The random shuffle of genes : putting the E in EPD
Abstract
"Even though expected progeny differences (EPDs) have been used by the beef industry for more than 40 years, many misconceptions still exist. Occasionally we will hear a producer say something like, 'I bred my cows to a low birth weight bull, but I had a couple of large calves.' What the producer does not realize is that this is to be expected based on the inheritance of complex or continuous traits. Let's look at this more closely.A calf inherits about 50 percent of its DNA from its sire, with the other 50 percent coming from its dam. Each sperm that is produced by a sire is a random sample of that sire's chromosomes and genes. Cattle have 30 pairs of chromosomes. So, when a sperm is produced, it is similar to flipping 30 coins. If we label the chromosomes the sire inherited from his father as blue/paternal and the chromosomes inherited from his mother as pink/maternal, there are 1,073,741,824 possible combinations of the sire's paternal and maternal chromosomes (Figure 1). And this number ignores the swapping of parts between paternal and maternal chromosomes in a biological process called recombination. So, the number of possible chromosome combinations is in the billions! We often state this as progeny receive a random sample of the sire's genes, and with billions of possible combinations no two sperm are exactly alike (the same is true for eggs produced by the dam)."--First page.
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