The Genome, Chromosomes, DNA and Genetics


Chromosomes, Genes and DNA 

In every cell we find genetic material (they are thread like structures called chromosomes) If we enlarge them, we would see they consist of a chemical called DNA (deoxyribonucleic acid.) Chromosones are didvided ito a number of functional sections called genes. Each gene controls a particular characteristic e.g eye colour. 


Your body is made up of cells

Each cell contains a nucleus which controls the cell

Each nucleus contains lots of thin threads called chromosomes (which carry info. which controls how your body works and what you look like)

There are 46 chromosones in a human cell (23 from your mum and 23 from your dad)

Each chromosome is made up of tangled threads. Each thread is made up of a very long molecule called DNA.

A gene is a length of DNA. Each gene gives instructions for a different characteristic e.g eye colour (there are 100's of genes in each chromosome) 

Chromosomes occur in functional pairs (with the exception of the sex cells) 


Chromosone: found in the nucleus- carry the information of your genetics 

Gene: Short length of DNA found on the chromosomes 

Genome: all the DNA in all of the genes in all of the chromosomes in a person 

DNA Structure 

The nucleotides are then joined together to form a double helix. It resembes a ladder with interlinking rungs that has been twisted. 

DNA consists of 3 smaller units which are repeated throughou the length of the whole molecule. Together these 2 units make a nucleotide. 

there are 4 types of bases:

1. adenie

2. thymine

3. cytosine

4. guanine 

Base pairing rules:

cytosine = guanine (c + g)

Adenine = thymine (a + t)

learn double helix diagram on page 8

How does DNA work? 

- not done yet (page 8 of bookelt)

Cell Division 

How do organisms grow?

by increasing the number of cells 

Cells can double by splitting in half. When cells divide during growth they will make 2 new cells, called daughter cells (each with exactly the same genetic information as each other and as the parent cell) Ultimately they are genetically identical clones

Therefore every celll in the growing organism has the same number and type of genes and chromosomes and that these are the same as they were in the very 1st cell, the zygote. 

This type of division is called Mitosis


Mitosis is used for growth, to replace worn out cells and to repair damaged tissue 

What is Mitosis? 

the exact duplication of chromosones, producing 2 daughter cells that are genetically idential to the parent cell. 

look at diagram on page 10


 -> responsible for the production of gametes (egg and sperm cells). It can be described as a reduction divsion as the cells produced contain 1/2 the original  number of chromosomes. During meiosis the cell undergoes 2 divsions producing 4 daughter cells. 

-> Most humans have 46 chromosomes (arranged in 23 pairs).


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