Chapter 6 Chromosomes Cell Reproduction 6 1 Chromosomes

Chapter 6 Chromosomes & Cell Reproduction 6. 1 Chromosomes

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

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.

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)

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.

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

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.

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

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.

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 = 1 n Diploid = 2 n n = a variable, for instance in humans n = 23

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. • 1 n + 1 n = total chromosome number • Eg. 23 + 23 = 46 chromosomes • Females send an X chromosome & males send either an X or a Y

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?

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.

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?