid= when a cell has 1 copy of each chromosome. • Expressed as n • In humans: n= 23 • Diploid= when a cell has 2 copy of each chromosome. (a.k.a TOTAL # of chromosomes in organisms) • Expressed as 2n • In humans: 2n = 46 n Haploid sperm cell Haploid egg cell n Fertilization 2n Diploid Zygote cell

26. Set of Chromosomes • Each chromosome set contain 2 “homologues.” • Chromosomes have a “twin” or matching pair. • Homologous Chromosomes= chromosomes that are similar in shape, size, and genes. • Each homologue in a pair comes from eachparent!