Deoxyribonucleic Acid

From DNA to you!

Ingredients:

• Deoxyribose (sugar)

• Phosphate group

• Nitrogen base

Location: nucleus of the cellOccupation: carries heredity information

Nitrogen bases

4 possible:

• Adenine always pairs with Thymine

• Cytosine always pairs with Guanine

A*T and C*G

Nucleotides combine & form long chains.

* Chains are joined by HYDROGEN bonds between the bases.

Let’s look at the structure of DNA…

All organisms contain DNA, made of nucleotides, with A-T-C and G…

SO HOW CAN ORGANISMS BE SO DIFFERENT?

* The order of the nucleotides in the DNA strands is different.

The sequence of nitrogen bases is a code for the making of proteins.

This is the GENETIC CODE - proteins are built from amino acids.

The code works in sets of 3.

3 nitrogen bases = 1 amino acid = codon

Before we can make a protein, we have to make RNA.

DNA is involved in 3 processes:

1. 2. 3.

The genetic code is universal.

This means the codons represent the same amino acid in all organisms!

There are 20 different amino acids.

Gregor Mendel

*The father of genetics

Mendel was the first to carry out studies of heredity.

Heredity --> passing on of characteristics from parent to offspring

Genetics - branch of biology that studies heredity.

Characteristics that are inherited are called traits.

Mendel predicted how traits are transferred from one generation to the next --> using pea plants.

He crossed plants with different traits.

Example: A tall plant X short plantGreen seeded plant X Yellow seeded

Genes are the basic unit of inheritance. -> located on our chromosomes.

• One gene is inherited from the female parent and one from the male.

How genes work…

If one trait is masked or covered up by the other, the trait that hides the other is dominant.

(capital letters: A, B, R, Y)

The trait that is covered up or hidden is recessive.

(lower case letters: a, b, r, y)

If both traits are dominant (CAPITAL), the organism is homozygous dominant.

If both traits are recessive (lower case), the organism is homozygous recessive.

These organisms are purebred.

Homozygous means “SAME”

If one trait is dominant and one is recessive, the organism is heterozygous. (capital & lower case)

These organisms are hybrids.

Heterozygous means “different”!

Heterozygous individuals are also called

carriers.--> They “carry” the recessive gene.

Genes exist in alternative forms.

--> These different gene forms are called alleles.

* Allele refers to the “letters.”

* Used to determine the probability (or ratio) of expected offspring

Genotype: organism’s gene combination

Phenotype: organism’s physical appearance, the way it looks