Of Hybrid Vigor, Sex Determination and Sex-Linked Traits

This is a continuation of a seven-part series that we started during the World Cockfighters Day.

Lesson Five:

Hybrid Vigor. The main reason for outcrossing is to establish a high degree of “Hybrid Vigor,” which is the opposite of “Inbreeding Depression.” To breed an individual that is bigger, better, faster, stronger, smarter and gamer than his parents is in fact the result of hybrid vigor. To realize the greatest benefits of hybrid vigor, you must maintain a high degree of heterozygosity by continually outcrossing or semi outcrossing. This will involve the constant search for new blood. If you are deciding to create homozygosity through inbreeding or heterozygosity through cross-breeding, consider these two points: how important is predictability to your breeding program? Do you want to hide the bird’s genetic weaknesses and hope that they will never show up, or do you want to force them to the surface so that you can cull or eliminate them?

Lesson Six:

Sex Determination and Sex-Linked Traits. A cock has 39 pairs of chromosomes – one pair of sex chromosome and thirty-eight pairs of autonomic chromosomes – while a hen only has one sex chromosome instead of a pair. A cock gives a sex chromosome to every fertilized egg while the hen only gives her sex chromosome to maybe 50 percent of the fertilized eggs she lays.

If a fertilized egg receives sex chromosome from both the cock and the hen, it will hatch to be a stag. But if the egg only has a sex chromosome from the cock, it will hatch out to be a pullet. The sex determination really depends on the hen so don’t blame the cock if you hatch out all pullets. Since the hen doesn’t give the pullets her sex chromosomes, a pullet does not receive any genetic information from the hen. The stag, meanwhile, receives all the genetic information. When a hen with a certain sex-linked trait is bred to a cock without it, the stags rather than the pullets receive it. Since all the pullets are like their fathers and the stags are like their mothers, this is called “crisscross inheritance.” This allows the sex-linked sorting of chicks according to such things as their leg color.

In order to understand breeding, you have to know a little about genes. A gene is the hereditary unit that transmits characteristics from parents to offspring. Each chick receives two genes, one from its mother and one from its father. The two genes match up into pairs of like function. If the paired genes are identical, they are called homozygous (a Greek word meaning “same pair”). The closer they’re related and the more inbred the birds are, the more homozygous they will be and the more predictable their offspring will be. When genes are paired different, they are called heterozygous (a Greek word meaning “different pair”). When heterozygous chickens are bred or out-crossed, their offspring are unpredictable. The genes of this offspring can pair off in all different directions as well as produce many combinations. So be careful when bringing in new blood, you might not like what you get.

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