Understanding the work of the Sheep CRC can sometimes be difficult and raises many questions. Therefore, we have created this page of FAQs to help you build a foundation of understanding.
If you have a question about any of the terms below, please send your query to:
Rhonda Brooks, Sheep CRC Communications Officer via fax to 02 6773 1400 or via email to firstname.lastname@example.org
What is genetics?
Genetics is the science of heredity and variation in living organisms.
What is genomics?
Genomics is the study of the genomes , ie. the full set of genes or chromosomes, of organisms.
What is a gene?
A gene is the most basic unit of heredity. It consists of a relatively short sequence (several thousand nucleotides) of DNA at a specific location on a chromosome that determines a particular characteristic in an organism through the production of a specific protein end-product. For further information click here.
What is heredity and how does it work?
Heredity is the passing of traits to offspring (from its parent or ancestors). This is the process by which an offspring acquires the characteristics of its parents.For further information click here.
What is a phenotype?
A phenotype is any observable characteristic or trait of an organism: such as its morphology, development, biochemical or physiological properties, or behavior. Phenotypes result from the expression of an organism's genes as well as the influence of environmental factors and possible interactions between the two.For further information click here.
What is a genotype?
The genotype of an organism is the inherited instructions it carries within its genetic code.
What is DNA?
DNA, or deoxyribonucleic acid, is the building block of the genetic code. A DNA molecule is composed of two strands of nucleotides wrapped around one another and connected at the bases to form a double helix. DNA is present in all nucleated cells in an animal, with cattle having approximately 2.7 billion nucleotides in the code. DNA is organized into 30 pairs of
chromosomes in cattle. We refer to the complete DNA makeup of an animal as its genome.
For further information on DNA click here.
What is a DNA marker?
A DNA marker is a variation in the DNA code, mapped to a specific location in the genome. DNA markers can be genotyped and may be associated with one or more physical characteristics.
Are all DNA markers alike?
Markers can differ in mode of inheritance, physical size (number of base pairs), functionality and how they are applied in genetic improvement. The prevailing type of marker now being used in DNA testing for traits is known as a single nucleotide polymorphism (SNP). SNP markers vary at a single base location in the genome, creating two different alleles (or forms) of the marker.
For further information on SNPs click here.
How does a DNA marker relate to a gene?
A DNA marker can actually be located directly within the gene sequence that causes a change in the trait of interest. More commonly, DNA markers are linked to (inherited with) a nearby gene that causes a change in the trait of interest.
Do we know the full code (i.e., sequence) of DNA for cattle and other livestock?
The full code set for an animal’s genome is comprised of about 2.7 billion connected bases. The genome of a number of species has been sequenced including humans, cattle, chickens, horses, and the platypus! Additional commercially important species such as sheep and swine are currently being sequenced.
How is an animal’s makeup (i.e., genotype) for a DNA marker determined?
An individual’s genotype is fixed at birth with the inheritance of one chromosomal copy from each of its parents. The animal’s genotype for the marker is determined by analyzing the DNA sequence variation at the marker location in the genome using high throughput DNA genotyping technologies that are routinely used around the world for a variety of applications.
Will an animal’s marker genotype change during its lifetime?
No, an individual’s genotype is unique and fixed not long after fertilization of an egg by a sperm, and remains fixed throughout its lifetime.
Does a DNA marker only relate to one trait?
Many traits are genetically correlated to one another due to the fact that genes can impact multiple traits. Likewise, DNA markers that are either within these genes or linked to them are likely to have effects on multiple traits. It is also possible for a marker to have a positive effect for one trait and a negative effect for another.
What is an economically relevant trait?
A trait is an observable or measurable characteristic of an individual. An economically relevant trait is one that directly affects profitability through an association with a specific cost of production or income stream. Examples of economically relevant traits include reproduction, lean meat yield and feed efficiency.
Are all economically relevant traits heritable?
Economically relevant traits vary in level of heritability, measured as the percentage of observed variation that is due to underlying gene effects that can be transmitted from one generation to another. While heritability may differ between populations, in general, traits such as fertility tend to be more lowly heritable than traits such as growth rate and tenderness, which exhibit moderate to high degrees of heritability.
If a trait is lowly heritable, does that mean that it cannot be improved genetically?
Traits with a low degree of heritability can still be improved genetically, though not as rapidly as more highly heritable traits. The rate of genetic progress is not controlled by heritability alone; the amount of observable (phenotypic) variation and the accuracy with which the variation can be identified are also key factors.
How many genes are responsible for the expression of economically relevant traits?
We do not yet know exactly how many genes impact economically relevant traits, but research indicates that many genes are likely to have small- to moderate-sized effects on performance for any given trait.
Are the effects of DNA markers the same for different breed sub-populations around the world?
Often they are similar, although the more divergent or distant a population is from another, the greater chance there is for the effect of markers to vary.
Answers to these questions have been prepared with the help of the Beef CRC.