Evolution help!?

Question

Suppose that within a population of zebras, 111 out of 403 exhibit a recessive hoof trait. In the next generation, 192 out of 598 zebras exhibited the same trait. Show the steps involved in determining whether evolution has occurred

Answer 1

Evolution is simply a change in allele frequency with time. Assuming that the hoof trait is the function of a single gene, the recessive allele must be homozygous in 27.5% of the first generation, and 32.1% in the second generation. This is already good evidence for evolution, but to be sure we also need to compute (or reasonably guess) the heterozygous frequency of the allele.

There's a simple way to do that. Let R be the population frequency of the recessive allele, and D be the population frequency of the dominant allele. (R + D = 1)

Then the frequencies in the total population will break down into four groups: R^2 + RD + RD + D^2 = 1. In the first generation, we know that R^2 = .275, so R will be the square root of that, or .53 -- which means D must be .47.

In the second generation, R^2 = .32, so we take the square root to find R = .57, so D = .43. Therefore the frequency of the recessive allele has increased in the population, which means that evolution has occurred.

Answer 2

You can't really know the answer to this without knowing the overall frequency of the recessive gene. We also don't know the mating pairings, and that makes a big difference. While it seems like a drastic increase, we also know that with roughly 1/4 of the population being homozygous recessive that any mating between Zebras exhibiting the recessive trait will result in progeny that also exhibit the trait. We also know that any mating between a Zebra exhibiting the trait and a heterozygous individual not exhibiting the trait will result in a Zebra exhibiting the trait 50% of the time. I could go through all the rest of the iterations, but the point is, that without knowing the frequency of the gene (ie the number of heterozygous individuals) we can't know the expected frequencies and ratios based on a random mating model, nor a skewed mating model. Therefore without interfering with the population by either DNA tests, or breeding experiments to uncover heterozygosity, you can't really determine whether or not evolution has occurred.

Answer 3

This actually doesn't show anything. Of the 403 zebras, approximately 28 percent had the hoof trait. Of the 598, 32 percent had the hoof trait. This shows nothing. Evolution is random mutation acting on natural selection. In clearer terms, mutations (which are shown here) that help the organism are passed down from generation to generation, and the animals without that mutation eventually die off. Although the percent did increase between generations of the zebra's, it is not clear if the hoof trait actually helped the zebras. It may just be a genetic flaw. Evolution does not cover this. I hope this helps.

Answer 4

p1 = 111/403 = 0.275

p2 = 192/598 = 0.332

The frequency of the recessive trait in the population is increasing.

I would run a χ-square test on each generation to determine if the variation from the 1:3 ratio (0.250) is statisticly significant.

Answer 5

Many organisms have similar body plans. Horses', donkeys', and zebras' bodies are set up in pretty much the same way, because they are descended from a common ancestor. As organisms adapt and evolve, not everything about them changes. The differences, such as the zebra's stripes, show that each species adapted to its own environment after branching off from the common ancestor.

The bodies of deer, moose, zebras, and horses are very similar, and these animals are very closely related. One major difference is that deer and moose have antlers and zebras and horses don't. Why is this? Deer and moose live alone or in small groups, while zebras and horses live in large herds. Living in a herd provides its own protection from enemies: it is easier to attack an individual than a huge herd. Therefore, herd-living animals do not need the antlers that their loner relatives need for protection. In addition, running or grazing with large antlers is hard to do in a herd, where it is easy to accidentally stab one's neighbor.

Answer 6

I'd assume that since the trait is recessive and the ratio increases pretty drastically from one generation to the next, just a comparison of the two ratios would be needed for evidence. Hope that helps!

Answer 7

I would think getting a sample from one generation to the next immediate generation would not be a true test.
Seems you would have to closely monitor the zebras over the next 20 years to even begin to get an idea whether evolution is occurring, if any.

Answer 8

i dont know the steps but the population fo these hoof trait zebras will increase and more and more will have the recessive hoof trait

Answer 9

Evolution does not occur from one generation to the next. You need to study many generations before you can even begin to determine whether natural selection has occured or whether the variations are all within the normal range of expression.

Answer 10

It cannot be proven in your example.

Seriously.

Evolution is not the simply reassignment of genetic traits. You can't say that evolution is happening if one generation has mostly brown eyes, and the next has more blue eyes. There is a huge element of statistical probabilities here, and random chaos theory would apply as much as any sense of "evolution."

Hell, in a group of 100 chimps, none could ride a bicycle. In the next generation, 1 out of 1000 could ride a bicycle. Evolution! Yeee haaaa! and the next generation will have one walk upright? Okay, I'll tone down the obvious sarcasm, but you get my idea.

If we were talking about eons of zebras, then I might... MIGHT... be willing to talk evolution. But no way would I look at two successive generations and declare "evolution."