And this depends almost entirely on the environment

This preview shows page 4 - 5 out of 7 pages.

advantageous. And this depends almost entirely on the environment they face 2. Natural selection only acts on the variation that already exists in a species. A common misconception about evolution is that it is moving in a specific, purposeful evolution 3. Natural selection can only act on genetic variability 4. Natural selection can only play a role in the selection of traits that affect the reproductive success of an individual Sources of Genetic Variability and The Evolutionary Process A current definition of evolution: A change in allele frequency in a population from one generation to the next Two components to the evolutionary process 1. Internal sources of variability in allele frequencies: the creation of genetic variability in individual’s upon which the evolutionary process can act 2. External factors that act upon the variability in allele frequencies: the process of evolution 1. Internal Sources of genetic variability upon which evolution can act: Changes in frequencies of individual alleles Changes in combinations of different alleles Formation of new alleles 2 major sources for changes in frequencies, combinations and new alleles
Image of page 4

Subscribe to view the full document.

1.1 Recombination : the rearrangement of genes on homologous chromosomes that occurs during crossing over in meiosis. Source of variation arising out of sexual variation; important for increasing rates of natural selection. Does not result in new alleles only changes a) Random assortment of chromosomes: during meiosis these pairs line up in different random combinations in every sex cell every time they divide. The line of chromosome pairs separate into 2 daughter cells. Each daughter cell will get either fathers or mothers version of each chromosome. For humans with their 23 sets of chromosomes: the number of different possible combinations for each gamete (male or female) is over 8,000,000, the number of different individuals that could possibly result from one human mating is about 70,000,000,000,000. Major source of variability b) Crossing over: occurs during tetrad stage of Meiosis 1 when double strands come together to form tetrads. Exchange of genetic material between homologous chromosomes during the first prophase of meiosis Sections that used to be on mothers chromosomes on fathers and vice versa. Can give new combination of alleles 1.2 Random Mutations There is already significant variability for natural selection to act on- random mutations are not necessary for evolution to progress in most species, usually already enough variability for evolution. But random mutation can result in new alleles, which can be necessary for new species Sickle Cell Anemia: random mutation that inhibits red blood cells from carrying oxygen 2. External factors that act upon variability in allele frequencies: the evolutionary process a. Non-random Mating brought about by: Sexual selection is a type of non-random mating that acts upon one sex or the other in a species. It occurs during competition for mates when specific traits are actively selected for when choosing partners. Differential reproductive success within one sex of any species. Struggle for males to gain access to
Image of page 5
You've reached the end of this preview.
  • Spring '12
  • Sandgathe
  • DNA, Cell Biology and Genetics

{[ 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