Monday, April 5, 2010

Reproductive Success

In mammals, males often have greater variance in reproductive success than females, as a result of sexual selection. How will this alter the effective population size of genes on the autosomes, the X chromosome, the Y chromosome, and the mitochondrial genome? What other factors may influence the genetic diversity on these different parts of the genome?


  1. Well Murad, it seems like no one really wants to answer your question. Its been about 4 days and there is still no comment. I hope that my answer will sufficiently answer your question, and if it doesn't, I hope that Mr. Erdmann gives me a point for attempting to answer your seemingly difficult question...

    You asked about the effect of the variance in male reproductive success and how this would affect the autosomes, sex chromosomes, and mitochondrial genome. Autosomes are all of the chromosomes other than the sex chromosomes (X and Y). Humans have 44 autosomes, 22 from each parent. The number of autosomes very however in other species. Because different males have different reproductive successes, only the genes of the successful males would be passed to the offspring during reproduction. The autosomes would mirror those of successful males. This is basic natural selection. The fittest males pass on the traits that make them fit.

    Then, you asked about the sex chromosomes. First, the genes on the sex chromosomes will mirror those of the male that reproduced with the female. Again, basic natural selection described above. But I think you are wondering about what chromosomes will be passed on, X or Y. From the mother, you always receive the X chromosome, but from the father you can receive an X or a Y. Essentially, the father determines the sex of the offspring. However, the father has no control over this. It is a 50-50 chance that the offspring receives an X or a Y. The sexual success of the male has no effect on the sex of the offspring.

    Finally, you asked about mitochondrial genome of the offspring. Im sorry to say, but this is only determined by the female because the offspring receive all of their original mitochondrial from the mother. The success of the male has no effect on the mitochondrial genome of the offspring because that is determined solely by the mother.

    There is my attempt at answering your question. I hope it is worthy of a point.

  2. The male adds the sex of the offspring, and is the one that ejaculates the sperm into the female, fertilizing the egg cell for reproduction. However, the female also plays a role in reproduction, determining the father of the child by selecting its mate species that don't require a battle for the female but a dance or possibly a pheromone. The male with the best dance or signal, representing a healthy male, will be chosen by the female to reproduce with. The male that is ultimately selected will have its genome passed down into the offspring, and as this process continues, the original fit genetics will circulate among the species until only the fittest survive and reproduce.

    For instance, let's say two bulls are fighting over a cow. The bull that wins will have its sperm into the cow, fertilizing the egg, and having its genome in the child offspring. However, despite the fitness portion of the DNA, the male does not determine anything else. The probability of a male or female offspring is, like stated above, a fifty-fifty chance due to the mother always contributing an X chromosome and the father contributing an X or Y. If repeated an infinite number of times, the expected value would be half males and half females.

    Some reproduction inefficiencies come specifically from the male gametes. The Y chromosome is subject to high levels mutation due to multiple divisions during gametogenesis of the sperm and the highly oxidative environment the sperm are stored in. Furthermore, in the Y chromosome, maladaptive genes often associate with beneficial ones, transporting both at the same time and rendering that gene nonfunctional. Another negative effect of Y chromosome is that the fact that it may never be passed down. A superb chromosome, free of mutations, could end up never handed down if the male has only female offspring; this would cause a possible loss of an advantageous genome. The Y chromosome also seems to be continually degenerating, losing approximately 4.6 genes per million years. Approximations are made that in the next 10 million years, the Y chromosome will be completely degenerated.

    These additions are all given by the male. Although the fittest male does decide in reproduction, the offspring possibilities still remain largely to chance.