1. Chromosomes and Cell Reproduction
Chapter 6 and Section 9.1 in Green Book
Chromosomes and Cell Reproduction

2. Essential Vocabulary Text Book: Green Book: Somatic cells Cell cycle
Gamete
Autosome
Binary fission
Sex chromosome
Gene
Chromosome
Karyotype
Chromatid
Cell cycle
Centromere
Interphase
Homologous chromosome
Mitosis
Cytokinesis
Diploid
Cancer
Haploid
spindle
Zygote
Green Book:
Somatic cells
Cell cycle
Interphase
Mitosis
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Replicate
Centromere
chromatin

3. Chromosomes Section 6.1 Key Concepts
Cell division allows organisms to reproduce asexually, grow, replace worn-out or damaged tissues, and form gametes.
Bacteria reproduce by binary fission.
Before cell division, DNA coils tightly around proteins and forms chromosomes. At cell division, each chromosome consists of two chromatids attached at the centromere.
Each organism has a characteristic number of chromosomes.
Human somatic cells are diploid, with 23 pairs of homologous chromosomes. Human gametes are haploid with 23 chromosomes.
Sex chromosomes carry information that determines an organism’s sex.
Changes in chromosome number or structure can cause abnormal development. Karyotypes are used to examine an individual’s chromosomes.

4. Objectives
Identify four examples of cell division in eukaryotes and one example in prokaryotes
Differentiate between a gene, DNA molecule, chromosome, and chromatid
Compare haploid and diploid cells
Predict how changes in chromosome number or structure can affect development

5. How Cells are Formed by Cell Division
Regardless of the type of division, DNA must be present in the resulting cells.
When a cell divides, the DNA is first copied and then distributed so that each cell ends up with a complete set of the DNA.
About 2 trillion cells are produced by an adult human body every day!
Cell division occurs in humans and other organisms at different times in their life.
Bacterial cells undergo reproduction by dividing
Eukaryotic cells undergoing growth, development, repair, or sexual reproduction divide by a different type of cell division.
The formation of reproductive cells, called gametes, is yet a third type.

6. Bacterial cells divide to reproduce
Bacterium’s single DNA molecule is circular and is attached to the inner cell membrane.
Bacteria reproduce by a type of cell division called binary fission.
Binary fission is a form of asexual reproduction that produces identical offspring.

7. Binary Fission Occurs in 2 stages DNA is copied The cell divides
Divides by adding a new cell membrane to the point on the membrane between the two DNA copies
New cell wall forms around the new membrane
Eventually pinched into 2 independent but identical cells

8. Eukaryotic cells form chromosomes before cell division
Vast amount of information encoded in DNA is organized into units call genes
A gene is a segment of DNA that codes for a protein or RNA molecule
Linked like a train
Genes play an important role in how a person develops and functions
DNA is stretched out so information can be used to direct protein synthesis

9. Chromosomes: coiling and division
As a eukaryotic cell prepares to divide, the DNA and the proteins associated with the DNA coil into a structure called a chromosome.
Before it coils, DNA is copied
Two exact copies make up a chromatid and attached at centromere
Centromere is the point of separation during cell division

10. Chromosome Number and Structure Affect Development
Each human somatic cell (any cell that isn’t a gamete) normally has 23 pairs of chromosomes
They differ in size, shape, and set of genes
Each chromosome contains thousands of genes that play important roles in determining how a person’s body develops and functions.
For this reason, possession of all chromosomes is essential to survival.

11. Sets of chromosomes
Homologous chromosomes are chromosomes that are similar in size, shape, and genetic content
Each one in a set comes from one parent
1 from mom, from dad

12. Sets of chromosomes Diploid- contains two sets of chromosomes
Somatic cells 2n
Haploid- contains one set of chromosomes
Gametes n
Zygote- fertilized egg cell, first cell of new individual

13. Each organism has a characteristic number of chromosomes

14. Chromosomes determine your sex
Autosomes are chromosomes that are not directly involved in determining gender
Sex chromosomes determine gender

15. Change in chromosome number

16. Change in chromosome structure
Changes in an organism’s chromosome structure are called mutations
Deletion- a piece of chromosome breaks off completely
Duplication- chromosome fragment attaches to its homolog
Inversion- chromosome piece reattaches to the original chromosome backwards
Translocation- piece reattaches to a nonhomologous chromosome

17. Section 6.1 Review
Summarize how bacterial cells divide by binary fission.
Identify the point in a eukaryotic cell’s life at which DNA coils up to form chromosomes.
Summarize the difference between a haploid cell and a diploid cell.
Compare the sex chromosomes of human females with those of human males.
Compare the karyotype of an individual with Down syndrome with a normal karyotype.
A student concludes that homologous chromosomes are found in gametes. Do you agree or disagree?

18. The Cell Cycle Key Concepts
Section 6.2
Key Concepts
The life of a eukaryotic cell—the cell cycle– includes interphase, mitosis, and cytokinesis.
Interphase consists of 3 phases: growth, DNA synthesis (replication), and preparation for cell division. A cell about to divide enters the mitosis and cytokinesis phases of the cell life cycle.
The cell cycle is carefully controlled; failure of cellular control can result in cancer.

19. Objectives
Identify the major events that characterize each of the five phases of the cell cycle
Describe how the cell cycle is controlled in eukaryotic cells
Relate the role of the cell cycle to the onset of cancer

20. The Cell Cycle Describes the Life of a Eukaryotic Cell
The life of a eukaryotic cell is traditionally shown as a cycle
The cell cycle is a repeating sequence of cellular growth and division during the life of an organism
A cell spends 90% in interphase, the first phase
Only moves forward to the next phases when it is about to divide
Cell division in eukaryotic cells is more complex than cell division in bacteria
Organelles have to be rearranged before the cell can properly divide and form 2 fully functioning cells

21. The cell cycle
First Growth (G1) phase- the cell grows rapidly and carries out routine functions
Synthesis (S) phase- DNA is replicated, two chromatids attached at centromere
Second Growth (G2) phase- preparations are made for nucleus to divide, microtubules are assembled
Mitosis- the process of cell division in which the nucleus of the cell is divided into two nuclei
Cytokinesis-the process during cell division in which the cytoplasm is divided

22. The cell cycle

23. The Cell Cycle is Carefully Controlled
If a cell spends 90% of its time in interphase, how do cells know when to divide?
How is the cell cycle controlled?
Like traffic lights, cells have a set of “red light—green light” switches that are regulated by feedback information from the cell.
The cell cycle in eukaryotes is controlled by many proteins.
Control occurs in three principal checkpoints.

24. Checkpoints
Cell Growth (G1) Checkpoint-makes the key division if the cell will divide. Cell must be healthy and large enough. Cell will hit a yellow light if it needs a resting period
DNA Synthesis (G2) Checkpoint- DNA replication is checked at this point by DNA repair enzymes
Mitosis Checkpoint- triggers the exit from mitosis, signals beginning of G1 phase

25. Section 6.2 Review
Differentiate between the G1, G2, and S phases of the eukaryotic cell cycle.
Relate the onset of cancer to three major check-points at which the cell cycle is controlled.
Identify the type of environmental factors that can cause mutations that may lead to cancer.
Why are individual chromosomes more difficult to see during interphase than during mitosis?