1. GENETICS The Science of heredity
In the 19th century Gregor Mendel, an Austrian monk, discovered that living things inherit their physical feature due to discrete genetic traits that we now call GENES.
We know that these traits are made of DNA.

2. What is DNA?
DNA (deoxyribonucleic acid) is a molecule that contains all the instructions and information to:
Help and organism live and grow.
Allow cells to know what role they play in the body.
DNA is found in the nucleus of eukaryotic cells as well as in bacterial cells.
What is DNA? ?

3. A always pairs with T C always pairs with G
DNA can contain information due to it’s structure.
DNA is a long molecule made
in the form of a double helix
(twisted ladder)
The “rungs” are built with 4 DNA “letters” or bases A, C, T & G.
A always pairs with T
C always pairs with G
A -> adenine T -> thymine
C -> cytosine G -> guanine
What is DNA? ?

4. What is a Gene?
Genes (“ DNA words”) are parts of the DNA molecule made of groups base pairs triplets (“3 DNA letters = 1 word or gene)
Each gene instructs the body to make 1 protein
These proteins include enzymes, structural proteins, hormones etc. Together these proteins allow an organism to live, grow and have specific characteristics.

5. What is a Chromosome ?
If the DNA in one cell were stretched out into one line it would be 3 meter long.
To fit into the cell the DNA is packaged into compact units called chromosomes.
To fit all of the DNA into chromosomes the DNA is first twisted into a double helix then further twisted around protein molecules.
Humans have 23 pairs of chromosomes giving a total of 46. (see cell size & scale)

6. Organisms that reproduce sexually get half of their genetic material from the female parent and half from the male parent.
In humans the genetic material from one chromosome in each pair comes from the mother and genetic material from the other chromosome in the pair comes from the father.
The sex chromosomes are both the same in a female (XX) but different in a male (XY).
Only a male parent can pass on a Y chromosome therefore it is the male parent who determines the gender of the child.

7. What is Heredity?
Heredity involves the passing down of “traits” from parents to their children
Our genes encode instructions that define our traits.
The environment can also affect our traits (ex hair gets lighter in the sunlight).
Humans have two complete sets of 23 chromosomes (2 x 23=46)
To pass down genetic traits to an offspring -> each parent gives 1 set (23) of chromosomes to their child

8. What is a trait? A trait is a notable feature or quality in a person.
We inherit a unique combination of traits from our parents.
We pass a different combination of traits to our children.
Traits can be:
Physical (ex eye colour or height).
Behavioural (ex a dogs instinct to fetch)
Medical -> these give a predisposition to a disease or condition such a diabetes or sickle cell anemia

9. HOW WE INHERIT TRAITS
For each trait we have 2 alleles (one from each parent).
Some alleles have the code for a dominant trait (the trait is seen) other alleles are recessive (the trait can be hidden).
For each trait we might have:
2 dominant alleles or 2 recessive alleles (Homozygous -> both alleles are the same)
1 dominant & 1recessive allele
(Heterozygous -> both alleles are different)