A single part malfunctions and the new versions of

Info icon This preview shows pages 21–23. Sign up to view the full content.

View Full Document Right Arrow Icon
a single part malfunctions, and the new versions of that part are somehow different from what they had been. Chances are the watches made with the “mutant” part will not keep time; after all, every part was carefully designed to fit with every other part. On rare occasions, however, the mutant part may have no effect on the functioning of your watches, or may cause them to work even better than the original. If that is the case, you would not be anxious to repair your part-making machine.Your new watches would be at least as good, perhaps even better, than your old watches. The history of life on Earth is a history of random mutations, most lost forever due to their deleterious effects, many simply carried along from generation to generation because they have no effect on the survival or reproduction of their recipients. But oc- casionally a copying error has produced an organism better suited to survive the rigors of life.The lucky recipients of beneficial mutations have gone on to produce many off- spring and left many copies of that new allele in the next generation. Mutations are the ultimate source of new alleles. If errors never occurred during gene replication, all of life on Earth would resemble the first living thing (whatever that was—a topic addressed in Chapter 9). Despite the mostly deleterious effects of mutations, evolution would be impossible without them. Mutations That Kill Genes are copied during sexual reproduction, when gametes receive one copy of each allele, but they are also copied when organisms grow, making more cells that compose the living tissue. Can mutations occur in growing, nonreproductive tissues as well as reproductive tissues? What effect would mutations in nonreproductive tissues have on evo- lution and natural selection? How do mutations relate to cancer or other human diseases? Are you likely to be carrying any mutations in your genes? Piecing It Together Variety is more than just the spice of life; it is the raw material upon which natural se- lection operates.Without it, there could be no evolution. Some of the genetic reasons for differences between individuals are summarized here: 1. The number of different phenotypes that can result from alleles coming together in new combinations as a result of sexual reproduction is essentially infinite.We can see this when we mathematically estimate the number of possible phenotypes arising from just a few traits. 2. Genetic traits can work together in combinations that enhance or hinder the survival and reproduction of their owners. In other words, having a certain trait may or may not provide an advantage, depending on the other traits that are present. Exploration
Image of page 21

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
82 C HAPTER 3 Mendelian Genetics: How Are Traits Inherited? Figure 3-13 The flowers of the four- o’clock plant. It appears that the flower color trait of the four-o’clock exhibits blending in the generation. However, when pink-flowered plants of the generation were crossed with each other, all three phenotypes illustrated here were present in the generation. Pink-flowered
Image of page 22
Image of page 23
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern