1. Unit 2 – Genetic Processes
Chapters 4, 5, 6

2. Cell Division & Genetic Material
Section 4.1
Cell Division & Genetic Material

3. Introduction to Genetics
Every living thing on earth is made up of cells
For new cells and new organisms to carry out their functions, its essential that they get the RIGHT genetic information
Genetics is the field of biology that involves the study of how genetic information is passes from 1 generation of cells to another

4. Review: Cell Theory All living things are composed of 1 or more cells
Cells are the smallest units of living organisms
New cells come only from pre-existing cells by cell division

5. Cell Theory
Since all new cells are the product of existing cells, then traits are passed from one (parent) cell, to the new cell (daughter)
When cells divide each new cell receives genetic information from the parent
The length of the cell cycle depends on the type of cell
i.e – fruit flies complete cycles in 8 mins vs. liver cells that take over 1 year to complete

6. The Cell Cycle
Cells reproduce through controlled growth and division in a process called the cell cycle
All somatic cells (cells that form the body of an organism) go through cell cycles

7. The Cell Cycle
Each time a cell goes through one complete cycle – it becomes two cells
In multicellular organisms, there are 3 functions of cell division:
Growth of the organism
Repair of tissues / organs that have been damaged
Maintenance to replace dying or dead cells

8. Stages of the Cell Cycle

9. Stages of the Cell Cycle
There are 3 main stages of the cell cycle
Interphase – a cell carries out its normal functions, grows, and makes copies of its genetic material in preparation for the next stage of the cycle
Mitosis – a cell’s nucleus and genetic material divide
Cytokinesis – begins near the end of mitosis and involves the division of the cell cytoplasm and creation of a new cell

10. Stages of the Cell Cycle : Interphase
Cells grow & develop into mature functioning cells
Copies its DNA
Prepares itself for division
This stage is divided into 3 phases
G1 / Grow 1 – major phase of cell growth
S / Synthesis – cellular DNA is copied (replicated) as it converts to chromatin fibres for the next phase
G2 / Growth 2 – cells synthesize more molecules prior to mitosis and cell division

11. Mitosis
Video:

12. Mitosis – Prophase
Here, the chromatin that was formed from DNA in the nucleus of a cell in interphase tightens into chromosomes in the longest phases of mitosis
1 pair of chromosomes are put together in the shape of an X
Each half of the X-shaped chromosome is called a sister chromatid (V- shape)
The two sister chromatids (˄ + ˅ = X) are held together at the centre by a centromere

13. Mitosis – Prophase
As prophase takes place, a bunch of small, hollow cylinders made of proteins called spindle fibres form at each end (pole) of the cell
They are used to help bring an even / orderly distribution of chromosomes to daughter cells during cell division
This ensure that each new cell created at the end has 1 complete copy of DNA

14. Mitosis – Prophase
Near the end of prophase, one end of each spindle fibre attaches to the sister chromatid of each chromosome on each side of the centromere
By this point, the nuclear membrane starts to break down

15. Mitosis – Metaphase
Here, sister chromatids line up in the middle of the cell along the equator
This makes sure that each new cell will have the right copies of chromosomes once it splits

16. Mitosis – Anaphase
Spindle fibres pull the centromere of each sister chromatid to opposite poles of the cell
This causes the sister chromatids to separate into 2 identical chromosomes at the same time

17. Mitosis – Telophase This is the final step of mitosis
Chromosomes get to the opposite sides of the cell
Chromosomes begin to relax and change back into chromatin (X →Ɩ ʃ ʅ)

18. Mitosis – Telophase
2 new nuclear membranes form around the chromosomes
The spindle fibres disappear
END ⇒ duplicated chromosomes have been divided and 2 new nuclei have formed

19. Cytokinesis This is the final step of the cell cycle in replication
Now, the cytoplasm is divided and the parent cell is separated into two complete cells
Once separated, the newly formed daughter cells enter interphase and carry out normal cell activities
These daughter cells have the same number of chromosomes as the parent cell (pair of 23 chromosomes = 46) this makes them known to be diploid cells

20. Differences in Cytokinesis
In Animal cells ⇒ do not have cell walls, so cell division of the cytoplasm begins at the cell membrane
Cells separate by pinching inward and cleave (divide) into 2 new cells
In Eukaryotes that HAVE cell walls (Plants, algae, fungi) ⇒
A cell plate (made up of material for the new cell membranes and new cell wall) forms in the middle of the cell that separates the new cells

21. Differences in Cytokinesis

22. Mitosis & Cytokinesis
Video:

23. Mitosis Online Activity
Complete the Key Concepts I: Mitosis Online Activity

24. Structure of Genetic Material

25. Structure of Genetic Material
DNA is made up of 2 long strands that form a spiral shape called a double helix
During the cell cycle, DNA exists as strands of chromatin fibre
Once mitosis begins, the chromatin condenses into distinct chromosomes

26. Structure of Genetic Material
Individual units of each strand of DNA are called Nucleotides
Nucleotides are made up of a phosphate group, a sugar group, and a base
There are 4 different bases in DNA
Adenine (A)
Guanine (G)
Thymine (T)
Cytosine (C)
Where each Base pairs specifically:
A- T, C-G

27. The Genome
DNA is often called “encoded” genetic material because the information is stored based on what group of nucleotides are linked together, within a SEQUENCE of DNA
Based on how nucleotides are grouped together in the sequence, certain traits are found
Nucleotides that code for what traits you inherit (eye colour, height, foot size) are = GENES
For example, if a group of CUA CUA CUA CUA nucleotides are together, then the gene tells us that a person can have blue eyes
The entire nucleotide sequence for a cell / organism is known as its GENOME
The Human Genome consists of 3 billion base pairs that are found in our 46 chromosomes (23 from each parent) in each of our somatic cells

28. Understanding Chromosomes
The Number of individual chromosomes in every cell differs from 1 species to another
Humans have 46 chromosomes / 23 pairs of chromosomes, where for each pair 1 chromosome is from the mother and one chromosome is from the father
1 chromosome pair (1 / 22) are Sex Chromosomes that are used to determine the sex of an individual, where
X + X = Female and X+Y = Male
The remaining 22 = Autosomal chromosomes

29. Understanding Chromosomes
Homologous Chromosomes
Chromosomes are paired based on their size and position of centromeres
When a pair matches, based on their size and position of centromeres, they are called Homologous Chromosomes

30. Understanding Chromosomes
However, homologous pairs are NOT identical to each other
Homologous chromosomes carry genes for the same trait (hair colour) at the same location, but they carry different forms of the same gene = alleles
The different forms account for the differences in specific traits, like blonde hair vs. brown hair

31. Examining Chromosomes: Karyotype
A karyotype is a picture of a person's chromosomes
In order to get this picture, the chromosomes are isolated, stained, and examined under the microscope
Most often, this is done using the chromosomes in the white blood cells

32. Examining Chromosomes: Karyotype
A picture of the chromosomes is taken through the microscope
Then, the picture of the chromosomes is cut up and rearranged by the chromosome’s size
The chromosomes are lined up from largest to smallest
A trained cytogeneticist can look for missing or extra pieces of chromosome that help ID genetic disorders

33. Examining Chromosomes