Multifactorial Traits


With one gene controlling Human hair color:
genotype phenotype
BB 1. dark brown
Bb 2. light brown
bb 3. blond

With 2 genes controlling Human hair color:
genotype phenotype
BBBB 1. dark brown
BBBb 2. brown
BBbb 3. light brown
Bbbb 4. honey blond
bbbb 5. blond

With 3 genes controlling Human hair color:
genotype phenotype
BBBBBB 1. dark brown
BBBBBb 2. brown
BBBBbb 3. light brown
BBBbbb 4. mousey brown
BBbbbb 5. dishwater blond
Bbbbbb 6. honey blond
bbbbbb 7. blond

the pattern in these data are:
(number of phenotypes) = 2 * (number of genes) + 1
genes phenotypes
1 2*1+1= 3
2 2*2+1= 5
3 2*3+1= 7
4 2*4+1= 9
5 2*5+1= 11
6 2*6+1= 13
10 2*10+1= 21
15 2*15+1= 31
20 2*20+1= 41
23 2*23+1= 47


Why would any species want to have more than one gene for any trait?

  • plants spontaneously undergo autopolyploidy,
    . . . a mechanism for creating more than one gene per trait,
    . . . with one gene for the trait per chromosome.
  • range of environmental conditions tolerated
    . . . can be broken into 2n+1 sub-ranges,
    . . . where n = number of genes or chromosomes.



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    © 2004 Prof. LaFrance, Ancilla College