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Ecosystems--Adaptation

  1. Adaptation
    1. for any species, the match between its optimum or tolerance ranges and the range of actual values for a locale will determine whether or not that species will exist there and if so, how well it will do
        • if the existing values are unfavorable, the organisms facing the hardship have three alternatives:
            1. migrate out of the area (permanently or seasonally)
            2. go extinct
            3. adapt
        • adaptation can occur on two different scales:
          • each individual can change its own physiology to some extent to fit into its environment, a process known as acclimitization
            • these changes are limited and are not passed on to offspring
          • alternatively, a group of individuals (a population or subpopulation) can produce offspring which are better suited to some set of environmental conditions
            • this is species adaptation
            • each individual stays the same, but the preferred ranges of future generations are more suited to the actual conditions
            • each individualís ability to adapt itself is an inherited trait
    2. to understand species adaptation, it helps to have a little knowledge about genetics
        • part of an individualís make-up is determined by biochemical information passed down from the parents ("nature")
          • this is called the genotype
          • the study of this transmission of info or genotypes from one generation to the next is called genetics
        • the specific characteristics of an individual is largely determined by environmental factors ("nurture")
          • the sum of individual characteristics is called the phenotype
        • NOTE: the individual is shaped by its past and present environment; but we tend to separate out the effect of the environment before the individual's birth under the heading of genetics
    3. The chemical basis of inheritance
        • genes
          • the genotype is made up of genes, which are patterns within a molecule called DNA (deoxyribonucleic acid)
            • DNA is composed of repeating subinits; the
              • some patterns of subunits determine the pattern of amino acids in proteins
              • other patterns affect gene expression: the timing and control of protein synthesis
            • the DNA in most plant and animal cells is bound together with special proteins in units called chromosomes
              • the spot on a chromosome occupied by a given gene is called its locus (plural = loci)
          • chromosomes are usually present in sets of two called homologous pairs; the two chromosomes in each pair may not be identical, but they do contain the same genes (a specific gene codes for a specific protein or trait, but it can have several versions called alleles)
        • inheritence
          • in mitosis, the form cellular reproduction carried on by somatic cells, an exact copy of each pair goes into the progeny cell
          • in meiosis, the form of cellular reproduction used by germ cells to produce sperm or egg cells, only one member of each pair is passed on
            • some shuffling between each pair also goes on (called recombination)
          • when a sperm and egg cell join to form a zygote, the pairs are reunited; hence a zygote gets half its genetic material from each parent
        • gene pool
          • the total set of all genes in a population
          • traditional (Mendelian) genetics studies the frequency patterns of genetic traits (and by extension the frequency of the genes that control those traits)
        • mutations
          • the formation of new alleles by chemical changes within a gene
            • mutations are usually fatal; if the mutated cell survives it may be transformed and become cancerous
            • if the mutated cell is a germ cell (ie, sperm or egg producing) a non-fatal mutatuion may cause a change in organism genotype in the next generation
        • migration
          • mixing between previously separated gene pools
        • inbreeding
          • isolation of segments of the gene pool can cause a great decrease in the frequency of a particular genotype
  2. SKIP THIS STUFF:
    1. The Hardy-Weinberg law frequency of a genotype based on the frequency of its alleles:
        • freq (MM) = freq (M) * freq (M)
          freq (MN) = 2 * freq (M) * freq (N)
        • assumes:
          • infinitely large population
          • random mating within the population
          • no advantage to one genotype over another
          • no other factors that might affect genotype
    2. Dominant/Recessive genes
        • sometimes the phenotype only represents one member of the pair of two different alleles making up the genotype (a heterozygous pair)
          • in this case, the member of the pair which is expressed is called dominant, the member which is hidden is called recessive
            • for a recessive gene to be expressed it must be present as both member of the gene pair (a homozygous pair)
    3. Sex-linked characteristics
        • there is one pair of chromosomes which are not strictly homologous = the sex chromosomes
          • in females, the members of the pair (X chromosomes) are homologous
          • in males, one member of the pair is an X chromosome, the other member (the Y chromosome) is missing some loci
          • recessive characteristics with genes in the missing loci are called sex-linked because they are more common in males than in females (eg baldness)
            • ironically, males inherit these traits from their mothers

    OK, RESUME:

  3. Evolution
  4. See the emergence of life timeline on page 128-129

    1. selection
        • when a genotype gives rise to a phenotype which is more likely to reproduce, the frequency of that genotype increases by the process of natural selection
    2. adaptations
        • new traits arise at random, some of these can be selected by a changing environment
        • when a population shows a new trait that increases its success in a changing environment, it is said to have adapted to that environment
        • the new traits are called adaptations
    3. speciation
        • when a segment of a population becomes unable to interbreed with its original population, it is said to have formed a new species
        • this goes on a result of geographic or behavioral isolation of groups of individuals
        • note that mutation rarely results in a new phenotype and isolation rarely results in a new species
    4. hybrids
        • the offspring of two parents of different species is called a hybrid
        • hybrids may be able to breed with each other, with members of the parent species, or not at all
    5. extinction
        • the natural or artificial disappearance of a population or species
        • apparently rampant nowadays due to destruction of habitats by humans
          • occurring across a wide range of species

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ANTHONY G BENOIT
ROOM 201B
(860) 885-2386

abenoit@trcc.commnet.edu