A zygote is a fertilised egg cell that results from the union of a female gamete (egg, or ovum) with a male gamete (sperm). In the embryonic development, the zygote stage is brief and is followed by cleavage, when the single cell becomes subdivided into smaller cells.
Human and most mammal male cells have one X, and a Y chromosome. Birds also have sex chromosomes, but they act in completely the opposite way. Male birds have X and Y chromosomes, and females have a single Y chromosome.
Split or / is the term used to indicate that a bird is carrying a variety or colour in a genetically hidden format that requires it in a double dose to make it visible. The exception would be sex-linked splits which is only possible with cock birds.
German speaking Gregor Johann Mendel (1822-1884) was a meteorologist, mathematician, biologist, Augustinian friar and Abbot of St. Thomas’ Abbey in Brno, Margraviate of Moravia.
Through his work on pea plants, he discovered the fundamental laws of inheritance, deducting that genes come in pairs and are inherited as distinct units, one from each parent. Mendel tracked the segregation of parental genes and their appearance in the offspring as dominant or recessive traits. He recognized the mathematical patterns of inheritance from one generation to the next. Mendel’s Laws of Heredity are usually stated as:
- The Law of Segregation: Each inherited trait is defined by a gene pair. Parental genes are randomly separated to the sex cells so that sex cells contain only one gene of the pair. Offspring therefore inherit one genetic allele from each parent when sex cells unite in fertilization.
- The Law of Independent Assortment: Genes for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another.
- The Law of Dominance: An organism with alternate forms of a gene will express the form that is dominant.
The genetic experiments Mendel did with pea plants took him eight years (1856-1863) and he published his results in 1865. During this time, Mendel grew over 10,000 pea plants, keeping track of progeny number and type. Mendel’s work and his Laws of Inheritance were not appreciated in his time. It wasn’t until 1900, after the rediscovery of his Laws, that his experimental results were understood.
Genetic linkage is the tendency of DNA sequences that are close together on a chromosome to be inherited together during the reproductive dividing of cells. Two genetic markers that are physically near to each other are unlikely to be separated and are said to be more linked than markers that are far apart.
Genes carry the information that determines traits, which are features or characteristics that are passed on to the offspring.
The resultant young in terms of colour and variety can be calculated. These are known as breeding expectations.
DNA is the abbreviation of deoxyribonucleic acid, an organic chemical of complex molecular structure that is found in all cells including many viruses. DNA codes genetic information for the transmission of inherited traits.
The chemical DNA was first discovered in 1869, but its role in genetic inheritance was not demonstrated until 1943.
Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA). Passed from parents to offspring, DNA contains the specific instructions that make each type of living creature unique.
Autosomal means that the gene in question is located on one of the numbered, or non-sex, chromosomes. The sex chromosomes are referred to as X and Y.