Breeding and Selection Part 1

Phenotype

the observable characteristics of an individual.

Genotype

the genetic constitution of an individual.

Locus/Loci

where on a chromosome a particular gene/genetic marker can be found.

Chromosome

thread-like structure made up of DNA which contain genes.

Gene

the basic unit of heredity which can pass from parent to offspring.

Gamete

reproductive cell; female = ova/egg cells, male = sperm cells (haploid cells).

Progeny

another word for offspring.

Animal Breeding

the process of selective mating of animals with desirable traits to maintain or enhance these traits in future generations.

Qualitative Traits

traits that can be classified into categories and are controlled by a single or a small number of genes.

Quantitative Traits

traits that cannot be classified into category and are controlled by a larger number of genes (polygenic) and can be affected by the environment.

Mendelian Inheritance

inheritance patterns following laws of segregation and independent assortment.

Fisher's Infinitesimal Model

variation in quantitative traits influenced by an infinitely large number of genes, each making an infinitely small contribution to the phenotype.

Breeding Programmes

function to increase production, productivity, product quality and cost efficiency.

Genetic Diversity

the variety of genetic characteristics within a species.

Animal Welfare

the well-being of animals, considering their physical and psychological needs.

Sustainable Systems

practices that maintain the health of the environment while meeting human needs.

Heritability

the proportion of observed variation in a trait that can be attributed to inherited genetic factors.

Breeding Value

an estimate of the genetic value of an individual as a parent.

Crossbreeding

the practice of breeding animals from different breeds to produce offspring with desirable traits.

Selection

the process of choosing individuals with desirable traits for breeding.

Production Efficiency

the ability to produce more output with the same or fewer inputs.

Product Quality

the characteristics of a product that meet the needs and expectations of consumers.

Single Locus/Qualitative Traits

Traits determined by a single gene, with distinct phenotypes.

Genotype RR

Phenotype RED.

Genotype rr

Phenotype WHITE.

Genotype Rr

Phenotype ROAN (white and another colour).

Examples of Single Locus Traits

Coat colour and polled vs. horned cattle.

Epistatic interactions

Action of one gene on another; one gene can mask another.

Albinism

Complete lack of melanin producing cells.

Leucism

Lack of some melanin producing cells.

Melanism

Excessive production of melanin in cells.

Complex Vertebral Malformation (CVM)

Mutation in SLC35A3 Gene.

Three Genotypes and two phenotypes in CVM

+ and + (normal), + and CVM (normal), CVM and CVM (affected).

Law of Segregation

Members of a gene pair separate into the gametes, such that half carry one member of the gene pair and half carry the other.

Law of Independent Assortment

Genes controlling separate traits segregate independently.

Polygenic/Quantitative Traits

Phenotypes are measured on a continuous scale and affected by the environment.

Breeding Value

Predicts progeny phenotype based on parental alleles.

Best Linear Unbiased Prediction (BLUP)

Method of estimating random effects.

Heritability (h2)

Proportion of the superiority in performance of the parents in a trait that is passed onto their offspring.

Pleiotrophy

Some genes influence more than one trait.

Antagonistic corrections

Negative links that can slow down genetic progress.

Negative correlation between milk yield and fat percentage

Selecting for milk yield could decline fat percentage.

Quantitative Traits; Heritability - Type/Conformation

High; 0.4-0.5.

Quantitative Traits; Heritability - Quality

Moderate; 0.2-0.35.

Quantitative Traits; Heritability - Production

Low; 0.05-0.15.