Introducing Genetics & Inheritance in Animal Care

Bio Module 7

DNA

Deoxyribonucleic Acid - nature’s instruction manual. The hereditary material that contains genetic instructions for builidng and maintaining living organisms. Found in every cell.

Genes

Specific segments of DNA that contain the instructions for building proteins for a trait (ex: the gene for coat color)

Alleles

Different versions of the same gene (ex: the gene for coat color has alleles for black, brown, etc.). Each animal inherits one allele from each parent for each trait.

Traits

The observable characteristics that result from an animals genetic makeup. Physical features and internal features that affect health (ex: ear shape vs blood clotting ability)

Dog chromosome numbers

78 chromosomes, 39 pairs

Cat chromosome numbers

38 chromosomes, 19 pairs

Horse chromosome numbers

64 chromsomes, 32 pairs

Cattle and goat chromosome number

60 chromosomes, 30 pairs

Pig chromosome number

39 chromosomes, 19 pairs

Chicken chromosome number

78 chromosomes, 39 pairs

XY sex chromosomes

Typically male sex chromosomes

XX sex chromosomes

Typically female sex chromosomes

Gregor Mendel

An Austrian monk who constructed careful experiments on pea plants in the 1860’s. Now known as the father of modern genetics.

True-breeding

A breeding line that consistently produces offspring with the same characteristics generation after generation

Hybridization

The crossing of two genetically different organisms to breed a third organism called a hybrid with a distinct, predictable set of traits obtained from it’s parents

Key points of Mendel’s work

• True-breeding lines helped establish predictable inheritance patterns

• Cross-breeding showed that some traits are dominant and some are recessive. These traits do not blend - they remain distinct.

• 3:1 ratio in F2 generations shows inheritance shows predictable mathematical patterns

• Laid foundation for calculating genetic risk in breeding programs

Recessive traits

Appear only when two recessive alleles are inherited - shows why some genetic conditions skip generations

Dominant traits

Appear when at least one dominant allele is present

Phenotype

What you can see - observable characteristics (eye color, ear shape, behavioral traits)

Genotype

The genetic blueprint - actual genetic makeup or the combination of genes an animal carries. They may have a black coat phenotype, but carry genes for both black and brown coats

Homozygous

Matching gene pairs, when an animal inherits two identical copies of a gene - two dominant (BB) or two recessive (bb). Consistently pass the same gene along to offspring

Heterozygous

Mixed gene pairs, animals with two different variations of a gene (Bb). They display the dominant trait but can pass the recessive gene to offspring.

Homozygous dominant

AA. Will always show and pass dominant trait.

Homozygous recessive

aa. Will always show and pass recessive gene.

P generation (Mendel)

The parent generation - have known genetic characteristics and establish a baseline for predicting traits in future generations.

F1 Generation (Mendel)

First generation. In the classic Mendelian experiment, one parent is usually purebred for dominant and one for recessive. Thus, all F1 offspring will be heterozygous, show dominant trait but carry recessive

F2 generation (Mendel)

Second generation - when F1 offspring reproduce with one another, the recessive phenotype begins to appear. 3:1 ratio - 3 dominant phenotypes to 1 recessive.

Law of segregation

An individual has 2 copies of the same gene. They pass one copy to each offspring.

Law of dominance

Dominant alleles are always expressed. Recessive are only expressed if no dominant allele is present.

Law of independent assortment

Different traits are inherited separately from each other → coat color inheritance doesn’t effect ear shape inheritance. Countless trait combinations.

Incomplete dominance

Neither allele is completely dominant over the other. Heterozygous animals show a blended or intermediate phenotype rather than one trait masking the other. Why some traits don’t follow simple dominant-recessive rules. Ex: blue or lilac coats.

Codominance

Both alleles are expressed equally in heterozygous individuals. Instead of blending, both traits are visible in the phenotype. Especially important in blood type and immune system genetics.

Polygenic inheritance

Two or more genes collectively influence a single phenotypic trait - continuous range of variation.

Karyotyping

An organized picture of all chromosomes in a cell, arranged by size and shape. This test can ID chromosomal abnormalities.