An overview of basic genetic concepts such as genes, alleles, chromosomes, and genetic inheritance in animals.
Introduction to Animal Genetics – Study Notes
| Concept | Description | Example in Animals |
|---|---|---|
| Gene | Unit of DNA that encodes a functional product (protein or RNA). | MC1R gene influences melanin production → coat colour in horses. |
| Allele | Alternative forms of a gene at the same locus. | Black‑coat allele (B) vs. brown‑coat allele (b) in cattle. |
| Genotype | The complete set of alleles an individual carries. | BB, Bb, or bb for the coat‑colour locus. |
| Phenotype | Observable traits resulting from genotype + environment. | A black‑coated bull (phenotype) may be BB or Bb. |
| Dominance | Interaction where one allele masks the effect of another. | In many mammals, the dominant allele for black coat masks the recessive brown allele. |
| Homozygous | Two identical alleles at a locus (AA or aa). | A homozygous recessive mouse (hh) shows the recessive coat colour. |
| Heterozygous | Two different alleles at a locus (Aa). | A heterozygous dog (Aa) may display the dominant trait. |
| Locus (plural: loci) | Specific position of a gene on a chromosome. | The FGF5 locus controls hair length in cats. |
| Mutation | Permanent change in DNA sequence. | A point mutation in the myostatin gene leads to “double‑muscle” cattle. |
| Polymorphism | Presence of two or more alleles at a locus in a population. | Multiple alleles of the MHC genes affect disease resistance. |
| Pattern | Key Features | Typical Animal Example |
|---|---|---|
| Mendelian (simple) inheritance | Single gene, clear dominant/recessive alleles, 3:1 ratio in F₂. | Coat colour in Labrador retrievers (black vs. brown). |
| Incomplete dominance | Heterozygote shows intermediate phenotype. | Roan coat pattern in cattle. |
| Codominance | Both alleles expressed equally. | Blood type in cattle (AB). |
| Sex‑linked inheritance | Genes located on sex chromosomes (X or Y). | Color blindness in dogs (X‑linked). |
| Polygenic inheritance | Multiple genes contribute to one trait; often quantitative. | Body size in pigs, milk yield in dairy cows. |
| Maternal (cytoplasmic) inheritance | Genes in mitochondrial DNA passed from mother. | Certain metabolic disorders in horses. |