Looks can tell in beef cattle

Why some apples fall farther from the tree

“Boy, if he isn’t a spitting image of his grandpa!”

You’ve likely heard similar references before and they make this concept easy to grasp: Just like people,cattle don’t inherit genes equally.“

Because of random assortment and recombination, or crossover events during the sperm or egg cell formation, they can get an unequal proportion of genetic material from their grandparents,” says Bob Weaber, Kansas State University animal scientists.

Thus, an animal might favor its maternal grandfather and look nothing like the paternal one—which matters in cattle herds where sires vary greatly for economically important traits.

That’s just Mother Nature’s mechanism for maintaining genetic diversity in the population. “But from a geneticist’s perspective,” Weaber says, “we’re trying to figure out: Did they get a good assortment of genes or a bad assortment of genes from their parents?”

The question is especially relevant in explaining variation in composite cattle breeds and herds. More than a decade ago, Colorado State University professor Daryl Tatum noticed that variability when looking over the King Ranch’s Santa Gertrud is bulls.

“They all were the same percentage of Brahman and Shorthorn breeding, but there was everything from what looked like straight Shorthorn to ones that looked like a big, old red-colored Brahman,” he says. “If the genes segregated so differently in these populations to where they looked so much different, does it mean their meat quality was different as well?”

“Where it becomes more complicated is when you breed a hybrid to a hybrid,” he says. “Even though the F2s have half of their genetic material from each breed on average, some re-pairing of chromosomes from the same breed occurs.”

That explains why the heterosis advantage is diminished the second time around, though some will have more and others less than average. Using DNA to identify which ones were truly half-bloods with each chromosome in the pair coming from different breeds would help.

“You could do some pretty interesting things if you had those genotypes,” Weaber says. “You could optimize heterosis through different breeding structures.

”Of course, making sure the genes from both sides of the pedigree are superior is an insurance policy.

“You don’t dig yourself out of the hole just by crossbreeding,” he says. “The merits of the parents going into those systems are important,” especially for traits with moderate to high heritability where heterosis is low. “If you’ve got two parents that you put together, one excels and one does not, the rules of additive genetics suggest you’re likely going to produce an animal that’s somewhere near the middle.”

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