Chromosomes & Heredity by aR0YH3YN

VIEWS: 5 PAGES: 7

									Chromosomes & Heredity
   Chromosome Theory of Heredity
       Genes are located on the Chromosomes
       Each gene occupies a specific place
       A gene may exist in several forms or alleles
       Each chromosome has just one allele for each of its genes
SUMMARY OF SUTTON’S
WORK
   1. A pair of factors determines each characteristic in an
    organism.
   2. A gamete contains one factor from each pair.
   3. Factors assort independently during meiosis.
   4. Factors pair during fertilization to restore the original
    number of factors.
   5. Individual factors remain unchanged from one generation to
    the next.
              GENE LINKAGE
   Linked genes do not undergo independent assortment
   Effects of Gene Linkage
        Morgan’s GgWw X ggww didn’t produce expected results
        See fig. 10-4: Gene for body color & wing size are linked
      Linkage Groups
         Packages of genes that tend to be inherited together
         These “packages” are homologous chromosomes
   CROSSING OVER
      Recombinants: Individuals with new combinations of genes
   GENE MAPPING
      Sturtevant reasoned the frequency of crossing over occurs
    in proportion to the distance of the genes on the chromosome
CROSSING OVER
   During Prophase One
   Synapsis: Process of drawing the homologous chromosomes
    together by putting all four chromatids into parallel alignment.
   Nonsister chromatids break at one or more sites and exchange
    corresponding segments; and exchange of alleles.
   When alleles are different, crossing-over may occur and cause
    unlike alleles to be exchanged, which breaks up old
    combinations of alleles creating a new combination of alleles.
SEX LINKAGE
     
              SEX LINKAGE
   Sex Chromosomes
      autosomes: Same chromosomes for Males & Females
      XX = Female     XY = Male
   Sex Determination: 50% chance of male or female
   Genes on Sex Chromosomes

Genes on Sex Chromosomes
   Sex-linked: A gene located on one of the sex chromosomes
   See fig. 10-10
   See fig. 10-11

								
To top