1. Key Area : 2 DNA, genes and chromosomes Unit 1: Cell Biology

2. Chromosomes The nucleus of the cell is very important as it controls all the activities of the cell. Chromosomes are found in the nucleus of cells and it is these biological units that are key to deciding what activities the cell will be involved in. In the nucleus of the cell, the chromosomes look like thread like structures. When a cell starts to undergo cell division, however, they become more visible. National 4 Biology Cell Biology

3. Chromosomes Each normal body cell has two matching sets of chromosomes. The 46 chromosomes normally found in a normal human cell is made up of two matching sets of 23 and they can be arranged in order as shown in the karyotype diagram. The only difference between the two sexes is that a human female has two X chromosomes, XX, while a human male has an X and a Y chromosome, XY. These are called the sex chromosomes. National 4 Biology Cell Biology

4. Human karyotype National 4 Biology Cell Biology

5. Chromosomes Chromosomes are made up of DNA. DNA stands for DeoxyRiboNucleic Acid. DNA is a very long molecule as it contains many, many instructions that make up living things. It contains a code that gives living things the instructions they need to make protein. Inside the nucleus the DNA is wound up very tightly into the chromosomes in order to fit it into the tiny cell. It is wrapped up and tightly organised so it doesn’t get tangled or muddled in the nucleus National 4 Biology Cell Biology

6. Chromosomes National 4 Biology Cell Biology If you took the DNA from all the cells in your body and lined it up end to end, end to end, it would form a strand 6000 million miles long (but very, very thin).

7. Chromosomes DNA consists of two molecules or strands that form a double helix. The strands are held together by weak bonds that form between pairs of bases. There are 4 base pairs in DNA. They are adenine (A), guanine (G), thymine (T) and cytosine (C). These base pairs only bond together cross the DNA strands as: Adenine - Thymine or A-T Cytosine – Guanine or C-G. National 4 Biology Cell Biology

8. Genes National 4 Biology Cell Biology A gene is a short section of DNA. Each short section of DNA contains a specific order of the 4 bases that are available (A-T, C-G). These bases code for specific amino acids which are the building blocks of all proteins. Proteins form the structure of our bodies, as well as playing an important role in the processes that keep us alive.

9. Genes National 4 Biology Cell Biology A gene is a length of protein that codes for a specific protein. For example, one gene will code for the protein insulin which plays an important role in helping your body control the amount of sugar in your blood. Genes are the basic unit of genetics. Human beings have 20000 to 25000 genes. These genes account for only about 3% of our DNA. The function of the remaining 97% is not clear, but it is thought they have something to do with controlling the genes.

10. Genes National 4 Biology Cell Biology Your genes are part of what makes you the person that you are. You are different from everyone alive now and everyone who has ever lived. Your DNA is unique to YOU Your genes also mean that you probably look a bit like other members of your family. Genes influence what we look like on the outside and how we work on the inside.

11. Heredity National 4 Biology Cell Biology Heredity is the passing of traits to offspring from its parents or ancestors.

12. Uses of DNA National 4 Biology Cell Biology Every individual has a DNA profile which is a distinctive pattern or set of numbers that represents a much larger DNA sequence. This profile is unique to the person it belongs to because everyone's DNA is unique to them. Identifying an individual’s DNA profile has proved to be one of the world’s most powerful forensic tools

13. Uses of DNA National 4 Biology Cell Biology DNA can be extracted from different people and compared using techniques known as genetic fingerprinting or DNA profiling. These techniques can be used in forensic science to solve crimes such as murder and rape. The same techniques are used in paternity testing.

14. Uses of DNA National 4 Biology Cell Biology DNA profiling can be used to link individuals to crimes and free those that are innocent. The process involved extracting DNA from bodily fluids, white blood cells and tissue samples. If DNA samples found at a crime scene match a suspect then it is more than likely that the suspect is guilty.