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Chicken Genetics 1 - Basic chicken genetic terminology - an introduction

This is an introduction to the genetics of chickens, starting with the meaning of some terms – chromosome, gene, homozygous, heterozygous, dominant, recessive or split, and the punnett square. Nature vs Nurture. Some characteristics are inherited, and others come about because of environmental factors, but really most are actually a mixture of both. You inherited your skin colour from your parents, but if you happen to be well tanned when you have babies of your own, your skin’s tan doesn’t get reflected in the colour of your baby’s skin. We see this combination of inheritance and environment in chickens too. A chicken inherits the genetic code for a certain amount of brown coating for its eggs. A hen that lays white eggs will never start laying brown eggs, because she doesn’t have the genetic background to do so. The genes for egg colour are inherited from both the hen and the rooster, and are quite predictable. DNA is a very long thin molecule with a structure like a twisted ladder. The sides or uprights of the ladder are made of phosphate and a sugar (deoxyribose), and the rungs are each a pair of nucleotides. Together the arrangement of these nucleotides make up the DNA code which is interpreted by the cell as instructions about how to grow and behave. The DNA inside the cell is organised into chromosomes, and in fact into pairs of chromosomes, because we inherit one of each pair from each of our parents. Humans have 46 chromosomes, but chickens have 78 chromosomes, that’s 39 pairs. Although the DNA code continues right along the whole length of each DNA molecule, we pay most attention to some sections of the DNA molecule that carry specific genes of interest. A gene is the basic unit of inherited information, it’s a section of DNA that codes for a particular inherited thing. The shape of a chicken’s comb can demonstrate some other genetic terms. Comb shape is inherited. A purebred leghorn rooster will pass on one gene for a single comb to his offspring, and a purebred leghorn hen will also pass on one gene for a single comb. So the purebred leghorn chicken will have two genes for single comb, and will express these by actually having a single comb on her head. When an animal has two identical genes, we use the word homozygous, which means two genes the same. A purebred leghorn with a single comb is homozygous for the single comb gene. In a similar way, a purebred Wyandotte chicken will be homozygous for the rose comb gene. If we cross our purebred Wyandotte chicken with a purebred leghorn, our new baby chicken will get one gene for comb shape from its mother and one gene for comb shape from its father so will have one rose comb gene and one single comb gene. The baby chicken’s actual comb shape will be a rose comb, because the gene for rose comb is a dominant gene. Dominant just means that the gene will be expressed even if there is only one copy of it. Although the purebred Wyandotte had two copies of the rose comb and our baby chick has only one copy, the dominant rose comb gene expresses itself and the comb on the chick’s head will a rose comb, just like Mum’s. The single comb gene is a recessive gene. It doesn’t manage to express itself in the baby’s comb shape unless it is present in homozygous form. We use the clue of the capital and lower case letters to denote this dominant or recessive quality of the gene. Our baby chick isn’t homozygous, it has one of each type of gene. In human and animal genetics we would say that the baby chick is heterozygous, but in chickens we often say that the baby chick is “split” for the single comb shape – meaning the baby has a gene for a single comb but that gene is hiding under the dominant rose comb gene expression. So that’s a basic introduction to some genetic terms. It gets more complicated, and it gets more fun as well as more useful. I’ll talk about that in another video. The music used in the introduction and end of this video is from a game called Mixed Genetics. For more fascinating facts, hints and tips about caring for your chickens, and the sheer pleasure of chickens, subscribe to my channel: Chickens in my garden - New Zealand    / chickensinmygarden   Catch up with me on Facebook   / chickensinmygarden