1. DNA & Chromosomes

Success Criteria

Your learning has been successful if you can do the following:

  1. I can explain the relationship between cells, chromosomes and DNA.

  2. I can describe chromosomes in terms of their number, location, type and structure.

  3. I can draw and describe a labelled diagram of a DNA molecule.


Learn these so you can communicate this concept well.

  1. Autosomal chromosomes: All pairs of chromosomes that are not sex chromosomes.

  2. Chromosomes: Rod-like structure formed from a tightly wound DNA molecule. These ensure DNA doesn't get tangled up.

  3. Complementary base pairing: Adenine always pairs with thymine; cytosine always pairs with guanine.

  4. DNA: Very long molecule that carries the genetic code of an organism.

  5. Fertilisation: When egg and sperm fuse to combine their genetic material to form a zygote.

  6. Genes: Section of DNA that codes for a particular protein.

  7. Genome: All of the DNA in a cell.

  8. Homologous chromosomes: Pairs of chromosomes that carry the same genes in the same place. One comes from mum, the other from dad.

  9. Karyotype: Diagram to show the complete set of chromosomes in a cell.

  10. Nucleotide: It is made of one phosphate, one sugar and one nitrogenous base.

  11. Nucleus: Part of the cell where DNA and chromosomes are located.

  12. Protein: Molecules coded for by genes, and are the building blocks of our cells.

  13. Sex chromosomes: Pair of chromosomes that determine the sex of an individual.

  14. Somatic cell: Normal body cell

Hei Mahi (Do Now)

Do Now in your OneNote/Notebook:

Analyse the picture below.
Write down full sentences of what you think it is showing.

Hei Mahi (Do Now)

Do Now in your OneNote/Notebook - Do not write the questions:

Exit Task

In your Learning Journal:

Re-write this interpreting question so it is asking about DNA:

What are the parts?

Then, write an answer for it.

Exit Task

In your Learning Journal:

Re-write this interpreting question so it is asking about Chromosomes:

Why do you think it is like that?

Then, write an answer for it.

Overview of the Genetic Material in Cells

Cells are the 'building blocks' of organisms. Each cell has a 'control centre' called the NUCLEUS. Each cell nucleus contains a fixed number of structures called CHROMOSOMES (human body cells have 46 chromosomes).

A chromosome is a rod-like structure formed from a tightly wound DNA molecule.

DNA is an extremely long molecule containing the genetic code. The cell's total DNA (GENOME) contains all the instructions needed to build an entire organism.

Chromosomes ensure that DNA does not get tangled up in the nucleus.

Each chromosome carries hundreds or thousands of GENES.

A gene is a specific section of a chromosome (a specific section of the DNA molecule) that codes for the production of a particular PROTEIN.

A difference in DNA sequence results in a difference in how genetic information is read and can reate a different appearance (phenotype).

Structure of DNA

DNA (deoxyribose nucleic acid) is a very long molecule that carries the genetic instructions an organism needs to carry out MRS C GREN.

A DNA molecule is made up of two linked strands, twisted into a double helix (like a twisted ladder).

The two strands are linked by attraction of particular base pairs. A always pairs with T, and C always pairs with G. This is called COMPLEMENTARY BASE PAIRING.

DNA is made up of three subunits:

  1. phosphate

  2. sugar

  3. nitrogenous base

These three things together are called a NUCLEOTIDE. DNA is made of millions of nucleotides joined together.


Homologous chromosomes

In a normal body cell (called a SOMATIC CELL), you have 2 copies of each chromosome. One has been inherited from mum (via the egg) and one inherited from the father (via the sperm) during FERTILISATION.

These pairs of chromosomes are called HOMOLOGOUS CHROMOSOMES. Homologous chromosomes carry the same genes, in the same place.

Autosomal and sex chromosomes

In many species, the sex of an individual is determined by a single pair of SEX CHROMOSOMES. For humans, it is the 23rd pair (X and Y).

All other chromosomes (that do not determine sex) are called AUTOSOMAL CHROMOSOMES.


The KARYOTYPE diagrams show the complete chromosome set in a body cell.

  • For example, in the picture below, 46 chromosomes in human body cells are sorted into 23 homologous pairs. 23 chromosomes inherited from the father, 23 inherited from the mother.

  • For example, 14 chromosomes in pea plant body cells sorted into 7 homologous pairs. 7 chromosomes inherited from parent 1, 7 chromosomes inherited from parent 2.

Each species has a fixed number of chromosomes in the body cells of all individuals. Humans have 23 pairs of chromosomes, so humans have 46 individual hromosomes in total.

Some human chromosome facts

Humans largest chromosome (#1) is 247,249,719 base pairs long.

Humans largest chromosome (#1) has around 8000 genes.

Humans smallest chromosome (#21) has around 300 genes.

The DNA from a single human cell placed end on end would be around 2m long. Each chromosome 1.7 – 8.5cm long.

Only around 1.5% of a humans DNA actually codes for a protein.

Humans have 223 genes in common with bacteria.

If all the DNA from ALL the cells in a human was placed end on end it would reach to the Sun and back 4 times.

Other chromosome facts

Cats have 38 chromosomes.

Beans have 22 chromosomes.

Butterflies have 380 chromosomes.

Carp (fish) have 104 chromosomes.

Kangaroo have 12 chromosomes.

Ants have 2 chromosomes.

Yeast has 32 chromosomes.

Slime Mold has 12 chromosomes.

Dogs have 78 chromosomes.

Tasks & Homework

Grass Level Reading (Ms. Skevington's)

S1.9 (1) DNA & Chromosomes

Grass Level Task - Colour in this DNA Molecule

Colour in this DNA Molecule.pdf

Sky Level Task - Build a DNA Molecule!

Build a DNA molecule.pdf

Sun Level Task - Worksheet on DNA and Chromosomes.

S1.9 (1) DNA & Chromosomes.pdf

sciPad Workbook

  • Page 179 - Cell and Chromosomes

  • Page 180 - My DNA Model

  • Page 181 - The Genetic Code

  • Page 182 - Nucleotides

Education Perfect HOMEWORK

Work through the Education Perfect task called "S1.9 Concept 7: Reproduction & Meiosis."

Grass Level Task - Wordwalls!