Bio CH 15

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Bio CH 15
2011-04-27 23:00:17

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  1. Wild Type and mutant phenotypes
    • tracing genes to chromosomes:
    • Included identifying mutant phenotypes
    • trait also called the wild type.
    • ex: Most common trait is red eyes. Most common
    • Alternative trates called mutant phenotypes
    • Ex: Less common trait is white eyes
  2. Chromosomal Basis of Sex
    • Humans have XX (female) and XY (male)
    • -These are two varieties of sex chromosomes
    • eggs (x) sperm: (x or y)
    • 50/50 chance of offspring sex

    • Other chromosomal systems exist
    • -variable by species
  3. Sex Linkage
    • Genes are located on either sex chromosomes
    • X chromosome has non-sexual characters
    • X chromosome larger, other genes present
    • --Y chromosome is mostly sex characters
    • Fathers pass linked genes to daughters only
    • --X from father + X from mother ->XX daughter
    • --Y from father + X from mother ->XY son
    • More males with sex-linked disorders
    • --Females need recessive from both parents
    • --Males only need a recessive allele from mom
    • ---Can result in Color blindness, muscular dystrophy, hemophilia.
  4. X inactivation
    • Females inherit two X chromosomes (XX) However, one becomes inactivated. Inactive X condenses->Barr body. Barr bodies reactivate in ovarian cells. Prevent overexpression of X genes (dosage compensation)
    • Mosaic of cells with alternative active Xs--Patchiness of gene expressions. Ex: Toriseshell cats.
  5. Linked Genes
    • Usually located on same chromosome--Chromosomes passed along as a unit.
    • Expected ratio of phenotypes not found. Linked genes do not assor independently where one gene goes, so does the other.
    • Genetic recombination can still occur by crossing over can separate the linked genes.
  6. Mapping Genes
    • •Recombinant % data can create gene map
    • •Space between genes: recombination %
    • –Genes far apart: increased recombination %
    • •Greater chance of crossing over separating genes
    • –Genes closer: decreased recombination %
    • •Lesser chance of crossing over separating genes
  7. Nondisjunction
    • Homologous chromosomes do not separate
    • two of the same chromosome->one daughter cell
    • No chromosome-> other daughter cell
  8. Aneuploidy
    a result of nondisjunction. there is a wrong chromosome number in zygote.
  9. Trisomic
    fertilized egg is 2n+1
  10. Alteration of individual chromosome structure
    • Mulitiple Sets of chromosomes=polyploidy
    • ex: Triploidy 3n; Tetraploidy: 4n
    • Can result from complete nondisjunction
    • -All chromosomes to one cell, none other
    • Not uncommon in plant kingdom
    • -results in speciation
    • Rare in higher animals
  11. Genomic Imprinting
    • Some traits affected by parental source
    • --Different effect if gene from mother or father
    • --Vs. typically, alleles have equal effect
    • New imprinting with each generation
    • -Previous imprinting "overwritten" in gametes
    • Methylation (-CH3) of cytosine involved
    • -Additional functional group silences allele
    • One of many epigenic factors
  12. Extranuclear Genes
    • Exhibit non-Mendelian inheritance patterns
    • Ex-DNA in mitochondria, plastids (plants)
    • Not distributed by rules of meiosis
    • Organelles with genes passed in cytoplasm
    • -Cytoplasm comes from egg (maternal)
    • Therefor, Genes of plastids are maternal only and genes of mitochondria are maternal only.