What is genetics?

Genetics is the study of hereditary elements of any living organism.


What is hereditary elements?

Hereditary elements are DNA. All living things have DNA - birds, humans, animals, trees, fish, plants, bacteria and even viruses. DNA basically looks the same in all of these organisms. Hereditary means it is passed on from parents to offspring. Each and every cell of a body (thus hair, skin, heart, brain, bone etc) all have exactly the DNA molecule. But the DNA molecule differ slightly between individuals of the same species and differ a lot between species.


What does DNA look like?

To get a picture of DNA in your head, the easiest is to imagine a spiral staircase. The DNA molecule is a double helix molecule so it looks like a spiral staircase with handlebars on both sides. The handlebars are there to support the structure and doesn't have a role in passing along traits. The important part of the molecule is the "stairs". In genetics we call these nucleotides or bases. There are four different bases found in DNA - Adenine (A), Cytosine (C), Thymine (T) and Guanine (G) or for short only A, T, C and G. A and T always bind and C and G always bind.


Figure 1: A representation of how the nucleotides bind to form base pairs

Each stair of the staircase actually consist out of 2 bases or a base pair, either A-T or C-G. This long molecule is then twisted in a spiral to give it the double helix shape.


What are chromosomes?

DNA is packed tightly into each cell. The suitcase in which DNA is packed is called chromosomes. Each species has a unique number of chromosomes and we are unsure why a species has that number of chromosomes as it is not linked to intelligence or to a number of genes. For example humans have 46 chromosomes. These chromosomes are paired so in effect we only have 23 pairs. Of these 22 pairs are autosomal or "body" chromosomes and one pair is the sex chromosomes. In birds we find macro - and micro-chromosomes as well and it seems that the micro-chromosomes contain more genes.


What are genes?

DNA is basically the arrangement of 4 bases or 2 base pairs in different combination. The combination or SEQUENCE of the bases are what is important for us. Imagine the DNA string as a road leading through a small town and each of the shops and houses as a base pair. In the town you will find different shops and the SEQUENCE of the shops is known to the people in the town. In order for the town to function properly this sequence of shops need to stay the same. If the butcher and the baker suddenly swap places, then there will be chaos in the town. The same happens in a gene. A gene is simply a part of the DNA where the bases are in a specific order and it has a function. Genes differ in length.


What are mutations?

Mutations are changes in the base pair sequence of a gene. Like in the previous example where the butcher and baker swapped places we had chaos in the town. A mutation can have a good e.g. a new plumage color variation or bad e.g. a genetic disease, effect. And mutations can only occur in a gene. Mutations are caused by one of three effects:

  1. Substitution - if one nucleotide is substituted by another nucleotide e.g. there is an A at a position of all healthy birds but there is a C at birds with a specific disease
  2. Deletion - one or more nucleotides are deleted from the gene
  3. Insertion - one or more nucleotides are inserted in a gene

What is the genome?

The genome is the combination of all the DNA of an organism. So we could say the genome is the library of all of the DNA of an organism.


"Junk" DNA

Genes only make up a small portion of any organism's DNA. The rest is called "junk" DNA. In the human genome, it is estimated that 98% of all our DNA is "junk". However, scientists are only starting to discover which hidden treasures lies buried in all the junk. In the field of animal breeding, and especially cattle breeding, the power of markers linked to certain genes is being used to select animals for breeding. These markers, called Single Nucleotide Polymorphisms or SNPs, are single bases that have different nucleotides at that specific position. For example, half the population of cattle will have an A at a position and the other half a T. There are millions of SNPs throughout the genome and not all of them are linked to a gene. These SNPs are linked to genes which mean that if an animal has a specific combination of SNPs it may produce more milk or better quality meat.


More on SNPs

In the last couple of years SNPs have been proven to be very useful in different fields of genetics and very much so in animal breeding. SNPs can be considered as a mutation - one nucleotide is substituted for another - and if the SNP is in, or linked to a gene there will be an effect but if it is outside of a gene there will not be any effect.

SNPs are also used when we need to confirm if an individual is the parent or family member of another. In this study we will be identifying SNPs that can be used to identify parents of a bird.