Why did your parents have you? …I mean you, a human child. Why not a hippo, or cactus, or a gorilla?

They had no choice! It’s coded in the DNA of every cell of their body, and it’s in every cell of your body!

DNA The molecule of life!

Within the nucleus of each cell lies a number of chromosomes. In humans, and many animals, chromosomes come in pairs. Humans have 23 chromosome pairs. Predict: Why do you think human chromosomes are paired?

Chromosomes are composed of tightly wound strands of a molecule called DNA (Deoxyribonucleic acid). DNA’s double helix looks like a twisted ladder. Each cell contains over 1m of DNA! This is 1 000 000 times longer than the cell it came from! In total, you have about 9 million kilometres of DNA. That's enough to reach to the moon and back 13 times!

Think: Why is DNA so long?

Think of all the traits you posess… height eye colour hair colour tongue roller handspan freckles hairline thumb skin pigmentation blood type dimples nose width earlobe body size handedness

But where could all of that information be stored? If you came from an embryo which came from a zygote which came from a cell, then all the information that makes you you must have been somehow within that one cell!

This train of thought raises an interesting question… How did I go from one cell with one set of DNA to two cells with two sets of DNA?

DNA is “written” in an alphabet of chemicals called bases. The secret lies in the chemistry of the DNA itself. There are four unique base pairs that that are responsible for the language of life found in all living things!

The four bases are guanine, cytosine, adenine, and thiamine represented by the letters G, C, A, and T, respectively.

DNA Replication Demo

A list of the bases of the entire DNA in your genes, (A, C, T, G) would fill over 200 phone books. That’s 3 billion letters!

hair colour tongue roller freckles thumb blood type nose width Each of your inheritable characteristics is encoded on part of the DNA strand in a sequence of base pairs called a gene. body size

eye colour gene brown allele Offspring of sexual reproducers inherit 1 of each chromosome from each parent. This means they also have 2 copies of each gene. Example: A son inherits the gene for brown eyes from his father, and blue eyes from his mother… An allele is a possible form of a gene. eye colour gene blue allele

What other alleles can you think of?

Think about it… Is only one allele active? both?