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Leaving Cert Biology Revision: Genetics, DNA and Evolution

Genetics, DNA, and Evolution


When a species exhibits variation, it indicates that its members differ in some ways.

Variants that are acquired are not inherited. For example, inherited variations are learned during life and for instance, inherited by DNA.


This is how genes are passed from parents to their children.


An area of DNA known as a gene is responsible for the synthesis of a protein.

The sequence in which amino acids bind together is determined by a gene, which is a segment of DNA. A protein is created in this way. Many times, the proteins are enzymes. In human bodies, enzymes regulate processes.

Gene Expression

The specific process by which a gene's genetic code is processed and utilized by the cell to produce a protein is known as gene expression.

Even if you are born tall, you will not develop into a tall person if you do not receive the proper nutrition.

Features: genetics and surroundings


About 60% of these are protein and 40% are DNA. DNA is securely coiled up in the nucleus thanks to proteins known as histones.

Genes that are not used can be found in large portions of DNA. 97% of our DNA is no longer functional. We refer to it as garbage DNA.

We can create DNA profiles using this junk DNA to identify individuals.


Deoxyribonucleic acid resembles a ladder that is bent.

It has two sides, or strands.

Two substances, called bases, hold the strands together.

We refer to these bases as complementary bases.

Four bases are present. Adenine T Thymine C Cytosine A, T, C, G G. Guanine

The Genetic Code

Three billion letters make up the entire human DNA molecule. The other strand will be... if one strand has the sequence TAGCAT.

A gene is a genetic code, which is a collection of nucleotides.

When this code is expressed, a gene functions. This indicates that the code leaves the nucleus and enters the cytoplasm.

To isolate DNA from a plant tissue

To disintegrate the phospholipids in the cell membrane, we add dishwashing solutions.

To get the DNA to cluster together, we add salt.

Enzymes that could damage DNA are denatured by immersing them in 600°C water for 15 minutes. We use ice for five minutes to inhibit the breakdown of DNA.

Using a blender, we break down the cell membranes and liberate more DNA. Coffee paper has large pores, therefore we use it to filter the cells and save the filtrate.

To release the DNA and break down the histone proteins, we add an enzyme. To finally extract the DNA from the protein, we add ice-cold ethanol.

Replication of DNA

We know that the cell nucleus splits by PMAT from mitosis. The nucleus of a cell must split before it may divide. Histone proteins firmly bind the chromosomes together.

The chromosomes must be duplicated to create an additional pair for the new cell for a nucleus to divide.

During interphase, DNA is copied.


The portion of DNA that has the phosphate, sugar, and nitrogen base is called a nucleotide.

A Sugar and P are connected to each base (A, T, C, and G).

These join with other nucleotides to create the DNA ladder's strands.

A nucleotide is the section of DNA that contains the nitrogen base, sugar, and phosphate.

Each base (A, T, C, and G) is linked to sugar and P.

These combine with other nucleotides to form the strands of the DNA ladder.

Replication of DNA

Procedures for Replication

1. DNA uncoils.

2. The base pair bond is broken by an enzyme.

3. The nucleus receives DNA bases from the cytoplasm.

They adhere to the strands' exposed DNA bases.

4. Every new strand is a mixture of the old and the new.

Every strand is a replica of the DNA strand that originated.

5. Every DNA strand winds back around to resemble a double helix.

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