Gene Basic unit of inheritance Carried on the chromosomes in the gametes Eggs from females Sperm from males Provide how animal will look Alleles Different forms of the same gene Same location on the chromosome Chromosomes Varies species to species Horses have 32 pairs, 64 individual Basic Genetics

DNA Deoxyribonucleic acid What genes are made of Genes act by causing the production of certain enzymes Control all chemical reactions in the body Must occur in pairs Chromosomes in the nucleus of a particular cell contain the same genetic info as the chromosomes in every cell of the body Example: Tongue chromosomes are the same as shoulder chromosomes However, genes know their functions and know when to “turn on and off” Basic Genetics

Genome Complete set of instructions for making an organism Contains “master blueprint” Genes consist of tight coiled threads of DNA and associated with protein molecules Genes are arranged linearly along the chromosomes Nucleus contains 2 sets of chromosomes One set from each parent Each set has 31 single chromosomes (or autosomes) And an X and Y sex chromosome Female XX Male XY Gene Descriptions

Made up of sugar and phosphate molecules Rungs of the “ladder” are nitrogen-containing chemicals called bases Each strand is a linear arrangement of repeating similar units called nucleotides Composed of one sugar, one phosphate, and one nitrogen 4 different bases are present Adenine (A) Thymine (T) Cytosine (C) Guanine (G) The particular order is called the DNA sequence Specifies exact instructions for a particular organism Structure of DNA

Each time a cell divides into 2 daughter cells a full genome is duplicated inside the nucleus Bases A – T C – G Each daughter cell receives one old and one new DNA strand How the Code Works

After fertilization (egg and sperm unite) a newborn foal will have a chromosome from stallion and from mare Now in pairs again Offspring will be genetically different because the combination occurs randomly Fundamentals of Inheritance

Random Segregation Random transfer of chromosomes and their genes to form gametes Causes major causes of genetic differences among related individuals Genetic Variation Differences in genetic makeup Randomness

Controlled by a single or few gene pairs Phenotypes Characteristics we can see Genotype Identifying genes 3 Types of Gene Action: Dominance 2 different (heterozygous) alleles (genes) for the trait are present, the dominant phenotype will be expressed The phenotype of recessive alleles in only expressed in the homozygous (same) condition Codominance 2 alleles share same phenotypic expression Blend of both parents (ex. Black and white produce spots) Partial of incomplete dominance 2 alleles influence phenotypic expression (ex. Red and white produce pink) Qualitative

Controlled by hundreds or thousands of gene pairs located on different chromosomes Economically important traits Quantitative Traits Influence of Genetics and Environment on Some Traits TraitVariation Due to GeneticsVariation Due to Environment Height at Withers Body Height Body Length Heartgirth Running Speed Walking Speed Movement Temperament Reproductive Traits

Phenotype = Genotype + Environmental Effects In an ideal environment a horse presumed to have an inferior genotype can exhibit a great phenotype To reduce environmental effects, all horses must be treated the same Phenotypic & Genotypic Expression

Most common coat colors in horses seem to be explained by the genetic effects of the alleles of at least 7 genes Determining the effects of these 7 genes is rather complex and relates to the dominant and recessive expression of each of the alleles of the 7 genes Coat Color

Defects in DNA can result in failure to form essential proteins of the formation of abnormal proteins Can cause death or disease Defects can be caused by abnormalities in a single gene, the collective effect of a group of genes, or some chromosomal abnormality Genetic Disease

Genetic Diseases of Horses Caused by a Single or Few Genes Genetic DiseaseDescription Failure of immune system to form; horse dies of infections; transmitted as recessive gene; mutation of a single gene Defect in the movement of sodium and potassium in and out of muscles; causing intermittent attack of muscle weakness, tremors and collapse; transmitted as autosomal dominant; involves on gene Failure to produce blood clotting factor, bleeding into joints, development of hematomas (blood clots); transmitted on X chromosome Lower jaw in shorter than upper jaw; incisor teeth improperly aligned Failure to form certain nerves in the intestinal tract; foals die of colic several days after birth Animals tend to be small and weak at birth; show disorders of the reproductive system; mares are sterile; caused by failure of the X chromosome to separate after duplication Accumulation of fluid within compartments of the brain; resulting in crushing of brain Hemolytic (destruction of red blood cells) disease of the newborn; caused by antibody in mare’s colostrum; results in anemia and sometimes death; underlying cause in compatibility in blood types Opening in the body wall at the navel (umbilical) or opening into the scrotum (inguinal) which allows the intestines to drop through