1. Chapter 6 Chromosomes & Cell Reproduction 6.1 Chromosomes

2. New Cells formed by cell division Has anyone ever fallen and scraped their knee? What happened next? What happens about a week later?

3. New Cells How do we get these new cells? Where do they come from? Cells are made by existing cells in a process called cell division. Take a guess on how many cells are produced by a human body everyday. 2 Trillion That makes 25 million every second.

4. Why Cell Division? Eukaryotic organisms undergo cell division for many different reasons. Growth Development Repair Production of new cells Sex cells, or gametes, undergo a different type of cell division which gives half of the amount of genetic material. Gamete – Reproductive cells (Sperm & Egg)

5. Division of Bacterial Cells Bacterial cells divide differently than eukaryotic cells. Prokaryotic cells undergo binary fission which is a form of asexual reproduction that produces an identical offspring. The parent passes an exact copy of its DNA to it offspring… like a clone.

6. Binary Fission Step 1: DNA is copied Step 2: Cell divides. Each cell has a copy of DNA.

7. Division of Eukaryotic Cells Eukaryotic cell division is quite a bit different. Eukaryotic cells are very complex and a vast amount of genetic information is encoded in its DNA. Because there is so much genetic information that all needs to be divided up properly, eukaryotic cells bunch their DNA into nice organized structures called chromosomes.

8. Chromosomes Chromosome – A structure made of DNA coiled around proteins.

9. Chromosomes Cont. Chromosomes are made of two chromatids that are attached at a midpoint called a centromere. Humans have 23 pair of chromosomes. Each pair are called homologous chromosomes, chromosomes that are similar in shape, size & genetic content. One set of chromatids come from the sperm & the other from the egg.

10. Chromosome numbers All of the cells other than the sex cells are called diploid. A cell that contains two sets of chromatids. Sex cells are called haploid cells. Cells that contain only one set of chromatids. Haploid = 1n Diploid = 2n n = a variable, for instance in humans n = 23

11. The romance of gametes When two gametes or haploid cells come together a zygote is formed. Zygote – a fertilized egg cell. The first cell of a new individual. 1n + 1n = total chromosome number Eg. 23 + 23 = 46 chromosomes Females send an X chromosome & males send either an X or a Y

12. Chromosome numbers Do you think that every organism has the same number of chromosomes? Eg. A fruit fly only has 4 chromosomes. Why so little?

13. Karyotyping Karyotype – Picture of the chromosomes found in an individual’s cells arranged in order of size & shape. With a karyotype it is easy to see if a certain chromosome is added, has a mutation or is missing all together.

15. Classwork! Summarize how bacterial cells divide by binary fission. What is the difference between a haploid and a diploid cell? What is the difference between a normal karyotype and one from a person whom has Down syndrome?