Adaptation
- 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:
- migrate out of the area (permanently or seasonally)
- go extinct
- 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 individual’s ability to adapt itself is an inherited trait
- to understand species adaptation, it helps to have a little knowledge about genetics
- part of an individual’s 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
- 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
SKIP THIS STUFF:
- 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
- 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)
- 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:
Evolution
See the emergence of life timeline on page 128-129
- 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
- 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
- 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
- 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
- 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