Anthropology 101 Chapter 4

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Anthropology 101 Chapter 4
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Chapter 4
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  1. His work illustrates the basic rules of inheritance.
    Gregor Mendel
  2. Hybrids
    Offs pringof parents that differ from each other with regard to certain traits or certain aspects of genetic makeup; heterozygotes.
  3. Principle of Segregation
    Discrete units, or genes, occur in pairs because chromosomes occur in pairs.

    • During gamete production, members of each gene pair separate so each gamete contains
    • one member of a pair.

    During fertilization, the full number of chromosomes is restored and members of a gene or allele pairs are reunited.
  4. Dominance
    Dominant traits are governed by an allele that can be expressed in the presence of another, different allele.

    Dominant alleles prevent the expression of recessive alleles in heterozygotes.
  5. Recessiveness
    Recessive traits are not expressed in heterozygotes.

    For a recessive allele to be expressed, there must be two copies of the allele.
  6. Alleles
    Alternate forms of a gene.

    Alleles occur at the same locus on a pair of chromosomes and influence the same trait.

    However, because they are slightly different, their action may result in different expressions of that trait.

    The term is sometimes used synonymously with gene.
  7. Locus
    The position on a chromosome where a given gene occurs.

    The term is sometimes used interchangeably with gene, but this usage is technically incorrect.
  8. Homozygous
    Having the same allele at the same locus on both members of a pair of chromosomes.
  9. Heterozygous
    Having different alleles at the same locus on members of a pair of chromosomes.
  10. Genotype
    The genetic makeup of an individual.

    Genotype can refer to an organism’s entire genetic makeup or to the alleles at a particular locus.
  11. Phenotypes
    The observable or detectable physical characteristics of an organism; the detectable expressions of genotypes, frequently influenced by environment.
  12. Principle of Independent Assortment
    The distribution of one pair of alleles into gametes does not influence the distribution of another pair.

    The genes controlling different traits are inherited independently of one another.
  13. Random Assortment
    • The chance distribution of chromosomes to daughter cells during meiosis; along with
    • recombination, a source of genetic variation (but not new alleles) from meiosis.
  14. Mendelian Traits
    Characteristics that are influenced by alleles at only one genetic locus.

    Examples include many blood types, such as ABO.

    Many genetic disorders, including sickle- cell anemia and Tay-Sachs disease, are also Mendelian traits.
  15. Mendelian Inheritance in Humans
    • Over 19,000 human trains are known to be inherited according to Mendelian principles (Online Mendelian Inheritance in Man
    • www.ncbi.nlm.nih.gov/omim/)

    • ¨The human
    • ABO blood system is an example of a simple Mendelian inheritance.

    • ¤The A and B alleles
    • are dominant to the O allele.

    Neither the A or B allele are dominant to one another; they are codominant and both traits are expressed.
  16. Codominance
    The expression of two alleles in heterozygotes.

    In this situation, neither allele is dominant or recessive; thus, both influence the phenotype.
  17. What Dominance Doesn’t Mean
    Complete determinant of phenotype

    Better or stronger
  18. Polygenic Inheritance
    • Polygenic traits, or continuous traits, are
    • governed by alleles at two or more loci, and each locus has some influence on the phenotype.

    Hair, eye and skin color are polygenic traits
  19. Skin Color
    Coloration is determined by pigment produced by specialized cells called melanocytes

    The amount of melanin produced determines how dark or light skin will be

    Melanin production is influenced by interactions between several different loci that, until recently had not been identified
  20. Polygenic traits and racial classification
    Polygenic traits account for most of the readily observable phenotypic variation seen in humans

    Traditionally serve as a basis for racial classification

    • ¨Actually,
    • stature, shape of face, fingerprint patterns are polygenic traits

    Most can be measured, i.e. height in feet and inches or meters and centimeters
  21. Mendelian vs. Polygenic Traits
    • How can the same process of genetic inheritance produce these different phenotypic
    • conditions?

    How does the environment shape the expression of mendelian and polygenic traits?
  22. Mitochondrial Inheritance
    • All cells contain mitochondria that convert energy into a form that can be used by the
    • cell.

    Each mitochondrion contains copies of a ring-shaped DNA molecule, or chromosome.

    Animals of both sexes inherit their mtDNA, and all mitochondrial traits, from their mothers.

    • All the variation in mtDNA is caused by mutation, which makes it very useful for
    • studying genetic change over time.
  23. The Modern Synthesis
    Evolution, as it has been considered from the middle of the twentieth century, is a two-stage process:

    The production and redistribution of variation (inherited differences among organisms).

    Natural selection acting on this variation, whereby inherited differences, or variation, among individuals differentially affect their ability to successfully reproduce.
  24. A Current Definition Of Evolution
    From a modern genetic perspective, we define evolution as a change in allele frequency from one generation to the next.

    • ¨Allele frequencies are indicators of the genetic makeup
    • of a population, the members of which share a common gene pool.

    In a population, allele frequencies refer to the percentage of all the alleles at  locus accounted for by one specific allele.
  25. Microevolution
    Small genetic changes that occur within a species.

    A human example is the variation seen in the different ABO blood types.
  26. Macroevolution
    Large-scale changes that occur in populations after many generations, such as the appearance of a new species (speciation).
  27. Factors that Produce and Redistribute Variation
    ¨Mutation

    Gene Flow

    Genetic Drift and Founder Effect

    Recombination
  28. Mutation
    Mutation is a molecular alteration in genetic material:

    For a mutation to have evolutionary significance it must occur in a gamete.

    Mutation rates for any given trait are usually low

    When combined with natural selection, evolutionary changes can occur and can occur more rapidly.

    Only way to produce new genes
  29. Gene Flow
    The exchange of genes between populations.

    If individuals move temporarily and mate in the new population (leaving a genetic contribution), they don’t necessarily stay there.

    • ¨Consistent
    • feature of human evolution

    • Example: The offspring of U.S. soldiers and Vietnamese women represent gene flow, even
    • though the fathers returned to their native population.
  30. Macroevolution
    Large-scale changes that occur in populations after many generations, such as the appearance of a new species (speciation).
  31. Factors that Produce and Redistribute Variation
    Mutation

    Gene Flow

    Genetic Drift and Founder Effect

    Recombination
  32. Mutation
    • ¨Mutation
    • is a molecular alteration in genetic material:

    • ¤For a mutation to
    • have evolutionary significance it must occur in a gamete.

    • ¤Mutation rates for
    • any given trait are usually low

    When combined with natural selection, evolutionary changes can occur and can occur more rapidly.

    Only way to produce new genes
  33. Genetic Drift
    Genetic drift occurs solely because the population is small:

    • Alleles with low frequencies may not be passed to offspring and eventually disappear from the
    • population.
  34. Recombination
    • Recombination doesn’t change
    • allele frequencies, or cause evolution.

    Recombination changes the composition of parts of chromosomes

    • Recombination affects how some genes act, and slight changes of gene function can become
    • material for natural selection to act upon.
  35. Natural Selection
    Natural selection provides directional change in allele frequency relative to specific environmental factors.

    • ¨If the
    • environment changes, selection pressures also change.

    If there are long-term environmental changes in a consistent direction, then allele frequencies should also shift gradually each generation.
  36. Sickle-cell Anemia
    • A severe inherited hemoglobin disorder in which red blood cells collapse when deprived
    • of oxygen

    It results from inheriting two copies of a mutant allele.

    This mutation is caused by a single base substitution in the DNA.
  37. Why It Matters
    Many human disorders are caused by  mutations in genes at one locus. The more we know about Mendelian disorders, the better prepared we are to make decisions due to a family history of genetic difficulties.
  38. Huntington Disease
    Huntington disease affects about 1 out of every 100,000 people and is caused by a dominant mutation on chromosome 4.

    A person with the allele has a 50% chance of passing it their offspring.

    There is no cure and symptoms most often occur between ages 35 and 45.

    • By this time, most people who want children have had them and may have passed the
    • mutant allele on to their offspring.
  39. Why It Matters
    Suppose one of your parents was diagnosed with Huntington disease.

    Would you be tested to determine whether you carried the allele for the disease?

    If you have the test, you will either be relieved by the results or know that you’ll develop a neurological disease that will ultimately kill you.

    • This scenario illustrates why people should be 
    • informed about how traits are inherited.

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