Glossary of Genetics terms

Question 1

Allele

Answer 1

Changes in the DNA sequence cause a different version of a gene, called an allele. Alleles are also often called variants.

Question 2

Amino Acid

Answer 2

Amino acids are organic compounds made of nitrogen, carbon, hydrogen and oxygen. They are the basic unit of proteins. The DNA sequence in a gene encodes a string of amino acids which will undergo modifications to become a protein

Question 3

Autosome

Answer 3

A chromosome that is not a sex chromosome. Each horse normally has 31 pairs of autosomes, with one of each pair inherited from each parent. When the term autosomal is used to describe the mode of action of an allele, it means the allele is not sex-linked.

Question 4

bp (base pair)

Answer 4

DNA is made up of a sugar phosphate backbone (string) and four nucleotides (bases) called adenine (A), guanine (G), cytosine (C), and thymine (T). DNA is double stranded so these bases are counted in pairs.

Question 5

Carrier

Answer 5

A carrier of a genetic disorder has one copy of a recessive allele. The allele is recessive, so the horse does not show any signs of the disorder, but ‘carries’ the allele and can pass it on to their offspring.

Question 6

Chimera

Answer 6

When two fertilised eggs fuse to create a single animal, that animal will have one set of cells with one set of DNA mixed in with other cells that contain a different set of DNA. Chimerism is extremely rare

Question 7

Chromosome

Answer 7

DNA is arranged in long strings called chromosomes. Each horse normally has 31 pairs of autosomes and two sex chromosomes, either XX (in females) or XY (in males).

Question 8

Co-dominance

Answer 8

Because most genes occur on autosomes, each horse has two copies (alleles) of most genes. If the different alleles of a gene are co-dominant, it means that both exert their full effect on the animal. An example of co-dominance is in people of the AB blood type. They have alleles for both the A and B blood type and both are expressed.

Question 9

Complex trait

Answer 9

A trait that is influenced by both genetic and non-genetic (environmental) effects.

Question 10

DNA

Answer 10

Deoxyribonucleic acid (DNA) is a molecule that contains hereditary material that is passed down generations. DNA is made up of a sugar phosphate backbone (string) and four nucleotides (bases) called adenine (A), guanine (G), cytosine (C), and thymine (T). DNA is double stranded.

Question 11

DNA sequence

Answer 11

The order of nucleotides on a DNA strand.

Question 12

Dominance

Answer 12

Because most genes occur on autosomes or the X chromosome, each horse has two copies (alleles) of each gene. Dominance is when one allele masks the effect of the second.

Question 13

Embryonic lethal

Answer 13

A genotype that stops the embryo from developing is called embryonic lethal.

Question 14

Epigenome

Answer 14

All the modifications to the DNA that regulates the activity (expression) of all genes.

Question 15

Exon

Answer 15

A gene is a DNA sequence that contains the instructions to create a protein. Often the instructions are not continuous, so genes are made up of coding regions called exons interspersed with non-coding regions (introns).

Question 16

Gene

Answer 16

A sequence of DNA that contains the instructions to create a protein

Question 17

Gene expression

Answer 17

When a gene is turned on to make a protein. First the gene sequence is transcribed into RNA, then translated into a string of amino acids which are modified to create the protein.

Question 18

Genetics

Answer 18

Genetics is the study of heredity, the process by which parents pass information onto their offspring. Genetics is also the study of the characteristics of particular genes.

Question 19

Genome

Answer 19

All of the genetic material in an organism.

Question 20

Genomics

Answer 20

The study of all of the genetic material in an organism, often in more than one individual.

Question 21

Genotype

Answer 21

A description of the specific gene variants carried by in an animal.

Question 22

GWA

Answer 22

Genome wide association analysis. A scan of the whole genome to identify regions associated to a particular trait.

Question 23

Haplotype

Answer 23

A combination of alleles that are inherited together, usually because they sit close to each other on a chromosome.

Question 24

Heredity

Answer 24

The reason for the similarity between parents and their offspring. The transmission of characteristics down generations.

Question 25

Heterozygous

Answer 25

Having two different alleles at a particular locus or place on the genome.

Question 26

Homozygous

Answer 26

Having the same alleles at a particular locus or place on the genome.

Question 27

Incomplete dominance

Answer 27

Incomplete dominance is when an allele has a different effect when there are different numbers of the allele. It only has a partial effect if there is one copy compared to two. Cream dilution is an example of incomplete dominance.

Question 28

Incomplete penetrance

Answer 28

If an allele has incomplete penetrance, not every animal with that allele will express its full effects. Some animals with the allele may never show signs of that trait. An example is the disorder MYHM.

Question 29

Intron

Answer 29

A gene is a DNA sequence that contains the instructions to create a protein. Often the instructions are not continuous, so genes are made up of coding regions (exons) interspersed with regions called introns that do not code for protein.

Question 30

Locus

Answer 30

The location of a particular marker or gene on a chromosome.

Question 31

Marker

Answer 31

A DNA sequence (like a gene) or variant which has a known location.

Question 32

Mode of Inheritance

Answer 32

The way a trait is inherited and its action; eg autosomal recessive.

Question 33

Modifier

Answer 33

A gene that modifies the action or product of another gene.

Question 34

Mutation

Answer 34

A variation in the nucleotide sequence of DNA compared to the wild type (reference) sequence. The term mutation is often associated with a disease variant.

Question 35

Nucleotide

Answer 35

There are four types of nucleotides (bases) called adenine (A), guanine (G), cytosine (C), and thymine (T) that make up part of the DNA strand. The arrangement of these nucleotides in order is called the DNA sequence.

Question 36

Phenotype

Answer 36

The appearance of the animal, what is observed. This includes behaviour and physiology as well as physical appearance.

Question 37

Pleiotropy

Answer 37

When a single gene affects multiple phenotypic characteristics. An example is some Splashed White mutations which can affect both coat colour and hearing.

Question 38

Promotor

Answer 38

Sequence at the beginning of a gene that contains motifs to which proteins bind to and turn on translation of the gene into RNA.

Question 39

Polymorphism

Answer 39

A variation in the nucleotide sequence of DNA compared to the wild type (reference) sequence. The term polymorphism is often associated with a benign variant that doesn’t cause disease.

Question 40

Recessive

Answer 40

One of the modes of action of an allele. A recessive trait needs two copies of the recessive allele to produce (express) the phenotype. For example, the chestnut coat colour is recessive to bay.

Question 41

RNA

Answer 41

Ribonucleic acid (RNA) is similar to DNA but is a single stranded molecule. RNA contains uracil (U) instead of thymine (T). When a gene is switched on, the DNA in the gene is transcribed into a string of RNA, then RNA is translated into a string of amino acids before being processed into a completed protein.

Question 42

Transcription

Answer 42

The creation of RNA from DNA.

Question 43

Translation

Answer 43

The creation of a protein from an RNA strand. First the RNA is translated into a string of amino acids, then this is processed and packaged into a mature protein.

Question 44

WGS

Answer 44

Whole genome sequence. The whole genome sequence of a horse is approximately 2.7 billion base pairs long.

Question 45

Wild-type

Answer 45

The wild type version of a gene is the original version that existed before a mutation occurred. It is the ancestral version.