Term Definition
Accuracy
The accuracy of an EPD is a measure of how true the EPD is to the animal's actual (but unknown) genetic value. Accuracy values range from 0 to 1 with 0 meaning the EPD is not close to the animal's true breeding value and 1 meaning the EPD is exactly the animal's true breeding value. The accuracy is based on the amount and the type of data used to generate the EPDs. With more information on an animal and more information from progeny as opposed to distant relatives, the accuracy will improve.
Additive value
Additive value in genetics refers to breeding value for traits that are controlled by multiple genes (polygenic), each gene adding or reducing to the genetic potential for that trait for that animal. An example of this is growth, where several genes are involved in an animal's genetic ability to grow faster and the combination of these genes will represent the animal's growth. These are important to animal breeders as these are the genetic component that we select for with EPDs.
Affected
An animal has two recessive alleles of a gene and typically displays the recessive phenotype. This can only happen if both parents carry at least one copy of the recessive allele. If mated, affected animals will always pass the recessive allele on to their offspring.
Allele
Genes have variations called alleles. For instance, one gene that controls coat color is called the extension gene. This gene has three variations or alleles which are black (E), red (e), or wild type (Black-brown color, E+).
Carrier
An animal that is heterozygous for a certain gene, usually with one copy of the dominant allele and one of the recessive; typically in reference to a genetic condition. In simple recessive defects like AM, an animal that is a carrier would have one normal copy of the allele and one defective copy. This animal would not display the defect, but would pass the defective allele to half of its progeny.
Chromosome
A linear structure in the nucleus of the cell that contains genetic material (DNA). Chromosomes are inherited in pairs, one from each parent. Two sex chromosomes, X and Y, determine the sex of an animal. An XX animal will be female and an XY animal is male. Cattle have 30 pairs of chromosomes (n = 60 total), 29 paired autosomal chromosomes and two sex chromosomes. Humans have 23 pairs of chromosomes (n = 46 total, 22 paired plus two sex chromosomes).
Complementarity
In reference to crossbreeding programs, complementarity refers the combination of traits from separate breeds that complement one another so that the hybrid offspring have the optimum combination of traits. For instance, crossing Angus with Simmental results in SimAngusTM offspring that produce an ideal beef product with the high marbling characteristics from the Angus genetics and improved yield grades from the Simmental genetics.
Crossbreeding
Mating parents of two different breeds. Crossbreeding allows producers to take advantage of complementarity and heterosis. In other words, they can tailor their breeding program for the ideal cross of two breeds (complementarity) and gain a burst of production (due to heterosis).
Direct EPD
The EPD measuring the individual's own genetic merit for that particular trait. For example, calving ease direct would estimate the percent unassisted births for heifers bred to that bull.
DNA (Deoxyribonucleic acid)
DNA provides the code for inheritance from our parents. DNA is strung in a linear form in chromosomes and contains 4 distinct units (nucleotides or base pairs). The base pairs are adenine (A), guanine (G), cytosine (C), and thymine (T). The linear sequence of the base pairs provides the code for genes and ultimately proteins. The DNA sequence is translated into mRNA sequence. Three bases of mRNA code for a specific amino acid which is the building block for proteins. The DNA sequence determines mRNA sequence which determines the amino acid sequence in proteins which are ultimately the workhorse of the cell. DNA is replicated every time a cell divides and for the most part, every cell in your body has the exact same DNA sequence in the nucleus. Should an error occur in the DNA sequence during replication, this error will be repeated in subsequent cell replications. The mutation is only passed onto the next generation when errors occur in a sperm cell or an oocyte (egg).
Dominant trait
A dominant trait means an animal needs only one copy of the allele to display the trait. An example of a dominant trait would be black coat color. If an animal gets one copy of the black allele and one copy of the red allele, the animal will be black.
EBV (Estimated breeding value)
EBVs are an estimate of an animal's true breeding value based on performance data and pedigree information. An EPD is equal to half of an animal's EBV as half of an animal's genes are passed to the next generation.
Economic or Selection Index
Estimates the relative (not an absolute number) profit expected for the offspring of animals (reported as $/cow exposed). These are generated by assigning relative importance to economically relevant traits (ie, calving ease and calf survival, daughter longevity, weaning and yearling weights, feed efficiency, and carcass traits). Input and output prices are predicted using expected market trends and included in the overall model for offspring profitability. Economic indexes combine multiple economically important traits with predicted prices for inputs and outputs and report a single value for predicted profitability. Economic indexes have been used for decades in swine, poultry, and dairy genetic selection and have allowed these industries to make large progress in profitability. The ASA has two selection indexes, the All Purpose Index (API, designed for operations raising replacement heifers) and the Terminal Index (TI, designed for operations that will harvest all the calves).
EPDs

 (Expected progeny difference) Estimates the difference in the expected performance of the offspring of an individual for a specific trait, given in units of that trait. The difference between two EPDs from two different animals would tell you on average the expected difference between their offspring. For instance, if Bull A has a weaning weight EPD of 60 and Bull B has a weaning weight EPD of 50, on average Bull A's calves will weigh 10 pounds more at weaning than Bull B's calves.

Epistasis
The interaction between alleles of two different genes, frequently one allele suppresses the other allele.
Free
An animal without a copy of a particular allele and, therefore, will not pass on the defective allele to the next generation.
GE-EPDs (Genomically enhanced EPDs)
These are EPDs that have incorporated information from the DNA of the animal ~ typically from a SNP panel (either 50K or GGP-HD).
Gene
A specific section of DNA that typically codes for proteins or some other gene product. Each individual carries two copies of every gene, one from each parent.
Genome
The entire DNA sequence of an individual.
Genotype
The genetic makeup of an individual (as opposed to physical characteristics). With coat color, an animal's genotype would be what alleles for coat color they have (EE, Ee, or ee).
Heritability (h2)
The proportion of differences we observe between a population of individuals that can be attributed to genetics. We usually talk about Narrow-sense heritability which is specific to the differences observed that are attributed to additive genetic value. Heritability ranges from 0 to 1 with lower numbers being lowly heritable (not much of the phenotypic variation is due to genetics) and higher numbers being highly heritable (a larger portion of the phenotypic differences are due to genetics). Reproductive traits tend to be lowly heritable and growth traits tend to be highly heritable.
Heterosis
The improved or increased productivity of hybrid offspring compared to the parents, also known as hybrid vigor. Some traits exhibit more hybrid vigor than others; for instance, fertility is a trait with a large improvement in crossbred offspring over the parents while carcass traits typically have less heterosis. The improvement above the average of the parents is due to non-additive traits.
Heterozygous
Heterozygous means an individual has two different alleles of the same gene. An individual with one red allele and one black allele for coat color would be heterozygous (Ee).
Homozygous
Homozygous means an individual has two of the same alleles for a certain gene. A homozygous animal for the extension gene (coat color) could have two black alleles (EE) or two red alleles (ee).
Inbreeding
Mating two parents that are more closely related than average in the population. This practice reduces genetic variation by decreasing the proportion of heterozygous gene pairs and increasing the proportion of homozygous gene pairs. In doing so, there is an increased frequency of genetic defects caused by recessive alleles.
Incomplete Penetrance
Refers to the phenomenon when some animals with the genotype for a certain trait do not show the correlating phenotype. In other words, penetrance describes the proportion of animals for a certain genotype that display the phenotype. You would think this should always be one but sometimes it takes a second trigger (a second gene or something in the environment) to cause the phenotype to be displayed. A recent example of incomplete penetrance is Developmental Duplication where some of the individuals that are homozygous for the recessive allele (and should display duplicated body parts) have no outward sign of the condition.
Maternal EPD
An EPD that predicts the genetic potential of an animal's daughters. For instance, maternal calving ease measures the percentage of a sire's daughters that calved without assistance.
MBV (Molecular breeding value)
Estimation of an individual
No dominance
The heterozygote exhibits a phenotype that is exactly in between the homozygotes.
Non-Additive value
Non-Additive value represents genetic potential that due to dominance and epistatsis. This value is affected by heterosis as increased genetic diversity increases the frequency of heterozygous alleles. More heterozygous allele combinations leads to more dominant gene expression or
Outbreeding (Outcrossing)
Mating two parents that are not closely related resulting in increased genetic variation, heterozygosity, and heterosis.
Overdominance
The heterozygote exhibits a phenotype that is beyond the range of either of the homozygotes but is more similar to the dominant homozygotes.
Partial Dominance
One allele is not completely dominant over the other allele. With partial dominance, the heterozygote has a phenotype between the two homozygotes but more similar to the homozygote dominant animals.
Percentile ranking
Compares EPDs for specific traits among animals within a breed. Values range from 1 to 99 and the smaller the number the better. For example, a bull with a percentile ranking of 5 for calving ease means that he is in the top 5% of all the sires in that breed for calving ease.
Phenotype
The observable characteristics of an individual. The phenotype is influenced by both the individual's environment and their genotype. In coat color, animals with a genotype of EE will have a black coat phenotype. Environmental influences may alter the phenotype (nutrition, freeze branding, bleaching, etc.) but the genotype will remain the same.
Polygenic trait
A trait that is controlled by many genes. An example would be growth traits, most carcass traits, and the onset of puberty. Selection for these traits is most efficient by using a genetic evaluation like an EPD.
Qualitative (categorical) trait
A trait with categorical phenotypes like black or red coat color and horned or polled.
Quantitative trait
Trait with a continuous phenotype. For instance, weaning weight does not have a distinct category of phenotypes, but a large variation in the actual measure of weights. Typically, these traits are influenced by many genes (polygenic trait).
Recessive trait
A recessive trait means an animal needs to inherit two copies of that allele in order to display the trait (phenotype). This is only possible if both parents have at least one copy of this allele. If the animal inherits just one copy, then the dominant allele will drive the phenotype. Red coat color is a recessive trait. A calf must have two copies of the red coat allele (ee) to display a red coat. That does not mean both parents have to be red, they just had to carry at least one copy of the red coat allele. Mating two heterozygous black parents (Ee) would have a red calf (ee) approximately 25% of the time.
Simply-inherited trait
A genetic trait that is controlled by one or just a few genes. An example would be coat color or horned/polled. These tend to be easily selected for and you can use a Punnett Square to predict mating outcomes (frequency of the traits in the next generation).
SNP (Single Nucleotide Polymorphism)
Term describing single points in DNA sequence that differ between animals. The vast majority of the DNA sequence is the identical in all cattle (and people and mice for that matter). There are some locations in the DNA sequence where a single base or a nucleotide (adenine (A), guanine (G), thymine (T), or cytosine (C)) differs from one individual to another. For instance, Bull A may have a DNA sequence of A-G-T-T-C and Bull B may have a sequence of A-G-A-T-C. In this instance, the third base is not the same between these individuals and is called a SNP (pronounced "snip"). There are thousands of SNPs that tell us about an individual's genetic potential or relationship to another individual. The ASA has done 50K SNP testing (50,000 SNP markers) with GeneSeek in the past and now offers the GGP-HD profile (GeneSeek Genomic Profiler- high density) with 80,000 SNP markers. The resulting SNP information is included in the ASA genetic evaluation and provides molecular breeding values (MBVs). Knowing these MBVs can improve the accuracy of EPDs by an equivalent of several progeny records depending on the trait. This is particularly true in young animals that have lower progeny counts and, therefore, low accuracy EPDs.

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